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Heavy reduction (HR), during which a large reduction deformation is implemented around the strand solidification end during continuous casting, is a novel technology that could effectively improve the internal quality of large section continuous casting steel. In the present work, a 3 dimensional (3D) thermal-mechanical coupled model with two pairs of rolls was developed. By setting different rotation speed of the front and the reduction rolls, the effect of differential roll rotation speed on the evolution of internal porosity in continuous casting bloom during HR was investigated. Initial temperature distribution of the 3D thermal-mechanical coupled model was determined by the predicted heat transfer results of a 2 dimensional (2D) heat transfer model. An Arrhenius-type constitutive equation, derived based on the measured true stress-strain curves under different temperatures and strain rates, was adopted in the 3D thermal-mechanical coupled model to describe the metal flow behavior of the casting strand during HR. Accuracy of the 3D thermal-mechanical coupled model was verified by the feedback pressure of the hydraulic cylinders during plant trial of HR. The simulation results indicate that a relatively larger rotation speed of the front rolls (Vf) than that of the reduction rolls (Vr) could effectively suppress the porosity elongation along the casting direction and the bloom width direction, and benefit the decrease of porosity dimension along the bloom thickness direction. As a result, the effect of HR on improving the bloom internal porosity could be effectively promoted. With HR amount of the reduction roll (Rr) decreased or the small reduction amount of the front rolls (rf) increased, the improvement effect of differential roll rotation speed on HR becomes more significant. With roll rotation speed ratio of Rv (Rv = Vf / Vr) increased from 1.0 to 2.0, efficiency of differential roll rotation speed on promoting the process effect of HR continuously decreased.

0.5 mm thick AA7075-T6 ultra-thin sheets were joined successfully by high rotational speed friction stir welding using a pinless tool. Friction stir welding was performed under a high rotational speed of 6000 rpm, and the travel speed ranged from 300 mm/min to 1200 mm/min. Zero thickness reduction and delamination phenomenon were observed in the nugget zone when the travel speed was 1200 mm/min. In this condition, the dynamic recrystallization occurred in the lower part of the nugget zone is incomplete. The mechanical properties gradually improved with the increasing in the travel speed. All the tensile specimens fractured along the boundary between the thermo-mechanically affected zone and the nugget zone, and the morphology showed a shear fracture mode. The maximum tensile strength of 482 MPa (equivalent to ∼90% of base metal) was obtained at the travel speed of 1200 mm/min, which presented a ductile fracture mode and a large amount of η phase (MgZn2) precipitates and thick tear ridges were detected on the fracture surfaces.

Defect-free Friction stir welded joints between the AZ91 Mg alloy and A383 Al alloy were obtained at a welding speed of 40 mm/min and a rotational speed of 900 rpm. Mg and Al were intermixed and presented intercalated strips microstructure. The second phases Si, Al3Mg2, Al12Mg17 and Mg2Si distributed uniformly in stir zone at a rotational speed of 900 rpm, and there is a narrow intermetallic compounds layer (∼10 μm) at the interface of the two base metals. The tensile strength of the dissimilar AZ91/A383 joint is 93 MPa, which is approximately 45% of the A383 alloy. The sufficient material intermixing and uniform distribution of second phases are helpful to the joint properties.

With the appropriate process parameters, both large and small tools can produce sound joints with tensile strengths (TS) 80% higher than those fabricated with Al base metal. As a large tool moves into the steel, it can peel off and embed steel fragments into the Al matrix, causing critical defects around the embedded fragments. Using small tools and lower rotational speed (RS) will significantly reduce the welding heat, resulting in an unwelded Al/steel interface at the bottom of the weld. Since the tool size and process parameters determine the amount of generated heat, they also determine the thickness of the intermetallic compound (IMC) layer that forms at the Al/steel interface. The welding forces in the weld plane are primarily affected by the tool offset.

Magnetic abrasive finishing (MAF) is one of the most important final machining processes, and the performances of finishing media play an important role in the finishing effects and efficiency. In this study, a new magnetic finishing media with semi-solid state was presented and prepared, and finishing setup for the inner or outer rotary surface was developed. In order to determine the optimum angle between N pole and S pole, simulation was performed using ANSYS Maxwell 14.0. Mathematical modelling of the material removal ratio (MRR) was built as a function of magnetic pressure and velocity based on Archard wear model, and the developed model predicted the MRR as a function of magnetic flux density, mass ratio, rotational speed of magnetic poles, rotational speed of cam, and diameter of abrasive particles and ferromagnetic particles. The material removal coefficient of the predicted model was determined. The model was validated by experiment, and the relative error between the experiment value and the theoretical value was 4.51%. Finishing experiments of main parameters on surface roughness Ra and MRR were examined. Experimental results indicate that the percentage change % ΔRa in surface roughness Ra and the material removal amount increase with the increase of the rotational speed, the mesh number of the abrasive particles, and the mass ratio of base polymer, ferromagnetic phase and abrasive phase. For the 6061 aluminum alloy tube, the maximum improvement in surface roughness Ra is 96.67%, and the maximum MRR is 1.916 mg/s.

Linear lap welds in very thin plates of galvanized steel were produced using tool assisted friction welding, a friction stir welding related technique. The morphological and microstructural analysis of the welds produced with varying tool rotational speed (up to 1400 rpm), tool traverse speed (up to 1200 mm/min) and tool diameter (10–16 mm) revealed the absence of stirred material or important welding defects in most of the joints. For the welds produced with the higher tool traverse and rotational speeds, a strong asymmetry in the weld morphology was also observed. A change in the contact conditions between the tool and the workpiece, from sticking to sliding, is appointed as the main factor responsible for the asymmetry in the weld morphology. The asymmetry in welds morphology has important influence in the failure mode of the welds in lap shear test but no influence on the joint strength. Lap shear strengths similar to base material ultimate tensile strength were measured for most of the welds.

High-quality joints of ultra-high strength C-Si-Mn quenched and tempered martensitic steel were successfully fabricated by double-sided friction stir spot welding (FSSW) with adjustable probes. We found that the mechanical properties of the welded joints increased with the rotation speed, due to the increase of hard phase and strengthened welding interface. In the surroundings of the shoulder/probe interface, a large amount of martensite was formed resulting from the higher austenitizing temperature and the higher cooling rate. In addition, severe material flow vertical to the welding interface and strong relative slip along the interface conspicuously favored the fragmentation and dispersion of the oxides, and the drive force for grain boundary migration introduced by severe material flow further promoted the dispersion of the oxides. Consequently, a high-quality welding interface was fabricated, and a high-strength welded joint with a stable plug failure was obtained. Furthermore, we pointed out that soundly welded high strength interface of ultra-high strength steel can be obtained by higher welding temperature and introducing strong material flow vertical to the interface.

A novel welding tool, characterized by the enlarged pin design was developed to solve the hook feature or insufficient interface deformation for Al/steel friction stir lap welded joints. The welding tool enhanced the interface deformation effect and eliminated hook feature. The thickness of the intermetallic compound (IMC) layer at the interface decreased from 3.3 μm to 0.46 μm, when the welding speed increased from 30 mm/min to 300 mm/min. The laminated structure composed of IMCs and fine steel grains gradually disappeared, with the interface gradually changing from serrated to straight as welding speed increased. The nanohardness value of the microstructure reached 9.4 ± 0.3 GPa at a distance of 10 μm from the interface layer. Due to the larger metallurgical bonding area, the best line load 499.4 N/mm reached 52 % of the 3 mm 6082-T6 alloy, which was obtained at the rotational speed of 1200 r/min and the welding speed of 50 mm/min. Four different interface failure modes were found and established during the shearing process. The strain concentration phenomenon of the successive occurrence, development and transfer of interface failure presented obvious interval characteristics in time and space.

Material mixing and intermetallic compounds (IMCs) are the key factors that affect the mechanical properties of dissimilar metal joints. In this paper, a feasible method of stationary-dynamic shoulder friction stir welding has been developed, which reduces the mixing of materials and inhibit the growth of IMCs during the Al-Cu welding process. The stationary-dynamic shoulder was composed of a stationary shoulder with a larger diameter and a rotational shoulder with a smaller diameter. While the stationary shoulder provided the upsetting force to guarantee the weld formation, the rotational shoulder served for material stirring and heat input. Compared with conventional friction stir welding, the mechanical properties of joints obtained by the new method were significantly improved. The maximum tensile strength was 243 MPa, which was equivalent to 90 % of Cu base metal and 54 % of Al base metal. Furthermore, the evolution of IMCs across the transition layer was analyzed in depth. The results indicated that, with an increase in the rotation speed, the IMCs layer gradually became thicker. However, when the thickness reached a certain level, it promoted the generation of micro-cracks on IMCs and reduced the strength of the joint. According to thermodynamic and kinetic analysis, IMCs were formed with respect to Al2Cu-Al4Cu9 sequence, which was consistent with transmission electron microscopy results.

In order to predict dissimilar materials’ flow behavior during friction stir welding, a morphological simulation of the weldment was performed using Level Set (LS) method. Thermal and computational fluid dynamics (CFD) simulations were conducted to calculate the temperature distribution and material flow velocity during the welding process. Level set model was created to predict the weld morphology based on CFD results. Weld morphologies in different tool rotational speeds, offsets position and height levels of the specimen were simulated. In order to validate the simulations, temperature measurements, optical microscopy (OM) of the weldment and scanning electron microscopy (SEM) of the stirred zone (SZ) were carried out. It was seen that the main cause of defects in the weld zone were steel particles detached in aluminum matrix. The simulation results revealed that increasing rotational speed and offset through the steel side could generate more steel particles. Also, the particles were more in the top height level of the weld section than in the middle and bottom levels.

Effects of varied pin offset on microstructure and mechanical properties of joints were studied during laser-assisted friction stir butt welding between 6061T6 aluminum alloy and commercially pure copper. A suitable laser power was firstly selected by investigating the effect of laser power on the temperature field of the welding. The experiments were conducted with laser power of 700 W, rotational speed of 950 rpm and welding speed of 23.5 mm/min while the pin tool offset distances differed from 0.2 mm to 2.1 mm and the tensile properties were tested respectively. EDS and SEM were adopted to analyze the inter-metallic compounds(IMCs) and microstructure of the joint interface. Inter-metallic compounds of Cu3Al2, CuAl, CuAl2 were observed in stir zone. α-Al/CuAl2 eutecticum and saturated solid solution of Cu in Al were detected in Al matrix. The pin offset distance and the additional heat source of laser beam play significantly important roles in the tensile strengths of the Cu/Al dissimilar joint. Reliable joints with thin IMC layers can be obtained when the laser power is 700 W and the pin offset distance is 1 mm.

Particle image velocimetry (PIV) technique was adopted to understand material flow and measure strain rate around the tool pin during friction stir welding (FSW). The micro-spherical glass tracers in a transparent visco-plastic material, of almost similar densities, were used as experimental materials. The characteristics of material flow, in particular, flow velocity and strain rate were obtained by following the path of the tracer particles. A rotational zone around the tool pin was observed due to large deformation of the material close to the tool pin. The maximum velocity was noted to be 60% (close to the pin surface) of the pin peripheral velocity, and strain-rate was found to be 20 s−1 (0.6 mm away from the pin periphery) at FSW parameters of 170 rpm and 50 mm min−1. The strain rate was found to increase from 8 s−1 to 44 s−1 with increase in rotational speed from 75 rpm to 425 rpm. Predictive correlations were established for variations of velocity and maximum strain-rate as a function of rotational, traverse speeds and distance away from the tool pin surface. Overall, it was established that PIV technique can be utilized for the understanding of material flow and strain-rate behaviour during FSW. Furthermore, this technique enabled in-situ visualization overcoming drawbacks of other techniques reported in the literature.

A model is developed to obtain the friction stir welding (FSW) induced stress in structures, which includes the welding process and the cooling process. The characteristics of the welding stress are presented in the analytical results. A detailed numerical simulation is also performed to verify the effectiveness of the proposed model. Numerical results of the welding stress agree well with the welding stress obtained from the analytical model. Then, the effects of process parameters of FSW on the welding stress are studied by using the analytical model. The process parameters involve the depression depth of the welding tool, the rotational speed, and the advancing speed. The calculated results show that the radial stress in the welded structure decreases with the increase of the depression depth. Larger tensile stress appears beneath the tool shoulder with the increase of the rotational speed. Higher advancing speed introduces lower tensile stress in the welded structure.

Friction Stir Spot Welding (FSSW) of AA5052-H32/HDPE/AA5052-H32 sandwich sheets is performed at six different tool rotational speeds to evaluate the optimum range. The mechanical performance, hook formation, grain size, hardness and temperature distribution are evaluated. Lap shear test, cross tension test, peel test and uni-axial tensile test are conducted. A comparative assessment has been made between the bimetallic and the sandwich sheets after FSSW. The optimum rotational speed for joining the sandwich sheet is 1800 rpm and beyond, where the joint strength and extension to failure are found to be acceptable. In hook formation, two hooks are prominently seen in the sandwich sheets, while it is only one hook in the bimetallic sheets. The hook width increases and the hook height decreases with increase in rotational speed. A mechanism has been proposed to explain such phenomenon. The peak temperature increases with increase in rotational speed and it gets reduced in sandwich sheet as compared to bimetallic. The polymer layer takes a part of the heat flux during stirring to reduce the peak temperature in sandwich system. The bimetallic joints are stronger than sandwich sheet joints showing better joint strength and extension at failure in almost all the tests. Joint hardness distribution supports such performance. Nugget pull-out and partial nugget failure are observed during joint failure of sandwich sheets.

In this work, the thermal behavior of an elastomer flow all along a cylindrical runner placed at the outlet of an extruder is studied. A cylindrical runner thermally regulated and highly instrumented was designed. It is equipped with a new intrusive thermal sensor, developed in the lab and named thermal measurement cell (TMC). This device is used to measure temperature profiles at the inlet and the outlet of the flow. Several experiments are performed with an elastomer by varying the rotation speed of the screw. Experiments first show the influence of viscous dissipation on the thermal behavior of such a highly viscous flow. Then, the results are used to estimate the viscosity by taking into account the temperature profile of the flow. The comparison of the estimated viscosity with the viscosity measured in a capillary rheometer shows the importance to introduce a correction in rheometric characterization and to consider a non-isothermal behavior of the flow. Experimental results are also compared with model predictions. The model is then used to perform a sensitivity analysis. The influence of the correction on the viscosity and the impact of viscous dissipation on the thermal behavior prediction of the elastomer flow are discussed.

The temperature distribution and the residual thermal stresses generated from friction stir welding process were predicted by using finite element analysis (FEA). The predicted temperature was validated experimentally by using infra-red thermal image camera. Different AA5083-O joints were friction stir welded using cylindrical threaded pin profile and tapered smooth one at different rotational and welding speeds. The increase of welding speed values resulted in lower peak temperature during the welding process and the increase of rotational speed caused higher welding peak temperature. Defect-free welds were obtained by using a threaded pin at lower rotational speed (i.e.400 rpm). All the welded joints by the tapered tool pin profile had internal defects at all welding conditions. The maximum tensile strength of 230 MPa was obtained by using the threaded tool at 400 rpm, 50 mm/min while; the minimum one of 85 MPa was obtained by using the tapered tool at 630 rpm, 100 mm/min.

Experimental investigations were carried out using a numerically controlled milling machine to weld ultra-thin copper foils (20 μm and 50 μm thickness).Welds were analyzed by optical microscopy, scanning electron microscopy (EDS), tensile shear tests and micro-hardness. The ultimate maximum shear-load could be achieved up to 56N with the rotation speed of 800 rpm and the traveling speed of 25 mm/min, which should be attributed to optimum heat and pressure. The interface bonding mechanism was also expounded and three main influence factors were analyzed in detail respectively.

Friction stir lap welds in thin sheets of AA6082-T6 aluminium alloy were performed at a constant tool rotation speed (600 rpm) and traverse speeds ranging from 250 to 1600 mm/min, using a non-threaded conical pin tool. As-welded and heat-treated samples were subject to tensile-shear and transverse-tensile testing in order to determine the joints strength and the weld materials mechanical properties, respectively. The presence of weld defects, as well as its location and severity, were evaluated by analysing the strain distribution in the welded samples, which was recorded using digital image correlation (DIC). The as-welded and heat-treated samples were also subject to tensile-shear fatigue testing. It was concluded that increasing the welding speed increases the incidence and severity of lap welding defects. In monotonic loading, the heat-treatment of the welds enabled to increase the yield strength efficiency of the joints free of defects to values close to 100%. In fatigue loading, the strength of the joints was decreased by heat-treating the welds. A FEM analysis was carried out in order to investigate this behaviour. It was concluded that the low strength of the weld material promotes a decrease in stress concentration at the non-welded tip of the joints, contributing to a better fatigue performance of the as-welded joints relative to the heat-treated ones.

A truncated cone-shaped stirring pin with threads was designed to enhance friction stir butt welding (FSBW) quality of AZ31B magnesium alloy and Q235 low carbon steel. The effects of welding speed and rotation speed on the microstructure and properties of joints were studied. Microstructure characteristics and element distribution along the Mg/steel interface were analyzed. The results showed that the truncated cone-shaped stirring pin with threads effectively improves the metal flow behavior, especially the fluidity of steel. A steel-strip was formed at the bottom of the Mg side weld nugget during the welding process. The stirring pin effectively improved the interfacial reaction at the Mg/steel dissimilar metal. A thin accumulation layer of the Al was observed along with the interface. Discontinuous oxides of Mg appeared in the interface and were mainly distributed in the upper and bottom interfaces of the joint. As the heat input increased, the metallurgical bonding of the Mg/steel interface became stronger, and the joint strength increased. But when the heat input increased to a certain level, the oxidation of the Mg/steel interface became serious. The aggregation of MgO in the Mg/steel interface led to cracks, which decreased the joint strength. When the welding speed was 75 mm/min and the rotation speed was 850 rpm, the highest tensile strength of the joint was 189.4 MPa, which is 75.8 % of magnesium alloy. The joint fractured in the Mg side near the Mg/steel interface.

In this study, friction stir butt welding of ultra thin 430M2 ferritic stainless steel sheets with satisfactory joint properties has been achieved using a pinless WC-Co tool. Friction stir welding was carried out at a tool rotational speed of 900 rpm and a travel speed of 96 mm/min. FSW joints were welded completely without any unwelded zone resulting from smooth material flow, despite of being adopted pinless tool. It was revealed that the maximum tensile strength of FSW welds was 468 MPa, equivalent to the tensile strength of base metal. Notably, it was found that sigma phase formation in FSW welds is suppressed compared with that of arc welds, resulting in improving joint strength. These results suggest that the low input process of FSW is an effective substitute for the conventional fusion welding GTAW in ultra thin ferritic stainless steel plate.

The heights of deformed interface and surface affected the tensile shear load of lap joints fabricated by friction stir welding. The influences of shoulder diameter, weld pitch and evolution of mechanical properties has been investigated experimentally. The heights of the softened surface decreased and the bonded area widened with increasing the SD. The interface transformed from a hooked shape to a flat interface with decreasing the WP. The peak load was obtained by increasing the SD and WP. Fractured positions were divided in two types, shear and tensile fracture. Shear fracture occurred at the interface which contains stir zone. Tensile fracture was observed at the thermo-mechanically affected zone of the top plate. The fracture mode indicating the peak load was the shear fracture rather than tensile fracture. This is because the exact position of shear fracture was where the base material penetrated the bottom plate. The larger SD and higher WP produced higher peak load because of widened bonded area and little deformation. But the peak load decreased inversely in case of the higher rotation speed over than 1500 rpm which means higher heat input conditions.

Recently friction stir processing (FSP) has shown keen interest to achieve superplasticity in different aluminum alloys. The pin profile of FSP tool is one of the important process parameter which controls the mechanical and metallurgical properties of stir zone (SZ), like other variables of tool rotational speed, travel speed, and tool tilt. The high strength 7075 aluminum (Al-Zn-Mg-Cu) alloy was subjected to FSP to investigate effects of pin profiles on the superplastic behavior. Three different polygonal pin profiles of square, pentagon and hexagon were used. Microstructure, microhardness and grain size measurements were performed for all FSP samples. Fine grain uniform microstructure without cavitation in the SZ was observed in sample produced by square pin only. All polygonal pin profiles indicated sticking of workpiece material around tool pin that resulted in non-uniform grain microstructure in the SZ. Hot tensile testing was carried out for square pin under the superplastic condition of 3 × 10 −4 s −1 and 400 °C to study the superplastic behavior. Uniform superplastic elongation of 227% was obtained in the gage region of the square pin sample.

Dissimilar lap joints for a low carbon steel (SS400) sheet with thickness of 2 mm on a 6061-T6 Al alloy sheet with thickness of 5 mm or 10 mm were created by a process called friction stir spot fusion welding (FSSFW) using an assembly-embedded rod (AER) tool under a downward force of 12 kN and a rotational speed of 1200 rpm at different dwell times. The Al alloy sheet was melted at the central area of the faying surface, so that two IMC layers were formed at this surface and identified as Fe 2 Al 5 and Fe 4 Al 13 , as detected by XRD and SEM images. The IMC thickness increased along with dwell time, but its increment rate became slower for IMC thickness larger than 25 μm. The failure load increased along with the IMC thickness, but the failure load decreased quickly for IMC thickness larger than 17 μm. It was able to achieve 18–22 kN for the thickness of the IMC layer in the range of 6–17 μm for a dwell time from 35–55 s. The larger the crack was, the smaller the failure load.

A series of welds were produced at various processing parameters in friction spot welded of AA6061-T6 to investigate hook formation and mechanical properties. Two different types of hook defect were identified based on the locations, which were closely associated to the plunge depth. The weld strength had a negative correlation with the hook height. An increase in rotational speed, joining time or plunge depth increased the hook height and resulted in lower weld strength. Increasing plunge depth might also bring a positive effect of weld strength as a result of increased effective shear area.

This study presents the development of an in-situ hybrid micro-manufacturing process for making a novel micro-tool for the fabrication of a high-precision micro-hole of 200 μm in diameter in difficult-to-machine material. The hybrid approach consists of rotary micro-EDM, micro-EDM peck-drilling, co-deposition, reverse micro-w-EDM, and micro-honing. These techniques can all be conducted on a single machining center allowing for in-situ micro-manufacturing. On the basis of the concept of a ‘machining center’, a horizontal/vertical dual-usage high-precision headstock and a hybrid work-tank with modularized design are devised. A novel micro grinding-tool which has an invert-tapered forked microstructure with central-symmetry and radial-elasticity is designed and fabricated using the hybrid processes. By applying the principle of cantilever beam support, the micro grinding-tool is employed for honing a micro-hole on SKD11 cold-working steel, achieving micro-scale material removal. All working coordinates are recorded during the process, the micro-tool and—workpiece do not need to be unloaded and repositioned until all planned tasks are completed. Experimental results demonstrate that flatness of the hole-wall, circularity, and surface roughness of the honed micro-hole are 1 μm, 0.5 μm and Ra0.032 μm, respectively. Approaches to the factors influencing formation and accuracy of the micro-tool involving surface topography, current density in co-deposition, wire tension, rotation speed in honing, and tool longevity are all evaluated in detail.

The effect of the rotational and welding speed on the residual stresses of dissimilar friction stir welds of aluminum alloys AA2024-T3 and AA6061-T6 were studied using X-ray Diffraction. The methodology used to obtain the residual stresses is presented in detail, including the measuring parameters and software corrections used. The proposed methodology allowed to obtained low scatter in the residual stress measurements as presented in the results. The most significant variations in the residual stresses behavior and magnitude were related with the modification of the rotational speed. The effect of increasing the rotational speed is a reduction in the magnitude of the longitudinal residual stresses. This was directly associated with the increase of heat input and the reduction of thermal mismatch between the different zones of the weld. The influence of the welding speed on the residual stress was not significant when compared with the effect of the rotational speed, generating only a slightly increment in the profile of the retreating side when it was increased.

A Si phase refining process involving phosphorus additions and a mechanical rotational barrel (MRB) is described. The microstructure of Al–20%Si alloys obtained under different pouring temperature and rotation speed was investigated. The average particle size of primary Si first decreased and then increased with the decrease of pouring temperature, meanwhile decreased continuously with the increase of rotation speed. Finest primary Si with size of about 15 μm was achieved when the rotation speed was 90 r/min and the pouring temperature was around 700–720 °C. The refinement and uniform distribution of primary Si were mainly attributed to the presence of AlP particles provided by the phosphorus addition, and chilling and stirring effects induced by the rotational barrel.

The effect of the rotational speed and dwell time on the joint interface microstructure and tensile-shear strength of friction stir spot welded Al-5083 aluminum/St-12 steel alloy sheets was investigated. Joining of the sheets was performed using an alternative friction stir spot welding (FSSW) process in which the welding tool tip did not penetrate into the lower steel sheet. Rotational speeds of 900 and 1100 rpm were applied in association with the dwell times of 5 to 15 s to weld the samples. Thermal history was recorded during the joining process. Interfacial microstructure, formation of intermetallic compounds (IMCs) at the joint interface and the fracture locations were studied using stereo, optical and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). The used alternative process was successful to join the sheets. For both of the applied rotational speeds, there were optimum dwell times (10 and 12 s for the rotational speeds of 1100 and 900 rpm, respectively) to reach the maximum failure loads. The increasing trend of the strength as a function of the dwell time was related to the formation of a thin intermetallic (IM) layer at the joint interface. The decreasing trend was attributed to the formation of a relatively thick IM layer at the joint interface as well as the grain growth of aluminum at the exit-hole periphery where the final fracture occurred. The IM reaction layer thickness of 2.3 μm was found to be a critical thickness. Compared to the rotational speed of 1100 rpm, stronger joints were achieved by application of 900 rpm rotational speed.

This work concerns the novel Metal Continuous Screw Extrusion process (MCSE). The process gives new opportunities for processing metal alloys, composites and novel multi-materials. By principle, one feeds granulated material into the screw extruder which compacts and extrudes the material in a continuous manner. The inherent deformation is very complex and based on empirical knowledge, a comprehensive quantitative model for the strain evolution through the main four stages of the process is formulated for the first time.Data from screw extrusion of an Al-5%Mg alloy using an extrusion die temperature of 410 °C and relatively low feeding rate, showed a total accumulated strain ∼15 in the current prototype set-up for a O10 mm profile. Granule feeding rate and screw rotation speed are considered the most influencing parameters regarding predicted accumulated strain. The latter increases with lower feeding rates and higher rotation speeds of the screw. Further design optimization of the screw extruder might be assisted by the current model.

A coupled thermo-mechanical model is developed for friction plug welding (FPW) process of AA2219 aluminum alloy, which is validated by the experimental results of the torque and temperature history. Both the deformation of plug and base metal are considered in this model. It is concluded that weak-bonding and unbonding is caused by the poor interface normal force and material flow based on the simulational and experimental results. Significant inhomogeneity in distribution of temperature, effective strain and effective stress is observed along the thickness direction of FPW joint, resulting in the inhomogeneity of microstructure and mechanical property. The peak temperature of bonding interface can reach 508 °C, which is 79% of the melting point of base metal. Higher welding force and rotational speed could promote material flow and improve interface normal force, which is beneficial to obtaining better connection.

In this study, the effect of the tool rotational speed on the microstructure evolution and its significance on the mechanical properties of friction stir welded 9Cr-1Mo (P9) steel is investigated, and its properties are compared with A-TIG welding process. Friction stir welding (FSW) was carried out at two different rotational speeds viz., 200 rpm and 500 rpm with the constant traverse speed of 30 mm/min using the W-La2O3 tool. The consequence of this study showed that irrespective of tool rotational speed, the better tensile properties are achieved by the FSW process, and it is comparable to the A-TIG welded joint. This study proved that FSW is a potential welding technique for welding of P9 steel, and also, there is scope to avoid PWHT by lowering the tool rotational speed (

This paper examines the use of pre-fabricated interlocking arms/threading in enhancing the strength of friction stir spot welded hybrid joints of AA2219/PP-C30S polypropylene polymer by varying parameter combination. The process involves the fabrication of a pre-threaded hole on the Al alloy prior to the joining process, and the threading/crest-pitch profile aids mechanical interlocking. The peak temperature, crest-pitch interlocked profiles, microstructural and mechanical properties of the joints were examined. The results show that an increase in the tool rotational speed increases the thickness of the reaction layer (between the Al and the polymer substrates), the shear-tensile load (268–540 N), and the cross-tensile load (171–321 N) of the hybrid AA2219/PP-C30S joint. A rise in rotational speed reduces the volume of the unfilled zone while the formation of interfacial crack/discontinuity is promoted. Adhesive bonding impedes the formation of discontinuity/crack at the interface of the Al alloy and the reaction layer. The fracture of the joint is controlled by the volume of the unfilled zone, adhesively bonded region, and crest-pitch interlocked region.

This study developed a new micro drill-grinding tool for precision micro-drilling of hard brittle materials, such as alumina ceramic and soda-lime glass, and analyzed the material removal mechanism of micro drill-grinding. A model of the micro drill-grinding force F z was built using a physical method based on the undeformed chip thickness h m . Experiments examining micro drill-grinding were conducted on a micro-machining desktop for micro drill-grinding. The failure modes and the lifespan of this new tool were investigated compared to the conventional micro-grinding method. The variation of the micro drill-grinding force was investigated, and the effects of rotation speed n g are discussed. The change law of F z was revealed based on experimental results, which also verified the scientific internal logic relation of the model that this study proposes. The brittle–ductile transition in the micro drill-grinding of hard brittle materials was investigated. A ductile regime propelling technology of a resin coating was proposed and successfully developed in this study. This paper demonstrated that this technology could effectively propel the ductile-regime of soda-lime glass in micro drill-grinding and reduce the fracture size. Experimental machining examples indicate that the average fracture size is reduced from 239.58 μm to 15.11 μm, and the ductile regime is propelled from 50 nm/rev to above 200 nm/rev. The technique and knowledge that this study proposes could provide a significant contribution to the precision micro-machining of hard brittle materials.

Single Point Incremental Forming (SPIF) is a sheet forming process characterized by advantages that include low-cost and part-shape-independent tooling, higher formability and greater process flexibility as compared to conventional sheet forming. While recent work has demonstrated the possibility of SPIF of polymers the effects of incremental depth and tool rotation speed, key process parameters in SPIF, have rarely been examined. This work experimentally examines how incremental depth and tool rotation speed affect the failure mode during forming, forming forces as well as the void structure and crystallinity of the formed material in polymer SPIF. The dependence of both tearing and wrinkling on the incremental depth and tool rotation speed is uncovered. It is shown that contrary to SPIF of metals, greater incremental depths result in increased formability in polymer SPIF, but this advantage is limited by the occurrence of sheet wrinkling at excessively high incremental depths. Further, the occurrence of sheet wrinkling depends not just on the incremental depth but also on the part shape being formed. Microstructural examination of the formed material shows that greater incremental depth results in greater void densities and that the material formed with SPIF has greater crystallinity than the unformed material. Additionally, it is shown that higher tool rotation speed can cause earlier onset of wrinkling. The implications of these observations on SPIF of polymers are discussed.

An experimental setup was designed to compare the principal process parametric relationships with the classical approach to friction surfacing with the addition of inductive heating. The production of the flash is described quantitatively and its influence on coating geometry and mass is presented. It was found that the coating mass and thickness decreased for an increase in the rotational speed of the consumable rod; the amount of flash produced by the consumable rod also increased. However, the e_ect of an increase in this rod contact pressure on the coating thickness is insignificant, whilst the coating mass decreases with rising pressure and the coating width increases coupled with an increase in flash production. Cross sections showed good bonding quality and mechanical interlocking at the bond interface. The substrate-coating interface showed a varying degree of mechanical interlocking and the presence of cavitations. Bond strength values applying shear and push-o_ testing of up to 106 MPa and 96 MPa, respectively, could be identified.

A twin-tool setup has been designed and fabricated to make a comparative study between twin tool and single tool using double pass in a friction stir welding process. Twin tool helps in generating high heat causing intense plastic deformation in the processed zone. Defect free weld depends not only on the rotational speed, but also on the combined effect of welding speed and rotational speed. Higher hardness profile is observed with higher welding and rotational speeds; defect-free joints are also observed in this combination. Further, SEM results confirm the existence of ductile failure with microscopic voids of different shapes and sizes.

Refill friction stir spot welding (FSSW-Refill) was used to produce solid-state joints in an automotive 5042 aluminium alloy. The influence of plunge depth, rotational speed, plunge rate and time on the microstructure and shear strength was investigated. The Statistica software package was used to correlate process parameters with the mechanical properties of the joints. The most significant variables are plunge depth and tool rotational speed, while volumetric defects have a small influence on the mechanical performance of the welds. Reducing the rotational speed from 1900 rpm to 900 rpm increased the bonding ligament length. For joints produced at a higher tool rotational speed (1900 rpm) the material flow was more vertical, i.e., towards the surface of the joint, the bonding ligament length was reduced and the shear strength was impaired.

Friction stir processing of AZ31 Mg alloy was investigated by numerical modeling and experiments. A CFD based, fully coupled, 3D, thermo-mechanical model was built to better understand the effect of process parameters on temperature, material flow and strain rate. In order to account for material softening phenomena at elevated temperatures and extremely high strain rates that occur during the FSP process, experimentally measured peak temperatures were utilized to introduce a correction function in the flow stress constitutive relation. The numerical results showed that rotational speed as compared to translational speed had a more dominant effect on temperature field and strain rate. In addition, the asymmetric material flow around the tool axis caused higher peak temperature and strain rate on the advancing side (AS), while the material in the path of tool pin was swept around the retreating side (RS). FSP experiments confirmed peak temperatures measured at sheet surface near shoulder perimeter on AS were always higher than corresponding RS peak temperatures, under the selected range of process parameters. In addition to thermo-mechanical aspects, the metallurgical characteristics of FSP i.e. mainly the grain size evolution was studied by optical and electron microscopy. Experiments revealed that the coarse bimodal microstructure of as-received AZ31 Mg was subdivided into a defect-free, fine grain microstructure at the rotational speed of 1000 rpm, while a defect-free but a relatively coarse and bimodal microstructure evolved in the material at rotational speeds higher than 1000 rpm. Furthermore, in the selected range of process parameters the increases in translational speed resulted in finer grain sizes without the formation of voids or defects.

Joints with fully amorphous structure can be obtained by selecting proper friction time and rotational speed. The optimum strength of the joint is close to that of the base bulk metallic glass (BMG), demonstrating a perfect bonding. Based on the analysis of the temperature distribution during the friction welding, an equation mentioning the critical friction time for retaining amorphous structure has been established. The experimental results prove the validity of the equation. Moreover, the temperature distribution in the friction interface has been studied by numerical simulation, aiming to provide a better understanding of the friction welding process and the microstructure in the interface. The simulation results further confirm the availability of the calculation results, thus can be helpful for designing the process parameters using other BMG systems.

Samples with one through three passes with 100% overlap were created using friction stir processing (FSP) in order to locally modify the microstructural and mechanical properties of 6082-T6 Aluminum Alloy. A constant rotational speed and three different traverse speeds were used for processing. In this article, the microstructural properties in terms of grain structure and second phase particles distribution, and also the mechanical properties in terms of hardness and tensile strength of the processed zone were addressed with respect to the number of passes and traverse speeds. The parameter combination which resulted in highest ultimate tensile strength was further compared with additional two rotation speeds. FSP caused dynamic recrystallization of the stir zone leading to equiaxed grains with high angle grain boundaries which increased with increasing the number of passes. The accumulated heat accompanying multiple passes resulted in increase in the grain size, dissolution of precipitates and fragmentation of second phase particles. Increasing the traverse speed on the other hand did not affect the grain size, yet reduced the particles size as well as increased the particle area fraction. Hardness and tensile test results of the stir zone were in good agreement where increasing the number of passes caused softening and reduction of the ultimate tensile strength, whereas, increasing the traverse speed increased the strength and hardness. Increasing the tool rotational speed did not have a significant influence on particle mean diameter, ultimate tensile strength and hardness values of the stir zone, whereas, it caused an increase in mean grain size as well as particle area fraction.

This paper proposes an alternative centerless grinding technique, i.e., through-feed centerless grinding using a surface grinder. In the new method, a compact centerless grinding unit, composed of a guide plate, an ultrasonic shoe, a blade, and their respective holders, is installed onto the worktable of a surface grinder, and the through-feed centerless grinding operation is performed as the workpiece located on the guide plate is fed into the space between the grinding wheel and ultrasonic shoe. The ultrasonic shoe, produced by bonding a piezoelectric ceramic device onto a metal elastic body, is tilted at a small angle so as to provide sufficient force to control the workpiece rotational motion and to feed the workpiece along its axis by the ultrasonic elliptic-vibration. In this paper, the workpiece motion control tests were carried out firstly to make sure that the workpiece rotational speed and through-feed rate can be exactly controlled by the ultrasonic shoe which is essential for performing high-precision grinding operations. Then, the effects of major process parameters such as the workpiece eccentric angle, the stock removal, the ultrasonic shoe tilt angle and the applied voltage amplitude on the machining accuracy (i.e. workpiece cylindricity and workpiece roundness) were clarified experimentally. The obtained results indicate that: (1) the workpiece rotational speed can be adjusted by changing the applied voltage amplitude, whereas its through-feed rate can be adjusted by changing both the applied voltage amplitude and the ultrasonic shoe tilt angle; (2) the optimum eccentric angle is 6°, and a larger stock removal, a smaller tilt angle, or a higher applied voltage is better for higher machining accuracy; (3) the workpiece cylindricity and roundness were improved from the initial value of 16.63 μm and 14.86 μm to the final ones of 1.49 μm and 0.74 μm under the optimal grinding conditions.

Hypereutectic Al–Si alloy-based composite pistons reinforced with SiC particles locally at the head were fabricated by centrifugal casting. The effects of various technique parameters, i.e., the slurry temperature of the alloy, the mold temperature and the rotation speed of the mold, on the particle segregation were investigated, and the macromorphologies and microstructures of pistons were observed. The mechanical properties, such as hardness and wear resistance along the axis of the piston and the thermal expansion coefficient at the piston head, were measured. The results showed that, (1) centrifugal casting can be used as a new and effective method in manufacturing pistons, and reasonable parameters were 850 °C, 600 °C and 800 rpm for the slurry temperature of the alloy, the mold temperature and the rotation speed of the mold, respectively; (2) the hardness values of pistons fabricated by centrifugal casting gradually increased from the piston skirt to the piston head, and the average hardness value in piston heads was improved by 23.7HRB over that of pistons fabricated by gravity permanent mold casting; (3) the piston heads showed excellent wear resistance, and the wear rate of piston heads decreased by 70.3% over that of the piston fabricated by gravity permanent mold casting; and (4) the average linear expansion coefficient of the piston head was 15.3 × 10−6 K−1 and decreased by 23.1% over that of pistons fabricated by gravity permanent mold casting.

Friction stir spot welding (FSSW) of Al alloy 6016-T4 sheet was evaluated using a conventional pin (CP) tool and off-center feature (OC) tool. Tool rotation speed and plunge depth were varied to determine the effect of individual process parameter on lap-shear separation load. Maximum separation load of about 3.3 kN was obtained by using a 0.2 mm shoulder penetration depth with 1500 rpm tool rotation speed for the CP tool and 2500 rpm for the OC tool. Three different weld separation modes under lap-shear loading were observed: interfacial separation, nugget fracture separation and upper sheet fracture separation. Microhardness profile for weld cross section indicated no direct relationship between microhardness distribution and separation locations.

This study examined the effects of the speed and force in centrifugal casting on the wedge castability of Ti–5 mass%Cu (Ti–5Cu) alloy and commercially pure titanium (CP-Ti). The Ti–5Cu alloy was prepared by argon-arc melting. Whole wedge-shaped acrylic patterns were prepared with either 15° or 30° angles and invested with a MgO-based material. The wedge specimens were cast using a centrifugal casting machine at rotational speeds of 600, 1000, 1250, 1500 and 3000 rpm. Mold filling, an index for a measure of castability, was determined as the missing length between the edge of the cast wedge and the theoretical acute tip of the triangle. CP-Ti was used as a control. An analytical model was developed to relate the mold-filling index to the surface energy and rotational speed. The experimental results indicate that the means of the mold-filling index of the 30° wedge angle were lower than those of the 15° wedge angle when compared for each corresponding metal and rotational speed. In each angle for CP-Ti, the means tended to reduce with increase in the rotational speed. The mold-filling index of 5% Cu titanium was found to be similar to that of CP-Ti, even for 15° wedge when the rotational speed was higher than 1250 rpm. The results suggest that dental prosthesis, which has narrow cross sections containing very narrow regions (for example, clasps of a denture), can be cast successfully by utilizing high rotational speed during centrifugal casting. The complex dependence of mold-filling index on wedge angle and rotational speed is explained on the basis of the analytical model and the dependence of the apparent surface energy on rotation speed.