Search

The main goal of this study is the modeling of ultimate tensile strength produced by friction stir welding of AA2024-T3 aluminum alloy using Taguchi and surface response methodologies. The considered process parameters are tool rotation speed, tool traverse speed, and wiper™ tool geometry (shoulder diameter). Analysis of variance, signal to noise ratio, and main effects plot used to check which process parameters were statistically significant and have better quality characteristics. Linear regression model was used to predict the ultimate tensile strength of the welded joints by incorporating process parameters. By using sensitivity analysis, the effectiveness of process parameters and the most significant parameter have been shown. From this research, the optimal experimental condition which gives the maximum ultimate tensile strength was obtained with a tool rotation speed of 750 rpm, a tool traverse speed of 100 mm/min, and a tool shoulder diameter of 12 mm which is 84% of joint efficiency of the base metal. The ultimate tensile strength increased to a maximum value and could be decreased with increasing tool rotation speed. Moreover, increasing the tool traverse speed or the tool shoulder diameter also make it decreased. Microscopic analysis showed that the increasing of the tool rotation speed or tool shoulder diameter results in an increase of average grain size in the nugget zone while it decreased slightly as tool traverse speed increases. [ABSTRACT FROM AUTHOR]

This study proposed the direct extrusion and continuous-shear deformation (DECS) process for the co-extrusion of Mg-AZ31B/Al 6063, aiming to prepare high-plasticity Mg/Al composite sheets. The effect of extrusion temperature on the microstructure and mechanical properties of the Mg/Al composite sheet was systematically studied. The results show that Mg/Al composite sheets with no voids or cracks at the interface were successfully prepared by the DECS process. The microstructure of the Mg layer at different extrusion temperatures primarily consists of equiaxed fine grains, with grain sizes of 7.29 μm, 8.98 μm, and 9.88 μm at 330℃, 360℃, and 390℃, respectively. The Mg layer exhibits a typical extrusion texture, with the c-axis of most grains parallel to the transverse direction (TD). With the increase in extrusion temperature, the c-axis of some grains deviates from the TD toward the normal direction (ND). The Al layer mainly consists of elongated deformed grains and fine dynamically recrystallized (DRXed) grains distributed along the extrusion direction (ED). The AZ31 Mg alloy with refined grains maintains the ultimate tensile strength of the Mg/Al composite sheet, while the Al matrix enhances its plasticity. At 330℃, the Mg/Al composite sheet shows an ultimate tensile strength of 244.48 MPa ± 4.35 and an elongation of 39.42% ± 0.06. The influence of the bonding layer thickness on the shear and tensile properties of the composite sheet was studied, revealing that increasing the bonding layer thickness reduces the shear strength of the Mg/Al composite sheet but positively affects its tensile strength. [ABSTRACT FROM AUTHOR]

Additive friction stir deposition (AFSD) is attractive for its ability to create freeform and fully dense structures without melting and solidification. Hence, additive friction stir deposition is an alternative to fusion-based additive manufacturing technology. In this study, the influence of the AFSD parameter (i.e., rotational speed and feed rate) on the mechanical properties and microstructure of 6061 aluminum alloy is investigated. The as-deposited 6061 aluminum alloy exhibits a relatively homogeneous microstructure with extensive equiaxed grains. Compared to the feedstock material, the ultimate tensile strength of the as-deposited 6061 aluminum alloy decreased to 65% from 320 to 210 MPa. The results of electron backscatter diffraction indicate that continuous dynamic recrystallization occurs during the AFSD process. Furthermore, it is evidence that the grain size and ultimate tensile strength are positively correlated with feed rate and rotational speed, whereas the elongation at break decreases with the increase in feed rate and rotational speed. [ABSTRACT FROM AUTHOR]

In friction stir welding, geometrical and motion features of the tool or pin greatly influence the interaction between the tool and workpiece as well as the resulting joint microstructure and mechanical properties. In order to enhance the material flow by optimizing the tool geometrical features, a new strategy was proposed in this study to introduce eccentric motion by offsetting the pin from the tool shoulder, and thin Al–Mg-Si aluminum alloy plates were friction stir welded by varying the pin eccentricity. The material flow and mixing characteristic were analyzed by optical microscope and tracer material method. The grain size and micro-texture of the stir zone were analyzed by electron backscatter diffraction. Uniaxial tensile tests and digital image correlation were conducted to evaluate the mechanical properties and observe the in situ strain evolution. The results show that pin eccentricity has a positive effect on promoting the material flow and grain refinement in the stir zone. The texture intensity was increased as pin eccentricity was introduced, and the dominant texture component converted from C {001} < 110 > (without eccentricity) to B / B ¯ {112} < 110 > when eccentric pin was used. However, no discerning change can be seen in the thermal history between samples. Despite the variation in softening of the stir zone with eccentricity, the ultimate tensile strength change was negligible. The average ultimate tensile strength reached approximately 198 MPa regardless of the pin eccentricity, and all joints fractured at the heat-affected zone. However, the softened stir zone caused by pin eccentricity resulted in an obvious increase in the joint elongation. It can be concluded that pin eccentricity significantly improved the material flow and grain refinement in the stir zone as well as enhanced the toughness of the weld joint. [ABSTRACT FROM AUTHOR]

Lightweight bent aluminum profiles are widely utilized in transportation fields. In this paper, the torsional channel self-bending extrusion process (TCSE) was adopted to machine AA6063 bent aluminum profiles in a single operation to verify the process's feasibility. Effects of extrusion parameters on the curvature, microstructure, and mechanical properties of the profiles were researched, and the extrusion process was simulated. The results show that the extruded profiles had good curvature stability. The grains were equiaxed in the cross longitudinal section, and the grain size at the outside diameter (OD) position was smaller than the inside diameter (ID) position. When the difference in deformation temperature at the OD edge was above 31 K, a smaller peripheral coarse grain (PCG) layer was formed at the OD edge with a thickness of about 400 μm, resulting in reduced hardness. The Mg2Si particles served as the main strengthening phase, which increased in number and decreased in size with increasing billet temperature and extrusion speed. Increasing the billet temperature and speed improved the mechanical properties of the material, with an increase in average hardness of 55.9% and 19.5%, and ultimate tensile strength (UTS) of 12.5% and 7.1%, respectively. By comprehensively considering the factors of extrusion load, microstructure, and mechanical properties, the optimum bent profile for different curvatures was determined. When a large curvature (≥328.67 mm) was required, it was preferred to increase the billet temperature. When a smaller curvature (≤328.67 mm) was required, it was advisable to increase extrusion speed. [ABSTRACT FROM AUTHOR]

This manuscript describes the study of density, porosity, microstructure, formation of phases, elemental distribution, tensile properties, fractography, microhardness, fracture toughness, and abrasion resistance of multi-layer deposition Ti-6Al-4V-5Ni alloy developed by μ-plasma metal additive manufacturing (μ-PBMAM) process for high temperature and high strength applications. It also presents comparison of these aspects with multi-layer depositions of Ti-6Al-4V alloy. Thermo-calc simulated phase diagram was used to decide at.% of Ni to be added to aerospace grade Ti-6Al-4V alloy. It found that adding 5% of Ni promotes grain refinement without forming C14 Laves phase and increasing the β-transus temperature. Optimum values of μ-plasma power and μ-plasma torch travel speed were identified by manufacturing single-layer depositions of Ti-6Al-4V-5Ni alloy thorough diluted depth, aspect ratio, deposition quality, deposition geometry, and deposition efficiency as the criteria to manufacture its multi-layer deposition. Results reveal that inclusion of nickel to Ti-6Al-4V alloy increased the volumetric percentage of β-Ti phase from 13 to 27% and refined grains of α-Ti and β-Ti phases which improved yield and ultimate tensile strength of Ti-6Al-4V-5Ni alloy by 13.4% and 17.8% respectively and reduced % elongation by 36% as compared to Ti-6Al-4V alloy. It changed fractured pattern from ductile to combined ductile and brittle fracture consisting of cleavage facets, voids, and larger size dimples. It increased % porosity, microhardness, fracture toughness, and abrasion resistance thus imparting Ti-6Al-4V-5Ni alloy more resistance to crack initiation and more restriction to movement of the dislocations. Vanadium and nickel contents in β-Ti phase of Ti-6Al-4V-5Ni alloy are 3 to 5 times and 21 to 25 times more than that its α-Ti phase, respectively. Findings of this work demonstrate that μ-PBMAM developed Ti-6Al-4V-5Ni alloy is useful for high temperature, high strength, and light weight applications in aerospace, space, automobile, and dies and mold industries due to promotion and grain refinement of β-Ti phase, improvement in microstructure, microhardness, yield and tensile strength, fracture toughness, abrasion resistance. [ABSTRACT FROM AUTHOR]

Large-scale industrial application of additively manufactured (AM) components in general, and specifically cold sprayed additive manufactured (CSAM), is limited due to the nature of this technology and the resulting product's porosity and embrittlement. To improve the final properties of additively manufactured material, many lengthy, complex, or expensive post-treatments have been proposed. Reducing the environmental impact, cost, and time required for additive manufacturing will allow for greater use in industrial applications. A novel thermomechanical treatment known as in situ electro-plastic treatment (ISEPT) is used in this study to treat CSAM Ti-6Al-4 V alloy known as grade 5 titanium. The Ti-6Al-4 V alloy has approximately three times the strength and hardness of commercial purity titanium (CP-Ti) with lower ductility and a dual-phase (α + β) microstructure that poses challenges during the CSAM process. Compared to CP-Ti, the results showed that CSAM Ti-6Al-4 V presented double the porosity and triple the number of ISEPT passes that presented ~ 2 µm ultra-fine grain microstructure. The ultimate tensile strength (UTS) of the ISEPT material was superior to that of CSAM Ti-6Al-4 V and increased from 184 to 1096 MPa with improved ductility rise from 1.1 up to 8.8%. Six ISEPT passes in air resulted in a slight increase in oxygen from 0.2% in the as-CSAM condition to 0.35%. Tensile properties of the ISEPT material were comparable to wrought Ti-6Al-4 V with 989 MPa UTS and 8.3% elongation. The ISEPT passes consolidated the CSAM (α + β) dual-phase Ti-6Al-4 V and allowed for the nucleation of equiaxed grains at the vicinity of former CSAM splat boundaries. The formation of lamellar colonies within the splat's inner regions was observed. The role of ISEPT conditions on the rapid elimination of porosity and the evolution of cold spray splat boundaries via dynamic recrystallization were discussed. [ABSTRACT FROM AUTHOR]

This research aims to investigate the effects of as-casted and proposed in situ heat-treated squeeze casting of Al-3.5 % Cu alloy. The effects of squeeze pressure, melt temperature and die temperature on ultimate tensile strength, percentage elongation and hardness were modelled and analysed for as-casted and in situ heat-treated squeeze casting using the Box-Behnken design. Response surface methodology was used for experimental design, empirical modelling and analysis. Adequacy and validation of the developed models were verified using ANOVA and confirmation experiments, respectively. The results revealed squeeze pressure as the most significant input variable followed by die temperature under as-casted and in situ heat-treated squeeze casting conditions. The comparative analysis suggested in situ heat-treated squeeze casting conditions as the best alternative which resulted in 7.9~11, 6.7~25.7, and 2.2~7.7 % improvement for ultimate tensile strength, percentage elongation and hardness, respectively. A considerable increase in mechanical properties provided a great evidence to reveal a new technique for foundry men to enhance the quality of squeeze casted Al-Cu alloys. Furthermore, the empirical model will aid practitioners to predict the desired mechanical properties prior to examination. [ABSTRACT FROM AUTHOR]

This study investigated the print homogeneity of Ti-6Al-4 V alloy parts, when printed over a large build area of 250 × 250 × 170 mm3, using a production scale laser powder bed additive manufacturing system. The effect of part location across this large build area was investigated based on printed part porosity, microstructure, hardness, and tensile properties. In addition, a Hot Isostatic Pressing (HIP) treatment was carried out on the as-built parts, to evaluate its impact on the material properties. A small increase in part porosity from 0.01 to 0.09%, was observed with increasing distance from the argon gas flow inlet, which was located on one side of the build plate, during printing. This effect, which was found to be independent of height from the build plate, is likely to be associated with enhanced levels of condensate or spatter residue, being deposited at distances, further from the gas flow. Despite small differences in porosity, no significant differences were obtained for microstructural features such as prior β grain, α lath thickness, and phase fraction, over the entire build area. Due to this, mechanical performances such as hardness and tensile strengths were also found to be homogenous across the build area. Additionally, it was also observed based on the lattice constants that partial in-situ decomposition of α ′ → α + β phases occurred during printing. Post HIP treatment result showed a decrease of 7 and 6%, in the yield strength (YS) and ultimate tensile strength (UTS), respectively, which was associated with a coarsening of α lath widths. The potential of the laser powder bed system for large area printing was successfully demonstrated based on the homogenous microstructure and mechanical properties of the Ti-6Al-4 V alloy parts. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is a fabrication process based on the addition of material by layers and has shown several advantages against other manufacturing processes, such as low cost and possibility of manufacturing parts with complex geometries. However, the additive manufacturing can change the properties of the workpiece due to the strategy of multilayer deposition, which can cause changes in the microstructure of the deposited material. In this sense, this work aimed to evaluate the chemical composition, microstructure, and mechanical and electrochemical behavior of the 316L stainless steel manufactured by wire and arc additive manufacturing (WAAM), comparing it with a sample of the same alloy in the annealed condition, trying to understand how the different layers interfere in the final behavior of the material. The results indicate that the microstructure of the deposited material is different with the presence of ferrite in an austenitic matrix. Two regions whose microstructure had different morphologies were also identified in the WAAM alloy. In the region close to the fusion line between the deposited layers, the austenite grains are smaller, about 5 μm wide, against 10 μm of the grains in the area most to the center of the layers. This microstructural change caused an irregular microhardness profile, with an average of 276 HV, higher than the 190 HV of conventional material. It was also observed that the WAAM process caused a decrease in the yield strength (YS) (23%) and elongation (78%) of the alloy and a slight increase in the value of ultimate tensile strength (UTS) (9%); however, it still meets the minimum requirements for most industrial applications required for the material studied (min. UTS 485 MPa, min. YS 170 MPa, and min. elongation 35 MPa). Moreover, the electrochemical results in simulated seawater solution indicate that the corrosion potential of the deposited sample is like that of the conventional specimen (about 0.24 V), with the potential passivating of the first to be superior to that of the second, respectively, 0.640 V and 0.560 V. [ABSTRACT FROM AUTHOR]

As one of the important additive manufacturing techniques, selective laser melting (SLM) has shown great advantage in the production of metal matrix composite components with complex geometry. However, the layer-by-layer manufacturing procedure causes a nonnegligible thermal accumulation and cycling. Thus, the SLM-deposited component always presents gradient microstructure and mechanical properties. In this work, the dense TiB2p/2024Al composite prepared by SLM was employed to investigate the heat-induced microstructure evolution and mechanical properties. The as-deposited composite presents a uniform distribution of TiB2 reinforced particle in α-Al matrix with an oriented < 100 > texture α-Al dendrite microstructure. The yield strength (YS), ultimate tensile strength (UTS), and the elongation of as-deposited sample increase from 230.06 MPa, 302.52 MPa, and 4.49% to 244.17 MPa, 365.36 MPa, and 11.48% from the bottom to top regions. According to the TEM results, this phenomenon is attributed to the high cooling rate induced low content of θ-Al2Cu phase at the bottom of the sample. In addition, agglomeration of the TiB2 particles due to the insufficient convention is responsible to the poor elongation at the bottom of the sample. After the solid solution and aging heat treatment (T6), thanks to the uniform distribution of S strengthening phases, this gradient in microstructure and mechanical properties in the deposit can be eliminated, and the deposit presents higher YS, UTS, and a lower elongation of 380.23 MPa, 421.50 MPa, and 3.14%. [ABSTRACT FROM AUTHOR]

Al-Si alloys are increasingly being employed in the aerospace industry, satellite bearings, and inertial navigation systems. Hypoeutectic compositions are more attractive because of the low material cost and excellent castability. The addition of alloying elements to these alloys is generally used to modify the morphology of Si particles with a view to meeting mechanical strength requirements. Considering manufacturing requirements, to efficiently predict the quality of the machining process, it is essential to analyze the machinability of the material to be used, which depends on several factors, including microstructural features. In the present study, the effects of solidification cooling rate and Bi addition to Al-Si alloys on microstructural features, tensile properties, and rate of heat generation during necking processes are analyzed in samples of directionally solidified Al-9 wt% Si-(1.0 wt% Bi) alloy castings. The microstructure is composed of α-Al dendrites characterized by measured primary, secondary, and tertiary dendritic arm spacings, with a eutectic mixture of α-Al and Si-(Bi) particles. The addition of Bi is shown to attenuate the sharp tips of Si crystals. The dendritic length scale of the Al-rich matrix is correlated with the solidification cooling rate through experimental equations, and the evolution of the ultimate tensile strength with the primary dendritic spacing is experimentally represented by a single Hall-Petch-type equation for both examined alloys. Considering a same primary dendritic arm spacing, the addition of 1 wt% Bi to the Al-9 wt% Si alloy is shown to have the following effects: similar ultimate tensile strength, the elongation to fracture is improved, higher machinability based on significant decrease in the heating rate. [ABSTRACT FROM AUTHOR]

A statistical optimization based on experimental work was conducted to consider ultimate tensile strength (UTS) and elongation of dissimilar joints between AA5454 and AA7075 by friction stir weld (FSW). The goal of this work is to develop a comparative study of the optimization of FSW parameters using different orthogonal arrays, i.e., L12 and L16. Four parameters correlated to softening and forging requirements (rotational speed, traverse speed, tilt angle, and plunge depth), one parameter associated with the location of base metal in the dissimilar joint, and two parameters related to an FSW tool (pin profile and Dshoulder/dpin ratio) were considered and arranged in the employed arrays. Moreover, the investigation explored the microstructure and fractography of dissimilar joints and base metals by using optical and scanning electron microscopes. The results showed that the L16OA is more accurate than L12OA for the optimization of seven parameters due to the small statistical errors. For UTS, the errors range from 0.78 to 24% for L16OA and from 27.23 to 44.14% for L12OA. For elongation, the errors run from 11 to 12.9% for L16OA and from 33.77 to 49.73% for L12OA. The accuracies of generated models range from 50 to 99.5% for L16OA and range from 30.7 to 94.9% for L12OA. Tightening the levels (narrow domain) is the main reason for switching some optimum levels between both arrays. The highest UTS obtained is 221 MPa based on the optimum levels attained from L16OA, and the highest elongation is 12.83% according to the optimum levels acquired from L12OA. Despite the deficiency of effective intermixing, the study revealed that FSW acceptably could assemble joints between AA5454 and AA7075, presenting the proficiency of FSW with welding dissimilar aluminum alloys. [ABSTRACT FROM AUTHOR]

The laser-based powder bed fusion of metals (PBF-LB/M) offers a variety of advantages over conventional processing techniques and the possibility to recycle and reuse powder increases its sustainability. However, the process and resulting part properties are influenced by a variety of factors including powder recycling grade and residual oxygen content of the process atmosphere. Especially in terms of reactive materials like Ti-6Al-4V, oxidation during processing and recycling determines process stability and reproducibility. This work therefore focusses on the influence of the conventionally varied processing parameters as well as atmosphere residual oxygen content process and powder recycling on the microstructure and mechanical properties. For this purpose, the design of experiments approach is used and by evaluation of regression models, effect sizes and interactions are given. Additionally, two different etching techniques were employed to reveal different aspects of the microstructure. While no significant influence of powder recycling and residual oxygen on the microstructure could be observed, they both significantly influence the mechanical properties. A maximum hardness of 470 HV0.1, a maximum ultimate tensile strength of 1252.3 MPa, and a maximum elongation at break of 17.8 % were obtained. The results demonstrate the importance of the processing atmosphere's residual oxygen content and of taking into account the changing powder characteristics during recycling as well as its effect on the part properties. [ABSTRACT FROM AUTHOR]

This paper studied the combined effects of matrix-to-reinforcement particle size ratio (PSR) and SiC volume fraction on the mechanical properties of extruded Al-SiC composites. A powder metallurgy technique (PM) of cold pressing at 500 MPa followed by hot extrusion at 580 °C was adopted to produce Al/SiC composite. Aluminum powder of size 60 μm and silicon carbide with different sizes, i.e., 50, 20, and 8 μm, were used. Three different volume fractions of SiC were employed, i.e., 5, 10, and 15 %, for each investigated size using a constant extrusion ratio of 14.36. The effect of matrix-to-reinforcement PSR on the reinforcement spatial distribution, fabricability, and resulting mechanical properties of a PM-processed Al/SiC composite were investigated. It has been shown that small ratio between matrix to reinforcement particle size resulted in more uniform distribution of the SiC particles in the matrix. As the PSR increases, the agglomerations and voids increase and the reinforcement particulates seem to have nonuniform distribution. In addition, the agglomerations increased as the volume fraction of the SiC increased. It has also been shown that homogenous distribution of the SiC particles resulted in higher yield strength, ultimate tensile strength, and elongation. Yield strength and ultimate tensile strength of the composite reinforced by PSR (1.2) are higher than those of composite reinforced by PSR (7.5), while the elongation shows opposite trend with yield strength and ultimate tensile strength. [ABSTRACT FROM AUTHOR]

Mechanical properties and tensile fracture behavior of normal 7075 aluminum alloy produced by rheoforming were investigated. The rheoforming applies limited angular oscillation (LAO) technique for semi-solid slurry preparation and rheological squeeze casting with transverse moving injection feed semi-solid slurry. The microstructures of as-cast rheoformed 7075 alloy are composed of fine spherical α-Al grains with average size of 26 μm surrounded by eutectic mixture. T6 heat treatment (solution treatment for 4 h at 838 K (465 °C) and aging for 12 h at 393 K (120 °C)) causes a slight increase of grain size and the formation of fine semi-coherent precipitation of η′ phase in α-Al matrix. Good elongation to fracture (10.1%, which is quite close to the wrought target (11%)) is obtained for rheoformed 7075 alloy after T6 heat treatment, with average yield strength of 461 MPa and average ultimate tensile strength of 514 MPa. Pores and voids are main defects observed in rheoformed 7075 alloy. The fracture surface of as-cast rheoformed 7075 alloy consists of large and deep dimples showing the growth and coalescence of voids. After T6 treatment, the fracture surface is composed of large dimples, flat areas containing super-fine dimples and tear ridges. Pores are present in the form of large dimples in fracture surface. The crack initiates at pores and propagates by the coalescence of pores and voids. [ABSTRACT FROM AUTHOR]

The switchback deposition strategy is a unique approach where the torch is moving cyclically forward and backward for preventing the unidirectional grain growth in wire + arc additive manufacturing (WAAM). Experiments were conducted for comparing the walls deposited in bidirectional and switchback strategies. The travel speed, inert gas flow rate, and number of deposited layers were kept constant for both the conditions. The grain growth behavior was identified from the bottom to top and welding direction. Finally, samples were extracted from the walls for mechanical property analysis and microstructural studies. Switchback mode produces ~ 70% γ′-phase whereas the bidirectional mode has ~ 77% γ′-phase in the matrix. Inconel 625 sample deposited using switchback technique revealed ~ 10-µm lesser primary dendritic spacing in the middle region and the standard deviation of overall structure is ~ 5 µm less compared with bidirectional deposition resulting in relatively higher average hardness. The switchback mode also results in ~ 2 µm lesser average secondary dendrite size among both the deposition strategies. The switchback deposition mode displayed a higher average yield strength (σy) (~ 440 MPa) than the bidirectional mode (~ 390 MPa) and approximately identical ultimate tensile strength (σu) with a 20-MPa variation. [ABSTRACT FROM AUTHOR]

In this research, copper (Cu) donor material-assisted friction stir welding (FSW) of AA6061-T6 alloy was studied. Cu-assisted FSW joints of AA6061-T6 alloy were prepared at a constant tool rotational rate of 1400 rpm and various welding speeds at 1 mm/s and 3 mm/s. The Cu donor material of different thickness (i.e., 20%, 40%, and 60%) with respect to the workpiece thickness was selected to assist the FSW joining at the plunge stage. It is observed that the downward force generated in the FSW process was gradually decreased after introducing Cu donor material with incremental thicknesses with respect to workpiece at the plunge stage. Post-weld analysis was characterized in terms of microstructure and mechanical properties. The results of microstructure analysis at the stir zone (SZ) show the formation of finer grains due to dynamic recrystallization and plastic deformation. Micro-hardness tests reveal that the hardness decreased from the base metal (BM) to the SZ across the heat-affected zone (HAZ) and thermo-mechanically affected zone (TMAZ). The lowest value of hardness appeared in the TMAZ and HAZ where tensile failure occurs. With increasing welding speed, the average hardness in the SZ decreased due to lower heat input and faster cooling rate. Tensile test plots show no significant change in ultimate tensile strength with or without Cu donor material. Fractography of tensile tested samples shows both ductile and brittle like structure for given welding parameters. This proposed work of FSW with Cu donor material is promising to increase tool life due to the decrement of the downforce during plunge and throughout the welding stage. Meanwhile, the inclusion of donor material did not compromise the weld quality in terms of the mechanical properties and micro-hardness. [ABSTRACT FROM AUTHOR]

This investigation aims to make clear the relationships among geometric features, macrostructures, microstructures, and mechanical performances of the weld bead in the gas metal arc welding (GMAW) process for ASTM A606 type IV weathering steel. The results indicate that with the increase of welding heat input, the geometry of the top reinforcement and penetration increases proportionally until reaching the peak value, and then declines with the further increase of welding heat input; while the values of bottom reinforcement increase continuously with the increase of welding heat input. The average ultimate tensile strength (F), maximum displacement (L), and failure energy (E) of the welded joint produced by the moderate welding heat input are 10.27 kN, 1.88 mm, and 13.55 J, respectively, which are obviously larger than those obtained by the insufficient welding heat input (F: 8.33 kN, L: 1.20 mm, and E: 7.10 J). Although the mechanical properties of the welds achieved by the overlarge welding heat inputs present comparable levels (F: 9.73 kN, L: 1.86 mm, and E: 13.51 J), their standard deviation is much higher. Acicular ferrite, grain boundary ferrite, side plate ferrite, Widmanstätten ferrite, and pearlite are noticed in the fusion zone (FZ), while the coarse grain heat-affected zone (CGHAZ) is composed of upper and lower bainite, grain boundary ferrite, Widmanstӓtten ferrite, polygonal ferrite, and pearlite. As the welding heat input increases, the pre-austenite grain width in the FZ and CGHAZ decreases. The descending order of the microhardness distributed in the welded joints is fusion line, CGHAZ, FZ, fine grain heat-affected zone (FGHAZ), and base metal. In addition, the microhardness values of FZ and CGHAZ decline with the rise of the welding heat input. Nonetheless, no apparent links are found between the microhardness levels of the FGHAZ and welding heat input. [ABSTRACT FROM AUTHOR]

The hydro-assisted tube pressing (HATP) process is a new severe plastic deformation method that is proposed in this paper to improve the mechanical properties of long tubes. The pressured fluid between the tube and die eliminates the friction force between the tube and die and, thereby, decreases the required forming force. This facilitates the production of high-strength relatively long tubes. In the current study, this process was applied to a commercial pure copper tube during six passes at room temperature. Then, the hardness, tensile and electrical properties, and also microstructure of the samples were investigated. With increasing the number of passes, the grain size of the copper tube decreased. After two passes of the HATP process, the values of yield strength and ultimate tensile strength increased from 150 and 223 MPa to 347 and 366 MPa, respectively, and the total elongation decreased from 32 to 10%. After four passes, the tube hardness significantly increased from 81 to 132 HV, and a homogeneous distribution of hardness was obtained along with the tube thickness. The electrical conductivity of the copper tube decreased by 3% after two passes. Also, the effective plastic strain and the required processing force were investigated using the Abaqus commercial finite element software. It is concluded that the required force and the strain distribution are independent of the tube length. The hydro-assisted tube pressing method potentially can be used in the industrial production of long tubes with high mechanical strength and electrical conductivity. [ABSTRACT FROM AUTHOR]

In this work, the effect of material location and tool deviation on global and local mechanical behavior of dissimilar AA2024/AA7075 friction stir weld joints was investigated. The results showed that increasing the tool deviation value up to 1 mm towards the soft material, fixed in the advancing side, improved the material mixing quality and enhanced the grain refinement in the stir zone. It was found that the highest ultimate tensile strength was obtained when the AA7075 alloy was fixed in the retreating side for 1-mm tool deviation towards the AA2024 alloy. Above this deviation value, a gradual decrease of the global mechanical properties of the weld joints was noticed. The digital image correlation (DIC) technique coupled to tensile testing revealed an improvement of local strain in the stir zone as well as the heat-affected zones of the dissimilar joints when the AA2024 alloy was positioned in the advancing side. [ABSTRACT FROM AUTHOR]

The effects of process parameters on microstructure and mechanical properties of the 316L stainless steel helical micro-diameter spring (316L HMDS) fabricated by selective laser melting (SLM) were explored. By optimizing SLM process parameters, the near-full density (> 99%) SLM-316L HMDS can be manufactured. The SLM-316L HMDS exhibits typical layered morphology consisting of micron-sized melt pools and columnar grains whose growth orientations are consistent with the temperature gradient. Lower hatch space reduces the formation of voids, resulting in better density, elongation, and ultimate tensile strength of the SLM-316L HMDS. The form angle significantly affects the yield strength and ultimate tensile strength, and obvious dimples appear on the fracture surface, demonstrating toughness fracture. The experimental results establish the correlation between the process parameters of SLM and the microstructure and macro-mechanical properties of the SLM-316L HMDS. [ABSTRACT FROM AUTHOR]

In many applications, in the aerospace and other industries, acquiring a high-quality weld is challenging using conventional joining techniques especially for materials with low melting temperatures. Friction stir welding (FSW) is a high-quality solid-state joining technique for welding lightweight materials. However, there is a need to prevent the transfer of excessive heat into the weld zone and to have a steady-state heat flow at the FSW tool. Therefore, significant research is being conducted to find an effective coolant-lubricant for FSW. More recently, interest has increased in the possibility of replacing traditional lubrication methods with effective and more sustainable alternatives. The present study investigates the effect of minimum quantity lubrication (MQL) on the microstructure and mechanical properties of FSW aluminum alloy 6061-T651. Friction stir welding tool forces, tensile strength, and microstructure characterization were conducted on FSW Al 6061 samples produced using feed speeds from 100 to 260 mm/min and spindle speeds of 1000 to 2200 rpm. The results showed that MQL as a near-dry lubricant could reduce the measured forces during the FSW process. Most importantly, the results demonstrate that the average ultimate tensile strength (UTS) of the joints increased and the grain size area decreased with the use of MQL as compared to the dry process joining. The finest grain size area obtained was 6 μm2 using a spindle speed of 1600 rpm at a feed speed of 180 mm/min with MQL applied. [ABSTRACT FROM AUTHOR]

2D-C/Al composites were prepared by liquid extrusion infiltration under the different extrusion temperatures of 570, 585, 600, 615, and 630 °C of infiltration mold. Through the observation and analysis of the microstructure and ultimate tensile strength (UTS) of the composites, it showed that extrusion temperature had important influence on the infiltration effect and tensile property of 2D-C/Al composites. When the extrusion temperatures were 570 and 585 °C, very few aluminum alloy liquid was filled into the carbon fiber preform, and the UTS(s) of composites was low. When the temperature reached 600 °C, infiltration effect and UTS had been improved. With the increase of extrusion temperature at 615 °C, the infiltration of aluminum alloy liquid was sufficient, the distribution of carbon fibers was uniform, and defects of casting holes and fiber damage could not be found. UTS had been improved 115.8% more than that of the matrix. However, when extrusion temperature reached 630 °C, infiltration of the alloy was sufficient, but there was fiber damage, which would reduce the UTS of the composites. The increased proportion of UTS was only 21.7%, and this was not satisfied. Through comparison and analysis, 615 °C was a better extrusion temperature than others, and infiltration effect and UTS were more satisfied. It was adverse for preparing ideal 2D-C/Al composite to have too low and too high extrusion temperatures. [ABSTRACT FROM AUTHOR]

Pulsed magnetic field (PMF) was successfully applied during direct chill (DC) casting of 6063 Al alloy. The effect of PMF on the solidification structure and mechanical properties was investigated. The results indicated that the coarse equiaxed grain turns into homogeneous and refined equiaxed grain under the effect of PMF, and the grain refinement effect increases with increasing the input current in the study. This can be attributed to the reduced temperature gradient in the melt and enhanced heterogeneous nucleation caused by forced convection, based on the simulation results of Lorenz force, flow field, and temperature field during DC casting under PMF. The application of PMF can also efficiently reduce the macro- and microsegregations of Mg and Si elements, which are beneficial to the uniformly dispersed precipitation of MgSi phase after T6 treatment, resulting in a significant enhancement of strength and hardness. The best mechanical properties of the 6063 Al alloy are achieved under PMF with an input current of 500 A, exhibiting the increments of 35.6% in hardness, 42.2% in ultimate tensile strength, and 30.6% in elongation, respectively. This study may offer a promising method for industrial preparation of high-quality alloys by DC casting. [ABSTRACT FROM AUTHOR]

AA5754/AA7075 was butt-welded by friction stir welding, and the joint of each weld case was identified by ultimate tensile strength, percentage of elongation, and hardness. Moreover, the significance of each parameter was investigated, and a mathematical relation was constructed by regression analysis. A defect-free joint was achieved in the case of a weld produced with 1000 rpm of tool rotational speed, 80 mm/min of welding speed, and an 22-mm tool shoulder diameter. Most of the failures are located at the bottom of the pin and side of AA7075. The ultimate tensile strength (UTS) decreases with increasing welding speed (WS) or increasing tool rotational speed (TRS). Hardness distribution in the weld zones varied dependent on the nugget zone formation affected by TRS and WS. The present study also investigated the significance and contribution of each parameter on the UTS by analysis of variance (ANOVA). From the results of ANOVA, the conclusion reached is that the all the parameters have a great influence on UTS. The contributions are 41.41 % for WS, 17.58 % for diameter, and 13.28 % for TRS. Moreover, a full quadratic model was constructed between the parameters and the UTS value. The results show that the variation from the predicted values was between 0.41 % and 10.36 %. The strength of the model was analyzed by R-Sq. The achieved R-Sq is 0.892, which means that there is a strong relation between predicted and actual values. [ABSTRACT FROM AUTHOR]

The success of laser-foil-printing (LFP) additive manufacturing depends critically on the laser welding of sheet metals onto the substrate or the previous layer during the part fabrication process. The welding can be generally categorized into two modes: conduction mode and keyhole mode. In this study, 304L stainless steel parts fabricated by the LFP process using the two laser welding modes are compared. The porosity, microstructure, and tensile properties of the fabricated parts in these two modes are measured and compared in the laser scanning direction (X) and part building direction (Z). The parts fabricated in the conduction mode have a higher density than those fabricated in the keyhole mode. On the tensile properties, both yield strength (YS) and ultimate tensile strength (UTS) have insignificant differences statistically based on the ANOVA analysis between the tensile specimens fabricated with the two welding modes by the LFP process. However, the conduction-mode parts have higher elongation than the keyhole-mode parts in both the X and Z directions, and the difference is especially significant in the Z direction. By using the electron backscattered diffraction (EBSD), it was found that the much higher ductility for the conduction-mode parts in the Z-axis direction is mainly due to the distinct grain boundary interface density in the Z-axis direction between the two welding modes. [ABSTRACT FROM AUTHOR]

Cylindrical parts with inner ribs (CPIR) of magnesium alloy have increasingly become a research focus to adapt the continuous improvement of lightweight requirement. The hot power spinning (HPS) method was proposed to form the magnesium alloy CPIR, and the microstructures, textures, and mechanical properties of blank and spun workpiece at cylindrical wall (CW) and inner rib (IR) were analyzed experimentally. The results show that the average grain size at CW and IR of spun workpiece is refined from 2.49 μm of blank to 1.88 μm and 2.11 μm, respectively. The c-axis of most grains at CW and IR of spun workpiece is deflected from tangential direction (TD) to radial direction (RD) by 90° and 72°, respectively. Compared with blank, the elongation at CW and IR of spun workpiece is increased by 52.2% and 39.8%, respectively. The yield strength and ultimate tensile strength of IR are basically the same as those of blank, while those of CW are decreased by 6.5% and 3.9%, respectively. The difference of macro fracture directions of tensile specimen of blank and spun workpiece is resulted from the change of grains c-axis direction and the increase of grain freedom degree around c-axis. [ABSTRACT FROM AUTHOR]

The effects of heat treatment on the microstructures and mechanical properties of tungsten inert gas-welded AZ31 magnesium alloy joints with CrO flux coating were investigated by microstructural observations, microhardness, and tensile tests. The results showed that the activating flux of CrO improved the weld penetration and the depth/width ratio of the tungsten inert gas-welded AZ31 magnesium alloy joints markedly. Heat treatment (1) eliminated the coarsened network-like β-Mg(Al, Zn) particles which formed in activating tungsten inert gas and (2) resulted in more uniform grain size distribution of partially melted zone. Apart from that, either the microhardness of the seams, the ultimate tensile strength, or the elongation of the welded joints was improved by aging treatment, while too high aging temperature would give rise to a sharply decreased ultimate tensile strength. [ABSTRACT FROM AUTHOR]

Aluminum matrix composites (AMCs) are among the advanced materials that are employed in numerous industrial applications. AMCs have good stiffness and strength. They have low weight that makes them valuably handy for improving fuel efficiency and economy in the structures made from them. The friction stir processing (FSP) is a novel technique which is highly advantageous for producing composites, which are reinforced with particles that are sub-micron in size particularly in light weight metal matrix composites (MMCs). Current study is done to examine the potential of AA6061-based surface nanocomposites by reinforcing it with carbon nanotubes (CNTs) (as-received and purified) employing FSP. Fabrication of the composites is carried out by filling CNTs into the grooves of different sizes and friction stir processed (FSPd). Various parameters are investigated to attain best mechanical properties and dispersion of CNTs in the matrix. Metallography is used to reveal the material flow and grain size variation in the zones formed by the FSP. Micro hardness and tensile tests are conducted to evaluate the mechanical properties and an increase of 47.3% hardness and an increase of 32.4% ultimate tensile strength (UTS) are observed from the base FSPd material. Electron microscopic techniques are also employed to reveal the microstructural details. [ABSTRACT FROM AUTHOR]

Tool wear study is undertaken with IS 3039, grade II steel plates and analysed by two modes of the metal transfer phenomenon. The first mode of metal transfer takes place by the direct contact of the tool shoulder on the work plate, generating heat owing to friction, and the second mode of metal transfer takes place around the pin. This study is aimed at knowing the formation of a weld for every 300-mm length, which indirectly reflects the effect of the pin profiles on producing a better weld. The individual contribution of two modes of metal transfer has been studied, and it was observed that the higher the area of the first mode of metal transfer, the more the strength of the weld. The variations in the distribution of hardness along the first mode of metal transfer were found to be higher, because the compaction offered by the tool shoulder is more than that in the second mode of metal transfer. Microstructure and macrostructural analyses were performed on the weld, based on the two modes of the metal transfer phenomenon. The ultimate tensile strength gets reduced, if the percentage formation of the first mode of metal transfer is less. [ABSTRACT FROM AUTHOR]

In this study, the effects of tool rotational and traverse speeds on the mechanical properties and the microstructure of the friction stir welded joints from Al 5086-H34 were studied. Insufficient heat generation and inadequate metal transportation at very low rotational speed and high turbulence in the plasticized metal at very high rotational speed emerged tunnel and worm hole defects into the weldment. It was discovered that as rotational and traverse speed increased, the average grain size of the weldment decreased due to more dynamic recrystallization and amplified stirring effect. An increase in the rotational speed increased the ultimate tensile strength and microhardness of the specimens. At the best welding condition, by employing the rotational and traverse speeds of 1250 rpm and 80 mm/min, respectively, 51 % enhancement in the elongation and 8 % increase in the microhardness of the welded samples were obtained. Moreover, the ultimate tensile strength of this welded joint reached to 85 % of the base metal. [ABSTRACT FROM AUTHOR]

Asymmetrical thermomechanical rolling (ATMR) process of API X70 microalloy steel was investigated to evaluate of rolling force and distribution of material property in the roll gap. Applying a user-defined VUMAT subroutine, the equations of material flow and microstructure kinetics, as material genome package, were implemented into finite element (FE) solver of ABAQUS for simulation of X70 multi-pass rolling. A rough rolling schedule was carried out to verify the accuracy of the material genome by evaluation of the computed rolling force of FE model and experimental results. Considering the interaction of the asymmetrical parameters such as rolls speed ratio (VA), pass height (PH) and rolls diameter ratio, it was found that coinciding of the high level PH with high range of rolls speed ratio and diameter ratio lead to a rise of the rolling force. Strain distribution of the roll gap indicated that an increase of the rolls speed ratio can improve the dislocation density and the strength of rolled material. The study of strain distribution contour in the length of slab thickness revealed that the homogeneity of deformation can be enhanced in the mechanism of asymmetrical rolling of microalloy steel. Experimental test reveals that in asymmetry condition in TMR process of X70, increase of the speed ratio (1.02-1.05) in roughing passes leads to a considerable grain refinement and growth of yield strength and ultimate tensile strength of 3.12 and 2.05% of final plate structure, respectively. [ABSTRACT FROM AUTHOR]

In this work, Cu-15Ni-8Sn components were manufactured by selective laser melting (SLM) with a near full density of about 99.4%. The microstructures and phase precipitation of the as-fabricated Cu-15Ni-8Sn alloy were characterized by X-ray diffraction (XRD), electron probe microanalyzer (EPMA), electron back-scattered diffraction (EBSD), and transmission electron microscope (TEM). It was demonstrated that the as-fabricated Cu-15Ni-8Sn alloy shows α-phase with γ-precipitates by XRD and TEM. The size of the grains of α-phase is in the range of 5~20 μm with random orientation distribution. The γ-precipitate is a Sn- and Ni-rich phase distributed dispersedly in matrix and accumulatively in grain boundary. The as-fabricated Cu-15Ni-8Sn alloy exhibited yield strength of 522 MPa, ultimate tensile strength of 653 MPa, and elongation of 17%. The excellent mechanical performance of the as-fabricated Cu-15Ni-8Sn alloy is caused by the local laser melting mode including rapid cooling rate and reduplicative fusing from the subsequent layer melting, which leads to refined grains and limited Sn segregation in micron-size within the matrix. [ABSTRACT FROM AUTHOR]

The microstructure, mechanical properties, and strengthening mechanisms of an Al-Mg-Si alloy (AA6060) subjected to severe plastic deformation using equal channel angular pressing (ECAP) were investigated. Samples were passed through a die with an inner angle of Φ = 90° and outer arc of curvature of Ψ = 37° at room temperature up to 12 passes via route Bc. Electron backscatter diffraction (EBSD) was used to evaluate the microstructure and misorientation boundaries. The microstructure showed a large fraction of low-angle boundaries associated with subgrain formation in the first ECAP pass, while after eight and 12 passes, a heterogeneous ultrafine grain structure with an average grain size around 0.57 and 0.47 μm, respectively, was obtained. In order to characterize the mechanical properties, microhardness and tensile tests were carried out. Results of mechanical property tests show that microhardness, yield stress, and ultimate tensile strength increase as ECAP pass number increases up to a maximum value of 120 HV, 344 MPa, and 355 MPa, respectively, after five passes. The Hall-Petch effect, dislocation, solid solution, and precipitation strengthening were evaluated to determine the dependence of the yield stress on the ECAP pass number. The results show that the strength effect arises from the subgrain microstructure rather than from the highangle grain boundaries developed. [ABSTRACT FROM AUTHOR]

The isothermal forging of a cast Mg-5.89 wt.% Zn-0.79 wt.% Y-0.32 wt.% Zr magnesium alloy was carried out to form the tank cover. The forming process of isothermal forming is studied by finite element model simulation and experiment. Based on the optimum isothermal forging process, the isothermal forging experiments of the cast Mg-Zn-Y-Zr magnesium alloy tank cover were successfully conducted. The results show that the experimental results such as forming load are in good agreement with the calculated ones. The tank cover forging with complete die fill and without fold defect can be obtained by utilizing the optimum isothermal forging process. The mechanical properties of the tank cover show a significant improvement over those of original materials, and the tank cover exhibits an ultimate tensile strength of 302 MPa, a yield strength of 209 MPa, and an elongation of 13%. [ABSTRACT FROM AUTHOR]

A complex experimental study of laser welding of the V-1469 Al-Cu-Li alloy is performed for obtaining a high-strength welded joint. The phase composition, microhardness, and strength characteristics of the alloy and welded joint in various regimes of heat treatment are studied. It is found that heat treatment of the welded joint increases its ultimate tensile strength. After complete heat treatment, microhardness values of the alloy and the welded joint become close to each other. Standard heat treatment of samples after welding allows recovery of the structure and phase composition of the entire sample at the micrometer size level. The use of heat treatment allows one to obtain the welded joint strength equal to 0.85 of the base alloy strength in the as-received T1 state. [ABSTRACT FROM AUTHOR]

The present study has investigated the influence of calcium process control agent on the microstructure and mechanical properties of powder metallurgy processed samples fabricated by milling and spark plasma sintering technique. The microstructure of spark plasma sintered Ti-6Al-4V with 0.3 wt% Ca (Ti-6Al-4V-0.3Ca-M) samples revealed fine grain structure compared to sintered unmilled (Ti-6Al-4V-UM) samples. The average grain size values of sintered Ti-6Al-4V-0.3Ca-M and Ti-6Al-4V-UM samples are 8 and 60 μm, respectively. The spark plasma sintered Ti-6Al-4V-UM exhibited a yield strength (YS) of 875 ± 10 MPa, ultimate tensile strength (UTS) of 1057 ± 2 MPa, and % elongation (% El) of 15 ± 2. The spark plasma sintered Ti-6Al-4V-0.3Ca-M exhibited higher YS of 964 ± 9 MPa, UTS of 1153 ± 7 MPa, and lower % El of 6 ± 1 when compared to mill annealed Ti-6Al-4V alloy (YS 899 MPa, UTS 978 MPa and %El 15). The higher strength of Ti-6Al-4V-0.3Ca-M sintered samples could be attributed to the fine grain structure and the presence of interstitial elements in the matrix. In contrast, the lower strength of Ti-6Al-4V-UM can be ascribed to its coarse grains. [ABSTRACT FROM AUTHOR]

A series of experiments of high-power fiber laser-arc hybrid welding of pure copper was carried out. It could be seen that the microstructure of weld metal was obviously coarsened, and the columnar grain spacing at fusion zone and the massive grain size at heat-affected zone were both linearly increased with the increase of heat input. The weld conductivity decreased with the increase of heat input because the widening weld increased the microstructure nonuniformity of test samples. The heat input as well as welding parameter has no obvious effect on the ultimate tensile strength (UTS) of cross-weld but has obvious effect on the elongation. The UTS of all the welds was 200 MPa or so. The elongation was bigger than 20% when the heat input was in the optimization range from 250 to 380 J/cm. The decrease of the elongation was attributed to either high porosity at insufficient heat input or coarser grain at excessive heat input. [ABSTRACT FROM AUTHOR]

Mg-Al-Sn magnesium alloys have bright future in application because of good properties without rare earth elements. To study the effects of rotation rate on microstructures and mechanical properties of Mg-5Al-1Sn alloy after friction stir welding (FSW), extruded plates were butt welded by FSW with various rotation rates at constant other parameters. The results showed that after FSW, MgAl phase with poor thermal stability was dissolved, while MgSn phase remained due to high dissolution point and good thermal stability. The hole-type defects were observed at 600 rpm, and the weld joint was with no defects at 800~1100 rpm. The weld joint at 800 rpm gave a maximum ultimate tensile strength (UTS), which was 91% of the base material (BM). After FSW, both UTS and elongation of weld joints decreased compared with the BM, caused by the soften region between nugget zone (NZ) and thermo-mechanically affected zone (TMAZ), the dissolution of MgAl phases, the residual stress and dislocation content in the TMAZ, and the textural variation. With increasing rotation rate from 600 to 1100 rpm, the UTS of weld joints first increased and then decreased, while the elongation kept mostly unchangeable due to the common action of multifactors. [ABSTRACT FROM AUTHOR]

Four tools with taper (TA), triangular (TB), three-grooves (TC), and square (TD) pin-tip profiles were designed to friction stir weld (FSW) thick AA7075-T6 alloy plates aiming at improving the local and overall mechanical properties of the joints. The microstructure evolution, hardness, and mechanical properties of the FSW joints were studied by scanning election microscope (SEM), X-ray diffractometer (XRD), and transmission electron microscope (TEM). The results show that equiaxed grains in the bottom nugget zone (BNZ) obtained by using TC are noticeably refined compared to in the case of other tools. Also, finer and more dispersive precipitates are distributed in this BNZ, and higher contents of η phase and dislocations are observed. A similar trend is found in the middle of weld. The bottom slices welded by employing TC show superior strength and ductility with a highest ultimate tensile strength of 388 MPa, yield strength of 315 MPa, and elongation of 7.9 %, which are in agreement with the hardness profiles. This is owing to ultrafine grains, more high-angle grain boundaries, more dispersive and higher contents of precipitates, and optimum hardness distribution. Accordingly, the global mechanical properties of the overall joints prepared by using TC significantly improve. [ABSTRACT FROM AUTHOR]

Two-dimensional C/Al composites were fabricated by liquid-solid extrusion following vacuum infiltration technique (LSEVI), and defects were studied and analyzed through optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope(TEM), and the tests of ultimate tensile strength (UTS). Through research, it was found that gas impurities were the main factors to generate hole defects within the 2D-C/Al composites, so vacuum level of the test system should be higher than 0.09 MPa. The infiltration of composites would not be sufficient and uniform under the low squeeze pressure of 50 MPa and low squeeze temperature of 590 °C. However, when squeeze pressure was larger than 90 MPa, fiber damage appeared, and macro internal cracks even occurred if it was over 100 MPa. Poor tensile behavior of composites between carbon fibers and matrix might arise because of the inappropriate process parameters. Brittle tensile fracture of composites was observed under the higher preform preheating temperature of 640 °C, and AlC was found. Separated fibers and aluminum alloy of tensile fracture might occur under the lower preheating temperature of 580 °C. These defects hindered the improvement of property of C/Al composites greatly, and they should be avoided. Through contrast of UTS, internal cracks and poor tensile behavior were the most detrimental factors. Their UTSs were 45 and 117 MPa, respectively, which were less than 120 MPa of matrix. Improved process parameters were used to prepare the 2D-C/Al composite, and its defects were seldom found, so UTS of composite was improved 93.3 % than that of matrix. [ABSTRACT FROM AUTHOR]

Additive manufacturing is a powerful process to build complex geometry. Besides the numerous process parameters influencing the mechanical part performances, other parameters related to the initial powder feedstock or component machining are of most importance. In this study, the combined effect of a wide particle size distribution, surface machining and stress-relief heat treatment on the microstructure and mechanical properties (tension and fatigue) of a stainless steel AISI 316L, produced by laser powder bed fusion, is investigated. In order to correctly investigate those parameters separately, the netshape/machined character of the sample, alongside with the heat treatment, is studied for two kinds of powder having different particle size distributions, i.e. narrow and widely spread. Results show that a large spread of particle size is only slightly detrimental to the fatigue life, in particular in high-cycle conditions due to a larger porosity related to a weakly more uneven particle spatial distribution in the bed. Nevertheless, this effect is of a second order compared to machining or heat treatments which greatly affect the mechanical behaviour. Surface machining and moderate heat treatment are then the best post-operational steps to increase the fatigue life in high-cycle fatigue conditions independently of the particle size distribution. Results are discussed in terms of defects, microstructural modifications, surface roughness, martensitic transformation and mechanical loading. [ABSTRACT FROM AUTHOR]

Aluminum 6xxx and 7xxx series are among the most commonly used alloys in industrial applications whereas their joining and welding using conventional fusion-based weld processes are very difficult. In this paper, friction stir welding process of dissimilar AA6061-T6 and AA-7277-T6 aluminum plates was investigated. The effects of tool travers and rotational speeds and the type of material located in the advanced side (AS) or retreating side (RS) of weldment were studied experimentally on the mechanical and metallurgical characteristics of the joint. Macro- and microstructure pictures of weld region were used to evaluate the quality of the weld and defect detections. Tensile strength tests and micro-hardness measurements of different areas in the weld section showed that the most strength and hardness values are achieved when the AA-7277-T6 was located in the AS of the weld. Accordingly, the highest tensile strength was about 78 % of the ultimate strengths of AA6061-T6 base metal which was obtained at the rotational and linear speeds of 825 rpm and 60 mm/min, respectively. Most of the tensile fractures were initiated from the heat-affected zone (HAZ) of AA6061-T6 alloy. The minimum hardness values were obtained from HAZ for both alloys, and the average hardness of joint was reduced by increasing the rotational speed. Also it was observed from the microstructure analyses that the size of grains in the HAZ area was greater than that of the nugget zone. Using artificial neural network (ANN) approach, the hardness and ultimate tensile strength of tested AA6061-T6 and AA-7277-T6 aluminum joint was predicted for different friction stir welding (FSW) process variables including the pin speeds and material position on AS and RS. Also, using a multi-objective optimization technique, a Pareto front (or Pareto optimal set) was obtained for both hardness and tensile strength results. [ABSTRACT FROM AUTHOR]

In this study, 10-mm-thick pure copper plates were friction stir welded at a constant rotational speed of 700 rpm and different traverse speeds of 50, 100, 150, and 200 mm/min using a square pin profile tool. The thermal cycles and peak temperatures were recorded using accurate thermocouples. In addition, the microstructural features of the joints were examined by optical microscopy. Furthermore, for analyzing the mechanical performance of the joints, hardness and tensile tests were conducted. In addition, the fractography of the joints was done using a scanning electron microscope. The results showed that higher traverse speeds caused lower heat input and peak temperature and hence finer grains. Furthermore, higher traverse speeds lead to formation of the defects in the joints. With increasing the traverse speed, the ultimate tensile strength of the joints increased to a maximum value and then decreased. Likewise, with increasing the traverse speed, the hardness and elongation of the joints increased and decreased, respectively. Additionally, the joints welded at lower traverse speeds revealed more ductile fracture mode. [ABSTRACT FROM AUTHOR]

This paper presents an effect of friction welding parameters on the tensile strength and microstructural properties of dissimilar AISI 1020-ASTM A536 joints. A hybrid response surface methodology (RSM) and genetic algorithm (GA)-based technique were successfully developed to model, simulate, and optimise the welding parameters. Direct and interaction effects of process parameters on the ultimate tensile strength (UTS) were studied by plotting graphs. Friction force and friction time have a positive effect on tensile strength. As friction force and friction time increase, the tensile strength also increases. The maximum tensile strength of the friction-welded low carbon steel-ductile iron joints was 87 % of that of the base metal. The tensile properties, microstructure, Vickers hardness distribution, and fracture morphology of the welded specimen have been studied and presented in this study. Additionally, the distribution of carbon element on both sides of the interface was estimated using energy-dispersive spectroscopy (EDS). The results of the metallographic study show clearly that the friction welding process was accompanied by a diffusion of carbon atoms from ductile iron to steel. This process causes the formation of a carbon-rich zone at the interface and decarburization zone in the ductile iron close to the bond interface. [ABSTRACT FROM AUTHOR]

Two-millimeter-thick 2060 Al-Li alloy plates were friction stir welded under a welding speed of 95-150 mm/min and rotation speed of 750-1500 rpm. The effects of welding speed and rotation speed on formation quality, microstructure, secondary phase particles' transformation, and mechanical properties of the joints were investigated. The results show that defect-free joints are produced for varying friction stir welding (FSW) parameters, and nugget size increases firstly and then decreases with increasing rotation speed or decreasing welding speed. The weld nugget zones (WNZs) have fine dynamically recrystallized grains, and the size decreases to 7.9 μm with increasing rotation speed to 1180 rpm or decreasing welding speed to 118 mm/min, while the grains are coarsened at 1500 rpm or 95 mm/min. A similar trend occurs in the transformation of secondary phase particles, whose size is the smallest in WNZ at 1180 rpm-118 mm/min. All joints exhibit softened zones where the hardness is the lowest, and the joints fracture from WNZs or heat-affected zones. The joints welded at 1180 rpm-118 mm/min perform the highest ultimate tensile strength of 495 MPa, yield strength of 380 MPa, and elongation of 10.2 %. With increasing rotation speed or decreasing welding speed, the strengths and elongation of the joints increase firstly and then decrease. [ABSTRACT FROM AUTHOR]

The 7020-T6 aluminum alloy plates of 4 mm thickness were friction stir welded at rotational speeds of 400, 600, 800, and 1000 rpm and constant traverse speed of 100 mm/min. The peak temperatures of the joints were recorded by precise thermocouples. Microstructure, hardness, tensile properties, and fracture surfaces of the joints were analyzed. The results showed that decreasing the tool rotational speed from 1000 to 400 rpm decreased the peak temperature from 311 to 209 °C, and hence caused a lower heat input. In addition, lower rotational speeds result in higher hardness and tensile strengths. The higher hardness and ultimate tensile strength were related to the grain boundary, precipitation, and substructure strengthening mechanisms. In addition, the fracture surfaces of the joints welded at higher heat input conditions showed more ductile mode in comparison with that of welded at lower heat input condition, which confirmed the lower tensile elongation of the joints welded at lower rotational speeds. [ABSTRACT FROM AUTHOR]

A comprehensive investigation into processing-microstructure-property relations for optimization of ultimate tensile strength (UTS) of friction stir welded aluminum 6061 plates is presented. A customized experimental setup has been employed to measure temperature at multiple points of welded plates as well as the friction stir welding (FSW) tool axial force, transverse force, torque, and temperature under various combinations of process parameters. After performing a set of FSW tests based on a full factorial design, X-ray and ultrasonic tests were employed to detect process-induced failure in test samples. Using design of experiments, the main effects and percentage contributions of the process parameters on the maximum UTS were then identified. During the latter analysis, a new methodology is proposed to cope with the effect of 'variable' axial force, as it is often uncontrollable during FSW tests. Samples with the highest and lowest UTS were selected and examined in more detail by comparing their fracture surfaces using scanning electron microscopy (SEM), as well as their grain size distributions using electron back scattered diffraction (EBSD) and microhardness experiments. Finally, through the observed microstructure, temperature distribution, and welding force, it could be explained why the UTS and microhardness are found to notably vary between sample sof different RPM and weld speeds. [ABSTRACT FROM AUTHOR]

In a few last decades, equal-channel angular pressing (ECAP) has been one of the most prominent procedures for fabrication of ultrafine-grained (UFG) structures among various severe plastic deformation (SPD) techniques. The objective of this paper is to experimentally investigate the influence of longitudinal ultrasonic vibrations on the ECAP process. A robust experimental ECAP system was designed and manufactured, in which the punch can be excited by ultrasonic vibrations. ECAP experiments were carried out with and without ultrasonic vibration on pure Al. The microstructure of the specimens formed with ultrasonic-assisted ECAP and conventional ECAP were studied. The results of this study showed that superimposing ultrasonic vibrations on the ECAP process could improve the grain refinement efficiency. The grains of the specimens after conventional ECAP process were refined to 45 μm, while by applying ultrasonic vibration with amplitudes of 2.5 and 5 μm, the grains were refined to 28.2 and 22 μm , respectively. Using higher vibration amplitudes caused more refinement of the grains. The homogeneity of the microstructure after four passes of ECAP was also improved by 26.7 % while using ultrasonic vibration with amplitude of 2.5 μm. Higher vibration amplitudes made a more homogenous structure. The yield strength and ultimate tensile strength of the specimens after one pass of ECAP were higher in comparison with the conventional ECAP. [ABSTRACT FROM AUTHOR]