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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]

In this study, both quantitative and qualitative approach for estimating the aging behaviors of gray cast iron (GCI) alloy at different times and temperatures was adopted. The data were obtained from laboratory experimental tests conducted to determine the mechanical properties of the produced GCI alloys. Model was developed using linear differential equation to ascertain the degree of certainty of the effect of the variables (time and temperature) on the properties such as hardness, impact toughness, ultimate tensile strength (UTS), and wear resistance (WR) of the GCI alloys. The results of the model validation showed that there is positive association between experimental data and model predicted data, the standard deviation values are much closer to the mean, a positive or direct linear correlation exists between the two data for all the alloys, there is high degree of direct correlation between experimental and model predicted data, the standard errors were less than 10%, and the confidence intervals at 95% confidence level are within the acceptable tolerance. The model therefore was accepted. From the model, a software package was developed using VISUAL BASIC system. It is users friendly and runs on the computers with VISUAL BASIC, MATLAB TOOL, and EXCEL PACKAGES of at least 64-MB RAM and 3.0-GB free hard disk. It can also run on higher-grade computers such as Pentium-3 and Pentium-4. [ABSTRACT FROM AUTHOR]

In this work, the repair volume of AISI H13 tool steel samples with hemisphere-shaped defects was reconstructed through reverse engineering and the samples were repaired by laser-aided direct metal deposition (DMD) using Co-based alloys powder as the filler material. Microstructure characterization and elemental distribution of deposits were analyzed using optical microscope (OM), scanning electron microscope (SEM), and energy dispersive spectrometry (EDS). Mechanical properties of repaired samples were evaluated via tensile test and microhardness measurement. The experiment showed that a gap between deposits and substrate exists if only employing the tool path generated from the reconstructed repair volume but the gap can be removed by depositing an extra layer covering that region. Microstructure and tensile test confirmed strong metallurgical bond in the interface. Defect-free columnar structure dominated the deposits near the interface while other regions of deposits consisted of dendrite structure with interdendritic eutectics. The tensile test showed that the repaired samples have a higher ultimate tensile strength (UTS) and lower ductility compared with those of base metal. Fractography from tensile test showed repaired samples fractured brittlely at the deposits section with cracking propagating along the grain boundaries. The hardness measurement showed that the deposited layers have a much higher hardness in comparison to the substrate. [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]

In this work, three cavity structures of radialbackward extrusion (RBE) have been employed to produce Al-Cu-Mg-Zn alloy cup-shaped part. The effects of the cavity structure on the average effective strain, forming load, and forming damage of cup-shaped part produced by RBE were investigated by finite element simulations, and then the influences of frictional coefficient and ram speed on the forming damage were also studied. Comparisons of mechanical properties and microstructure between cup-shaped part produced by RBE and by traditional backward extrusion (TBE) were conducted by experimental works. The finite element simulation results show that the minimum average effective strain and maximum forming damage were acquired in RBE with type-A cavity (RBE-A); the maximumaverage effective strain and minimum forming damage were obtained in RBE with type-B cavity (RBE-B), and the forming damage and average effective strain were moderate if RBE with type-C cavity (RBE-C) has been used. For RBE-A, RBE-B, and RBE-C, the forming damage decreases as ram speed increases or frictional coefficient decreases. With the identical frictional coefficient and ram speed, the forming load increases in an order from type-A cavity, type-C cavity, and type-B cavity. The average effective strain in RBE-C is about 1.9 times of that in TBE. The uniform degree of deformation in RBE-C is far better than that in TBE. The experimental results show that after RBE-C, ultimate tensile strength and yield strength of tube length of formed part are significantly larger than that after TBE, and ultimate tensile strengths and elongation of tube length are around 349 MPa and 22%, respectively. Better refinement of grain and more uniform distribution of strengthening phase can be achieved by RBE-C than by TBE. [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]

GPa-grade steels which possess the ultimate tensile strength over 1000 MPa and higher elongation have been thoroughly researched to replace conventional high-strength steels in automobile industry to enhance fuel efficiency without sacrificing crashworthiness. However, high strength of GPa-grade steel does not only induce punching pin buckling due to high contact pressure, but also abrasive wear on the mold surface due to the unstable contact that results from the large amount of springback, which tend to impede widespread usage of GPa-grade steels. In this research, design criteria for an optimal aspect ratio of the punching pin preventing buckling failure has been proposed by linking with experimental and numerical analyses, which is validated with the analytic solutions. Furthermore, in order to prevent stripping failure, it is highly recommended that one of the main factors, a blank holder force (BHF), over 1.5 MPa has to be maintained during the withdrawal process to minimize the effect of springback in stamped panels applying GPa-grade steel, which is able to extend the tool life of the side punching pin about 100,000 cycles. [ABSTRACT FROM AUTHOR]

Thick plates of 5083 aluminum alloy are welded with GMAW and GMAW-TW processes; the influence of weld pool convection on porosity formation, microstructure, and mechanical property of the welding joints is investigated. The results showed that due to the appearance of outward flow and 'push-pull' patterns, and intense mixing and stirring effects in GMAW-TW process, a sound weld seam with less porosity can be obtained. The less probability of bubble formation, the shorter escaping distance of the bubble, the easy splitting of bubble, the higher bubble escape velocity, and lower solidification rate are responsible for porosity suppression. Even though the grain size in GMAW-TW process is larger than that in GMAW process, the ultimate tensile strength of the joints is larger, which is caused by less porosity formation, larger number, and uniform distribution of second-phase particles in the welds. Compared with GMAW process, the GMAW-TW process possesses the advantages of higher efficiency, less weld defects, and higher mechanical property in the welding of 5083 aluminum alloy thick plates. [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]

In this work, solid silicon (Si) microneedles with a higher aspect ratio and sharper tips are fabricated. Tetramethylammonium Hydroxide (TMAH) etching factors have been optimized and used to fabricate long and tapered microneedles. The needles thus fabricated are found to be suitable for transdermal drug delivery applications. The optimized etching factors include varying the concentration of TMAH, etching time, etching rates, temperature, and window size of optical mask. It is found that by increasing the window size, the etch rates in both vertical and lateral directions increase extensively. However, on increasing the temperature beyond 90 °C, etching becomes rapid and uncontrollable. In order to obtain microneedles with high aspect ratio, sample placement in the glass boat of TMAH setup and TMAH concentration should be manipulated to attain a higher etch rate in vertical direction compared to the lateral one. Solid silicon microneedles with an average height of 158 μm, base width of 110.5 μm, aspect ratio of 1.43, tip angle of 19.4° and tip diameter of 0.40 μm are successfully fabricated. A microhardness value of 44.4 (HRC) was obtained for the fabricated Si microneedles. This is 52.2 times higher than the skin Ultimate Tensile Strength (UTS), which makes insertion of microneedles through the skin safer and easier without any breakage. [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]

Single pass autogenous butt welds, without detectable volumetric defects, were manufactured by electron beam welding 90-mm-thick UNS S41500-a low carbon 13% Cr-4% Ni martensitic stainless steel typically used for hydroelectric turbine applications. The mechanical properties of the joints were evaluated in the as-welded condition by tensile testing, Charpy V-notch testing, and bend testing. Specifically, static tensile loading was conducted on samples extracted transverse and longitudinal to the weld seam. To determine the impact toughness of the electron beam welded joints, the Charpy tests were conducted on samples with V-notch roots located in the fusion and heat-affected zones at −18 °C. The yield strength, ultimate tensile strength, elongation and toughness of the electron beam welds were found to more than adequately meet the minimum acceptance criteria specified in ASME section VIII and IX. Also, the formability of the welds, examined by bend testing, displayed no discontinuities on the tension side of the bent joints. These promising mechanical properties determined for the as-welded UNS S41500 stainless steel offer considerable prospects for industrializing the electron beam welding process. [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]

In this research, dissimilar butt joining of an Al-Mg alloy (AA5083) to austenitic stainless steel (A316L) by using friction-stir welding (FSW) process was examined. FSW parameters and joint design were optimized, owning to achieve the best joint strength. The processed FSWs at the optimized traverse speeds of 16, 20, and 25 mm/min with the sound surface appearance were considered for further cross-sectional investigations, microstructural characterizations, and mechanical testings. In situ reactions at the interface of Al-Mg alloy and stainless steel during FSW processes were studied by using field emission-scanning electron microscopy (FE-SEM) and line-scan energy-dispersive X-ray spectroscopy (EDS) analysis. As expected from the monitored thermal histories during FSW joining, the features indicating the formation of tunneling like defects were observed at low heat inputs (low w/ v ratios). Moreover, some discontinuous thin intermetallic layers (with the thickness of ∼0.5 μm) were formed at the joint interface at the expressed processing conditions. Mechanical performances of the prepared dissimilar joints were assessed during transverse tensile loading and Vickers indentation micro-hardness testing. The joint strength ratio to the ultimate tensile strength (UTS) of the weakest base metal (BM) was improved up to ∼93 %, as all of the dissimilar FSWs failed from the Al-Mg base alloy, with a Vickers hardness enhancement of ∼460 % at the interface. [ABSTRACT FROM AUTHOR]

For the joints of bobbin tool friction stir welding (BT-FSW), welding factors such as welding speed, tool rotation speed, and shoulder pinching gap have significant effects on the ultimate tensile strength (UTS) and tensile elongation (TE). This work developed empirical models to describe the relationships between the welding factors and the tensile properties of bobbin tool friction stir-welded 2219-T87 aluminum alloy. Based on the models, the factor effects can be analyzed quantitatively and graphically, and the UTS and TE of the joints can be predicted and optimized effectively. Firstly, experiments were carried out according to a three-factor and five-level central composite design (CCD). Secondly, empirical models were developed by fitting experimental data points. Adequacies of the models were checked by the analysis of variance (ANOVA). Thirdly, the analysis and optimization processes were conducted. Based on the expressions and plots of the developed models, the individual and interactive effects of the welding factors were investigated. By the multiple-desirability function and three-dimensional response surface methodology (RSM), the optimum welding factors were calculated from the models. The validation trial has been carried out, and the result shows that the models are adequate for predicting and optimizing the BT-FSW factor effects. [ABSTRACT FROM AUTHOR]

In the present work, the AA5052 aluminum sheets were joined by friction stir welding (FSW) technique. In order to refine the microstructure of stir zone (SZ) and to prevent the grain growth of heat-affected zone (HAZ), the SiC nano-particles were added to the weld nugget. To obtain the optimum condition for FSW, three rotational speeds (800, 1000, and 1250 rpm) and three traveling speeds (30, 50, and 80 mm/min) were applied. Microstructural evolutions were characterized using optical and scanning electron microscopes. Besides, the mechanical properties (tensile strength, hardness, and wear test) of weldment were also studied. The results showed that adding the SiC nano-particles led to the significant grain refining of the welds. However, the improper SiC powder distribution during one pass of FSW resulted in the premature fracture of workpiece. The specimens joined at the rotational speed of 1000 rpm and welding speeds of 50 and 80 mm/min exhibited the highest ultimate tensile strength. [ABSTRACT FROM AUTHOR]

Innovative welding techniques allow for the fabrication of light, high-specific-strength, and fuel-saving Al and Mg alloys for use in transportation industries. Furthermore, these techniques have minimal detrimental impact on the environment. However, the poor mechanical properties of joints resulting from the formation of brittle AlMg intermetallic compounds are key barriers to joining Al and Mg alloys. To date, a proper solution to this problem has not yet been provided. The aim of this research was to investigate the mechanical and metallurgical properties of the joint between AZ31B and A7075-T651 alloys welded by a new technique called gas metal arc plug welding method. ER5356 aluminum wire was used as a filler. The yield and ultimate tensile strengths as well as impact toughness of the joints were measured. The fracture surface was investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The maximum ultimate tensile strength and impact toughness of the joints were 89 and 84 % of those of the AZ31B parent alloy, respectively. Generally, the joints failed in the ER5356 nugget, whereas some failed in the AZ31B alloy. No fracture was observed in the A7075-T65 alloy. Brittle fracture mechanism was observed for all the joints. In conclusion, the proposed welding technique can allow for better mechanical properties of joints for dissimilar welding of aluminum and magnesium alloys. [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]

Five tools with different pin-tip profiles like thread taper, triangular, square, three grooves, and conical platform were designed to friction stir weld 20-mm-thick AA7075 alloy plates. The effects of pin-tip profiles on thermal cycles, material flow, and mechanical properties of the joints were studied. The results show that the temperature greatly decreases from the top to the bottom of the weld, and higher peak temperatures along the thickness are obtained using three grooves tool. Due to poor plastic flow reflected by local transfer behavior of material, thread taper and conical platform tools yield macro cross-sectional level pore defect on advancing side in nugget zone. However, triangular, square, and three grooves tools produce defect-free joints due to improving plastic flow resulted from stronger pulsating action and stirring power, leading to higher transfer displacements of local material. The tensile test results show that the joints fabricated by three grooves tool have better mechanical properties including strength and ductility owing to better material flow. A higher ultimate tensile strength of 391 ± 10 MPa, yield strength of 310 ± 12 MPa, and elongation of 8.3 % are obtained, respectively. This can be attributed to finer grains, greater natural aging response and optimum hardness. [ABSTRACT FROM AUTHOR]

Electric pulse–assisted machining (EPAM) can improve the quality of the machined surface, lower the machining stress on the material, and increase the material's machinability. It offers a useful machining technique for working hard and difficult-to-machine metals with little plasticity. To account for this, this paper reviews experiments of EPAM using the electroplasticity effects (EPE) of metals and describes the use of electroplasticity in terms of plastic forming machining and cutting machining, and it also depicts the processes and benefits of EPAM. The experimental results show that the partial stress reduction during EPAM is up to 70%, the roughness is decreased by 40%, the work-hardening is reduced by 44%, and the material's machinability is partially improved. Various hypotheses have been pioneered by academics regarding the electroplasticity effect's mechanism, and they have all undergone experimental testing. Most academics today think that there are various mechanisms involved in electroplasticity, and that certain metals have various mechanistic effects. The paper gives theoretical suggestions for the use and further development of electroplasticity by summarizing the current processes of electroplasticity in terms of thermal and athermal effects. The thermal effect is the Joule heating effect. Other athermal effects include the electron wind effect, skin effect, pinch effect, magnetostrictive effect, de-pinning effect, and vibration effect. A summary diagram of the application and mechanism effects of EPE in processing is also included in the script. Finally, the article summarizes EPE, provides a constructive outlook on the future development of EPAM, and reveals the current problems. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) technologies have transformed manufacturing, by providing greater control over material deposition and consumption. Thanks to greater customization and their high strength-to-mass ratio, the AM of composite materials has significantly grown over the past few years. The main focus in this research area is improving printing precision and higher production rates. However, there is a lack of thorough analysis on the energy consumption of fused filament fabrication (FFF) machines for composite manufacturing, especially when associated with mechanical and economic aspects. We designed an experimental method, based on flow analysis for measuring the impact of temperature parameters on total cost, energy consumption, and tensile resistance of composite parts made by FFF. The user should be able to improve FFF efficiency regarding economic, energy, and technical aspects and obtain recommendations for setting up and using the machine. This study confirms that combining traditional economic and technical indicators (total cost and tensile resistance) with emerging energy indicators (specific energy consumption) can be successfully applied to additive manufacturing to provide an overview of printing parameters impact. Results are yielding information to support optimization investigations depending on the need and goal. For example, two tested parameter combinations that offer similar tensile properties (4% reduction in tensile resistance compared to the best combination) show a 20% difference with lower energy consumption. [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]

This paper describes the joint properties of the friction welded joint between 6061 (AA6061) Al alloy pipe and Al-Si12CuNi (AC8A) Al cast alloy pipe. When joints were made with a friction pressure of 25 MPa, a friction speed of 27.5 rps, and a forge pressure of 30 MPa, the joint strength increased with increasing friction time, and it was approximately 40 % of the ultimate tensile strength of the AC8A base metal at a friction time of 2.0 s. However, all joints fractured at the weld interface between the AA6061 side and the AC8A side, which had an AC8A adhering to the weld interface on the AA6061 side (mixed-mode fracture). When joints were made at a friction time of 0.3 s with the same friction pressure and friction speed, the joint strength increased with increasing forge pressure, and it was approximately 60 % of the AC8A base metal at a forge pressure of 175 MPa. Many joints had the fracture at the AC8A side although one of the joints had at the mixed-mode fracture. On the other hand, when joints were made at friction times of 0.7 and 2.0 s, the joint strength was approximately 60 % of the AC8A base metal at a forge pressure of 75 MPa. Those joints fractured on the AC8A side, because the adjacent region of the weld interface was softened. In addition, the flash of the joint with a friction time of 0.7 s was fewer than that of 2.0 s. To obtain the joint with the fracture from the AC8A side, the joint should be made with the opportune friction time such as 0.7 s and the opportune forge pressure such as 75 MPa because this joint had no cracks at the weld interface. [ABSTRACT FROM AUTHOR]

The requirement of weight reduction, high thermal conductivity and strength at low temperatures and high corrosion resistance has identified the use of Al alloys together with steel in various fields. The use of Al alloys together with steel warrants efficient joining of Al alloys with steels. Friction stir welding (FSW) is a potential candidate for the joining of difficult-to-weld similar and dissimilar materials due to its inherent advantages as a solid state joining process. In order to speed up the research activities that lead to industrial level implementation of FSW of dissimilar Al alloys and steels, modelling and simulation can play a vital role. In this work, a central composite-response surface method (RSM) model is developed to predict the ultimate tensile strength (UTS) of friction stir-welded dissimilar Al alloy AA5052 H32 and HSLA steel IRS M-42-97. The adequacy of the model is verified by the analysis of variance (ANOVA) and computed values of the actual and adjusted R values. The model is validated by the results of experimental trials at parameter combination other than that experimented as per the DOE matrix and found in agreement with an average error of −0.34 %. From the analysis of the developed model, it is observed that the UTS of the joint is very sensitive to the primary FSW parameters, and, as such, the range of primary FSW parameters that could produce significant joint strength is very narrow. Also, it is observed that the tool rotational speed, welding speed and axial force have a significant interaction effect on the UTS of the joint. The analysis of the model and discussion on the effect of FSW parameters on the tensile strength of the joint are supported by the results of scanning electron microscopy and EDS analysis at the joint interface of selected joints. [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]

In the present study, a number of joints were fabricated successfully on DH36 marine steel sheet in underwater wet based on friction taper plug welding (FTPW). The influences of the plug and hole geometry parameters combination on the quality of welded joint forming were first investigated. It was found that tapered holes and plugs were the preferred choice and a suitable cone angle range was obtained. Using the preferred hole and plug designed further expand the range of welding parameters to explore process parameters influence on the welding quality. Bonding mechanism and microstructural evolution to FTP welds were investigated with multiple observations. Mechanical properties of the obtained joints were also evaluated with tensile and Charpy impact tests by reference to AWS D3.6 Underwater Welding Code. The best result is found as the joint welded with 7500 rpm and 40 kN which has 535.6 MPa ultimate tensile strength, 22.5 % elongation, and 42.5 J impact energy at bonding line. [ABSTRACT FROM AUTHOR]

The effect of process parameters on vertical forces and temperatures developed during friction stir welding of AZ31 magnesium alloy sheets was widely investigated. To this end, friction stir welding (FSW) experiments were carried out with constant values of the rotational and welding speeds in the ranges from 1200 to 2500 rpm and from 30 to 100 mm/min, respectively. The influence of the time between the end of the sinking stage and the beginning of the welding one was also studied using dwelling time values ranging from 0 to 120 s. Vertical forces occurring during all stages of FSW were measured using a low-cost dynamometer developed by authors. Furthermore, temperatures in different positions of the welding line were monitored by means of K-type thermocouples. It was shown that during the dwelling stage, the vertical force decreases until a steady-state regime is reached. However, the dwelling time does not significantly affect the force value in the welding stage. The vertical force versus time curve promptly reaches a steady state during the welding stage. The force value rises with increasing welding speed and decreasing rotational speed; such effect is consistent with the one showed by rotational and welding speeds on temperature measured in different positions during FSW. Finally, forces and temperatures have been related to the mechanical properties of the joints. It was shown that both the ultimate tensile strength and ultimate elongation exhibit the highest values under the process parameters leading to the lowest vertical force and highest welding temperature. [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]

The production of refined grain materials by equal channel angular extrusion (ECAE) method has been the subject of numerous research programs over the past decades. In this study, the mechanical properties of commercially Al-6063 alloy deformed through ECAE process are investigated. The extrusion is performed up to six passes at a constant speed of 30 mm/min and a temperature of 200 °C. The grain size of the material reduced from 45to 2.8 μm after six passes. The extruded specimens were tested under quasi-static, medium, and high strain rate loadings using various testing machines. The results indicated that the tensile yield stress (YS) and the ultimate tensile strength (UTS) of the extruded specimens increased significantly after five passes of the ECAE process. The major improvement occurred after the first pass. For the subsequent passes, the properties kept improving but at lower rates. It was also shown that the tensile properties of the processed specimens are not influenced by the strain rate. [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]

Nanoceramic-reinforced aluminum composites have been utilized in most engineering applications such as the automotive and aerospace components due to their mechanical strength efficiency, and tribological performances. In this research, efforts were made to develop AA8011 composite with varying weight fraction of nano-Si3N4 up to 20% in a step of 5 through a two-step stir casting process. Scanning electron and the optical microscope were employed to investigate the microstructural evolution and modification of the developed composite, which reveals even dispersion of Si3N4 particulates. The X-ray diffraction analysis was conducted to check the phases present, and the broad peak shows mainly the presence of Si3N4. Likewise, the mechanical properties, viz, ultimate tensile strength, yield strength propagation, and hardness, were examined to determine the strengthening mechanism of the developed composite. The results show that the reinforced composite possesses better mechanical properties compared with the unreinforced AA8011 and the composite with 20% Si3N4 inclusion had the best properties. Moreover, the wear behavior and the friction coefficient of the developed composite results depicted an enhanced wear resistance and decrease in the coefficient of friction by increasing the Si3N4 particulate, though the wear rate increases with an increase in the applied load from 20 to 40 N. [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]

Taguchi's approach to design of experiment was applied to determine the effect of some process parameters on the mechanical properties and microstructures of castings obtained by evaporative pattern casting process. Four process parameters with three levels were selected and used with Taguchi's method to give nine experimental runs. Casting design system was employed to determine the gating parameters for each of the test castings in the study. The pattern material was polystyrene of density 2 g/cm. The mechanical property tested where the ultimate tensile strength (UTS), percentage elongation and hardness value. It was observed that castings produced at pouring temperature of 650 °C had fine grains and the highest values of UTS and hardness values. There was a downward trend of these values as the pouring temperature increased from 650 to 700 °C and then to 750 °C. It was established that producing the Al alloy castings at pouring temperature close to 650 °C results in good mechanical properties and microstructures. [ABSTRACT FROM AUTHOR]

In this study, a thermal model was developed and applied to simulate the friction stir welding of pure copper plates with the thickness of 2 mm. The different traverse speeds of 100, 200, 300, and 400 mm min and rotational speeds of 400, 700, 900 rev min were considered as welding parameters. Microstructural characterization, hardness measurement, tensile test, and fractography were conducted experimentally. The comparison between the numerical and experimental results showed that the developed model was practically accurate. In addition, the results confirmed that the peak temperature was the dominant factor controlling the grain size and mechanical properties, where the fine grains could be achieved at low rotational speed as well as high traverse speed. Consequently, lower peak temperature leads to the high ultimate tensile strength and hardness and the low elongation values. [ABSTRACT FROM AUTHOR]

Parts with aluminum and zinc alloys mostly are produced by casting techniques. However, low production cost and lack of need for machining makes it necessary to produce ZAMAK alloys using a powder metallurgy method. Also, the production of ZAMAK alloys using a powder metallurgy method can be considered as a modern technique competitive to the gravity and die-casting techniques, due to its capability to produce parts with near-net shape and dimensions, self-lubrication, and sound-damping characteristics caused by the residual porosity deliberating left in these parts and the economics of the overall process. In this way, we study the production of ZAMAK 2 that has the maximum ultimate tensile strength among the ZAMAK alloys using a powder metallurgy technique. Mechanical methods were used to produce the powder, and the high-grade zinc powder was produced in three meshes. The resulting powder was mixed with powdered aluminum, copper, and magnesium. The final powder is ready to press now. The plots were pressed at three pressure rates: 500, 400, and 350 MPa. The components at temperatures 375, 260, and 160 °C were sintered that led to the production of 27 samples for investigation. The density, tensile strength, and hardness of generated samples were studied and compared to each other. The conditions that lead to produce the maximum hardness, maximum tensile strength, and maximum density were investigated. [ABSTRACT FROM AUTHOR]

In this paper, effect of pin position (relative to tool shoulder position) on welded joint in friction stir welding (FSW) of aluminum 5083-O was investigated. FSW is a new solid-state welding process used to join metals and alloys (especially unweldable aluminums). To do this study, a FSW process was prepared by designing and fabricating tool and workpiece fixture and installing them on a milling machine. Then, some experiments were performed using the tool with a pin coaxial with the axis of tool shoulder. Hence, the tool enters edges of joint location and moves along joint line. Achieved results showed heat generation, severe plastic deformation, and material displacement in joint location which led to completeness of joint's edges. It was also found that the tool temperature for tools with half pin and arched pin had a significant increase with the increase of rotational speed. Tools with more ability of mixing materials and forging of transferred material from the front of the pin to its back showed more ultimate tensile strength. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) has gained great importance in the recent development to produce metallic structural elements for civil engineering applications. However, research effort has been focused mainly on powder-based processes, while there is still limited knowledge concerning the structural response of wire-and-arc additive manufactured (WAAM) metallic elements, and very few experimental data concerning their mechanical properties. This paper presents the first results of a wide experimental campaign aimed at assessing the mechanical properties of WAAM plates produced using a commercial ER308LSi stainless steel welding wire. The aim is to evaluate the effect of the orientation in the tensile behavior of planar elements considering specimens extracted along three different directions with respect to the deposition layer: transversal direction (T), longitudinal direction (L), and diagonal direction (D). Compositional, microstructural, and fractographic analyses were carried out to relate the specific microstructural features induced by WAAM to the mechanical properties. The results show that the chemical composition of the plates meets the requirements of UNS-S-30403 for an AISI 304L austenitic stainless steel. The as-built samples were substantially defect-free and characterized by a very fine microstructure of γ and δ phases The fineness of the microstructure and the negligible defect content led to values of tensile strength and elongation to failure in line with the traditionally manufactured stainless steel elements. Anisotropy in the tensile properties between T, L, and D specimens was observed, and the highest elastic and plastic properties were measured in D specimens. This result is related to the crystallographic and mechanical fibering induced by the additive process, that led also, in case of D samples, to the highest density of cell boundaries, obstacles to the dislocation slip, located at 45° with respect to the loading direction, where plastic deformation preferentially occurs. [ABSTRACT FROM AUTHOR]

This study focuses on the impact of different fabrication parameters (build orientation, layer thickness and post-curing time) on the mechanical properties of parts fabricated through projection stereolithography technology. A Titan 2 HR printer (Kudo3D Inc.©) was used to print the specimens. Three different resins have been investigated. Specimens have been organised in 7 families for each material. Besides the different chemical compositions of the resins, the results globally show that the most influential factor on the mechanical properties (ultimate tensile strength, Young's modulus, elongation at break) is the build orientation. Contrarily, the effect of the post-curing time has proved to be highly dependent on the chemical composition of polymers, playing a significant role only for resins that do not complete the polymerisation process during printing and therefore require a subsequent treatment time. Layer thickness in this application has shown a relevant influence on the mechanical characteristics of the studied resins. [ABSTRACT FROM AUTHOR]

Abstract   : The fact that the weld geometry is vital in the cooling rate and determining the weld metal quality is obvious to all. So, the Taguchi technique was used to determine the process parameters of gas metal arc welding to access optimal weld bead geometry. In addition, this study investigated the effect of siliconized Zn-graphene oxide complex nanoparticles as one of the input parameters on the weld bead geometry, including the penetration depth, bead height, and bead width of the weld. Hence, the S/N and ANOVA statistical analyses were done to establish the relationship between the gas metal arc welding process's input parameters and output variables to achieve the weld bead with the highest penetration depth and the lowest bead height and width. The results showed that in the L00 sample compared to the L0 sample (sample without nanoparticles), in addition to having a very high penetration depth, the ultimate tensile strength, and yield strength have increased by 58.84% and 28.24%, respectively. [ABSTRACT FROM AUTHOR]

The innovative hot stamping press of quenchable steel mainly includes two stages: hot forming of blank at elevated temperature and quenching of hot stamped part in closed water-cooled tools. Crucial stage in hot stamping process is quenching of hot formed part in water-cooled tool to achieve final high ultimate tensile strength. In quenching stage, cooling rate of hot stamped part has a significant effect on final mechanical properties of hot stamped part. Hence, in this paper, a new method is proposed to optimize cooling system to improve effectiveness of quenching and thus final mechanical properties of hot stamped part. In this method, cooling channel is introduced in tools, and hot stamping experiments are combined with corresponding finite element numerical simulations to optimize cooling system. According to cooling system optimization, two different sets of tools used to manufacture square-box-shaped part and B pillar of automobile are manufactured using drilling method and pre-embedding method, respectively. Hot stamping experiments and corresponding simulations are performed to verify the effectiveness of optimized cooling system. [ABSTRACT FROM AUTHOR]

Laser transformation hardening (LTH) is an innovative and advanced laser surface modification technique as compared to conventional transformation hardening processes and has been employed in aerospace, marine, chemical applications, heat exchangers, cryogenic vessels, components for chemical processing and desalination equipment, condenser tubing, airframe skin, and nonstructural components which introduces the advantageous residual stresses into the surface, improving the mechanical properties like wear, resistance to corrosion, tensile strength, and fatigue strength. In the present study, LTH of commercially pure titanium, nearer to ASTM grade 3 of chemical composition was investigated using continuous wave 2 kW, Nd: YAG laser. The effect of laser process variables such as laser power, scanning speed, and focused position was investigated using response surface methodology (RSM) and artificial neural network (ANN) keeping argon gas flow rate of 10 lpm as fixed input parameter. This paper describes the comparison of the heat input (HI) and ultimate tensile strength ( σ) (simply called as tensile strength) predictive models based on ANN and RSM. The paper also presents the effect of laser process variables on the HI and ultimate σ. The research work also emphasizes on the effect of HI on σ. The experiments were conducted based on a three-factor, three-level Box-Behnken surface statistical design. Quadratic polynomial equations were developed for proper process parametric study for its optimal performance characteristics. The experimental results under optimum conditions were compared with the simulated values obtained from the RSM and ANN model. Adequacy of the developed models was tested by analysis of variance technique. A multilayer feed-forward neural network with a Levenberg-Marquardt back-propagation algorithm was adopted to develop the relationships between the laser hardening process parameters, HI, and ultimate σ. The performance of the developed ANN models were compared with the second-order RSM mathematical models of HI and σ. There was good agreement between the experimental and simulated values of RSM and ANN. The comparison clearly indicates that the ANN models provide more accurate prediction compared to the RSM models. It has been found that there is a trend of increased tensile strength with the decrease of hardening heat input and a trend of increased tensile strength with the increase of hardening cooling rate. As heat input decreases, there will be a faster cooling rate. Considering the effect of HI on ultimate σ, it was found that the lower the heat input, the faster cooling rate. The details of experimentation, model development, testing, validation of models, effect of laser process variables on heat input and ultimate σ, effect of HI on σ, and performance comparison of RSM and ANN models are presented in the paper. The results of Box-Behnken design of RSM and ANN models also indicate that the proposed models predict the responses adequately within the limits of input parameters being used. It is suggested that regression equations can be used to find optimum conditions for HI and σ of laser-hardened commercially pure titanium material. [ABSTRACT FROM AUTHOR]

This paper explores common process variations encountered in friction stir welding (FSW) and the limits to which acceptable joint strength is maintained while welding with a robotic FSW system. Part fit-up and mating variations are common in manufacturing, yet the limits to which a friction stir welding process can weld without major process adjustment are unclear. The effects on joint strength and mechanical properties of several of the most common mating variations (i.e., faying surface gap, misalignment, mismatch, etc.) are experimentally determined as individual effects as well as among common welding parameters. Experimental results on 5-mm-thick aluminum alloy 5083-H111 show that ultimate tensile strength, yield strength, and elongation begin to decrease from nominal weld conditions when either the tool offset distance from weld centerline or gap in abutted plates exceeds 25% of the average pin diameter (6 mm). In addition, vertical plate mismatch and lack of penetration can be tolerated up to 2.5% and 10%, respectively, before adverse effects on mechanical properties are observed. The work also indicates that of all the mating variations tested in this study, tool misalignment, followed by travel angle, has the most significant effect on the measured joint strength. Process stability testing has shown that the FSW process is able to endure part fit-up and mating variations within a defined tolerance, giving the practitioner an awareness of how well stock workpiece tolerances must be controlled before joint strength is adversely effected. [ABSTRACT FROM AUTHOR]

The potential machinability for Alloy 718 (Inconel 718) is examined in terms of five material characteristics considered to play a key role in the machinability: ductility (elongation to fracture), strain hardening (ultimate tensile strength over yield strength), thermal conductivity, yield strength and abrasiveness (amount of carbides). The material characteristics are simulated with the software JMatPro from Sente software. The effects of composition, grain size, hardness (size of the precipitated intermetallic particles for given volume fraction), heat treatment, temperature and strain rate have been modelled and statistically evaluated. Combining thermodynamics-based modelling (JMatPro), design of experiments and statistical analysis (Minitab), and machinability polar diagram, a concept on methodology to assess variations in material specifications and to optimise these specifications with respect to potential machinability has been developed. The mechanical properties, predicted from the meta-modelling are found to be affected by the same parameters: hardness (intermetallic particles characteristics), grain size, amount of aluminium, strain rate and temperature. The abrasiveness should only be affected by the amount of carbon. Simulated material characteristics for two different types of turbine discs were compared with measured tool wear from production environment machining experiments. Variations in material characteristics between the discs were small as well as the critical tool wear, revealing a robust metal cutting process. [ABSTRACT FROM AUTHOR]

The present work focused on the densification behaviour and heat treatment effect on the mechanical properties of spark plasma sintered Ni–Fe–Al–Cr alloys. Five initial alloys were prepared by mixing of elemental compositions of each alloy followed by sintering. The five alloys, Ni–30Fe–20Cr, Ni–30Fe–15Cr–5Al, Ni–30Fe–10Cr–10Al, Ni–30Fe–5Cr–15Al, and Ni–30Fe–20Al, were sintered at sintering temperature of 950 °C, pressure of 50 MPa, heating rate of 150 °C/min, and at a holding time of 10 min and heat-treated. Microstructure and mechanical properties of the sintered alloys were investigated prior to and after heat treatment by scanning electron microscopy (SEM) and a Future-tech Vickers microhardness tester respectively. Results showed that the relative density of the alloys increases as the aluminium content increases. The microhardness increases at 800 °C for 2 h ageing time and decreases after prolonged ageing. Therefore, optimum strengthening of sintered nickel alloys can be obtainable within short duration of ageing as prolonged results in adverse hardness values. [ABSTRACT FROM AUTHOR]

In this study, the effect of friction-stir welding (FSW) parameters such as spindle rotational speed, traverse speed, and stirrer geometry on mechanical properties of AA 1050/AA 5083 alloy couples were experimentally investigated. Ultimate tensile strength (UTS) and hardness of welded joints were determined for this purpose. The full-factorial experimental design was conducted to obtain the response measurements. Analysis of variance (ANOVA) and main effect plot were used to determine the significant parameters and set the optimal level for each parameter. A linear regression equation was derived to predict each output characteristic. The experimental and predicted values were in a good agreement with a R2 of 0.82 and 0.93 for UTS and hardness, respectively. [ABSTRACT FROM AUTHOR]