Friction Stir Processing Samples Research Articles

Impact of in-process cooling and tool rotation speed on the mechanical and microstructural characteristics of friction stir processed AA2024

Despite significant grain size refinement, friction stir processing (FSP) of heat-treatable aluminum alloys is found to degrade the alloys of strength and hardness qualities. The drop in strength brought on by coarsening or the dissolution of the strengthening precipitate(s) could not be made up for by the improvement in strength brought about by the refinement of grain size following FSP. In order to get around this, the current work looks into a practical method of heat rejection from the FSP zone in addition to grain size refinement during FSP of AA2024 to regulate the precipitate evolution. Under natural cooling, air cooling, and CO2 cooling conditions, friction stir processing (FSP) was used to change the microstructure of Solutionized AA2024 at three distinct rotation speeds of 750, 1180, and 1500 rpm (fixed traverse speed of 50 mm/min). The microstructural evolution (through optical microscopy and SEM) and mechanical properties of FSP samples under different conditions of rotation speed and cooling and their differences were mainly discussed. All the FSP samples have a higher Vickers hardness than the base metal (minimum variation of 16.79% and maximum variation of 41.05%). The maximum hardness, yield strength, tensile strength, and elongation have been obtained under air cooling conditions and a rotation speed of 1180 rpm, which is a result of the simultaneous and effective effect of grain boundary strengthening and precipitation hardening.

Comparison of the corrosion and cavitation erosion behaviors of the cast and surface-modified manganese-aluminum bronzes in sodium chloride solution

Modified layers with refined and homogenized microstructure were obtained on a cast manganese aluminum bronze (MAB) by friction stir processing (FSP) and laser surface melting (LSM). In 3.5% NaCl solution, a much more protective film was formed and uniform corrosion occurred for the two surface-modified MABs. The corrosion rate of the cast sample was reduced by a factor of 29.73% after FSP and 51.35% after LSM. The cavitation erosion (CE) rate of the cast MAB was about 1.83 and 3.07 times larger than that of the FSP and LSM samples, respectively. The CE resistance increment was highly attributed to the improved hardness and enhanced nano-indentation behavior after FSP or LSM. For each MAB, the CE resistance decreased with extended pre-immersion time. Compared with the result of the correspondingly freshly-prepared sample, the CE rate was raised by a factor of 36.22%, 42.97% and 44.00% after 30 days’ pre-immersion for the cast, FSP and LSM MABs, respectively. For the cast and FSP MABs, mechanical impact was the leading factor accounting for CE degradation. For the pre-corroded samples, corrosion damage at the β and κ phases weakened the mechanical properties and thus triggered more grievous material exfoliation under CE. For the LSM MAB, CE-corrosion synergy dominantly gave rise to the CE damage. Corrosion at grain boundaries after pre-immersion also deteriorated the CE performance. The LSM MAB possessed the highest corrosion and CE resistances because the fine single-phase microstructure reduced the galvanic corrosion effect and crack propagation tendency under CE impact.

Reverse effects of pre-deformation and traverse speed on the mechanical properties of friction stir processed pure copper

In the present work, the effects of pre-strain and traverse speed on the microstructural evolution and tensile behavior of friction stir processed (FSPed) pure copper were investigated. In the samples without pre-deformation (0% samples), with the increment of the traverse speed from 100 mm min−1 to 200 mm min−1, the grain size decreased from 5.2 to 2.5 μm due to heat input domination. In the 60% pre-rolled samples (60% samples), interestingly, with an increase in the traverse speed (from 100 mm min−1 to 200 mm min−1), the average grain size increased from 2.4 to 6.8 μm owing to the domination of deformation degree. With the increment of speed from 100 mm min−1 to 200 mm min−1 in the 0% samples, the YS and UTS increased from 158.6 and 244.6 MPa to 190.7 and 253.9 MPa, respectively, due to decrement in the mean grain size. In addition, the increment of speed from 100 mm min−1 to 200 mm min−1 in the 60% samples reduced the YS and UTS from 177.9 and 261.7 MPa to 138.9 and 234.8 MPa, respectively, due to the increase in the mean grain size. In the 0% FSPed copper, by increasing the speed, the depth and size of dimples reduced, while, in the 60% FSPed samples, when the traverse speed increased, the dimples became larger.

The Role of Friction Stir Processing Parameters and Hybrid ZrC/WC Reinforcement Particles in Improving the Surface Composite Dissimilar Matrix’s Dynamic Behavior and Microstructure Refinement

This study examined the impact of hybrid reinforcement particles, specifically zirconium carbide (ZrC) and tungsten carbide (WC), as well as the parameters of friction stir processing (FSP), on the microstructure, mechanical properties, and dynamic behavior of aluminum alloys. The hybrid particles were integrated into the aluminum alloy using friction stir processing (FSP). The fabricated metal matrix composites (MMCs) were characterized using optical microscopy, scanning electron microscopy (SEM), and dynamic mechanical analysis (DMA). The results showed that the FSP parameters and reinforcement particles played an important role in improving the grain refinement of the MMCs. This study’s results suggest that the FSP samples’ UTS can be maximized using a tool rotation speed of 600 rpm and a traverse speed of 30 mm/min. The grain refinement in the composite surface was attributed to the dynamic recrystallization during the friction stir processing (FSP) process. The reinforcement particles also acted as grain growth restrictors, further refining the grain size. This resulted in a 34% increase in ultimate tensile strength compared to AA2024 alloys and a 12% increase compared to AA7075 alloys. The composite surface also exhibited enhanced dynamic properties, with an increase in impact energy of 26%. The free vibration test showed that the hybrid reinforcement particles significantly improved the strength and damping capacity of the aluminum alloys, resulting in a high resonant frequency. This is important for applications such as vibration damping and noise reduction.

Investigation of Mechanical and Tribological Behaviors of MMC Fabricated through FSP

Researchers and various industries place a high value on metal matrix composites (MMCs) made using friction stir processing (FSP), which has superior and finer particle dispersion and also successfully displays equalized grains through dynamic recrystallization. In the present research work magnesium alloy AZ31 reinforced with MoS2 was successfully made using FSP. The FSP samples are fabricated at 1000, 1200 and 1400 RPM while the traverse speed of 70mm/min is kept constants for all the FSP samples. AZ31 has light weight and excellent weight to strength ratio for this reason it can be used in various application like Aerospace Industry, Ship building and automotive applications but it has limitation in wear resistance and AZ31 Alloy is reactive and can corrode easily in corrosive medium. The present work aim is to investigate the mechanical and tribological behavior of AZ31/MoS2 Metal Matrix Composite (MMC) and then compared the properties with the base alloy. Here the specimen AZ31 is reinforced with MoS2 and processed by FSP to improve the tribological behavior the pin on disk wear test is conducted to study the wear performance. To investigate the hardness of the specimen, the hardness test is performed on the Brinell hardness apparatus. The corrosion behavior of MMC is also investigated by the immersion test conducted with 3.5% weight NaCl solution for 24 hours. All these properties are then compared with base Alloy. The SEM analysis is also investigated to study the surface behavior.

An investigation on the fabrication and characterization of friction stir processed nano-HAp reinforced AZ91D magnesium matrix surface composite for bio-implants

In the present research, friction stir processed (FSPed) nano-hydroxyapatite reinforced AZ91D magnesium matrix surface composite has been developed with improved ultimate tensile strength (UTS) and biological performance, which are needed for the bio-implants. Nano-hydroxyapatite reinforcement with varying proportions (5.8%, 8.3%, and 12.5%) was introduced into the AZ91-D parent material (PM) by the grooving method with different grooves of 0.5, 1 & 1.5 mm of width and 2 mm depth machined on the surface of the PM. Taguchi's L-9 orthogonal array was employed to optimize the processing variables for enhancing the UTS of the developed composite material. The optimum parameters were discovered to be the tool rotational speed of 1000 rpm, transverse speed of 50 mm/min, and 12.5% reinforcement concentration. The results revealed that the tool rotational speed contributes the highest effect (43.69%) on UTS, followed by the reinforcement percentage (37.49%) and transverse speed (18.31%). The FSPed samples at the optimized parameter setting confirmed the enhancement of 30.17% and 31.86% in UTS and micro-hardness, respectively, compared to the PM. Cytotoxicity of the optimized sample was also found superior compared to the other FSPed samples. The optimized FSPed composite's grain size was 6.88 times smaller than the AZ91D parent matrix material. The improved mechanical and biological performances of the composites are attributed to the significant grain refinement and proper dispersion of the nHAp reinforcement in the matrix.

Corrosion behaviour of friction stir processed, metastable, dual-phase, Fe49.5Mn30Co10Cr10C0.5, multi-principal element alloy

The corrosion behaviour of Friction Stir Processed (FSPed), dual-phase, Multi-Principal Element Alloy (MPEA), Fe49.5Mn30Co10Cr10C0.5, was investigated. The microstructure of the alloy in the annealed condition consisted of Face Cantered Cubic (FCC) and Hexagonal Closed Pack (HCP) phases, with the HCP phase present as laminates inside the equiaxed FCC grain. Fine carbide particles were found to be precipitated at the grain boundaries and also inside the grains. FSP engendered a reduction in the grain size due to dynamic recrystallization and an increase in the fraction of strain-induced HCP phase in the microstructure. The potentiodynamic polarisation and Electrochemical Impedance Spectroscopy (EIS) studies showed that the one-pass FSPed sample exhibited best corrosion resistance compared to the annealed and two-pass FSPed samples. The reason for this was ascribed to two factors: the reduced grain size and the smaller fraction of the HCP phase induced by strain in the microstructure. Mott-Schottky results indicated the presence of n- type semiconducting passive layer on the surface of annealed and FSPed samples. The one-pass sample had the lowest defect density (ND value) compared to annealed and the two-pass FSPed sample. Scanning Electron Microscopy (SEM) studies performed on the annealed, one-pass and two-pass samples, after immersion in 3.5 wt% NaCl solution, revealed the presence of large number of pits and corrosion products in the annealed sample compared to that in the FSPed samples. Results obtained from X-ray Photoelectron Spectroscopy (XPS) studies confirmed the presence of iron oxide, chromium oxide, cobalt oxide, chromium & cobalt hydroxides as the major constituents, together with a low concentration of manganese, in the passive layer formed on the FSPed samples.

Thermal stability behaviors of ultrafine-grained Cu-Cr-Zr alloy processed by friction stir processing and rolling methods

In order to investigate the effect of different microstructures on thermal stability, the thermal stability behaviors of ultrafine-grained Cu-Cr-Zr alloy processed by friction stir processing (FSP) and cold rolling (CR) methods was contrastively investigated by comparing with pure copper in this study. In addition to the precipitate strengthening, the FSP and CR samples were mainly strengthened by high angle grain boundaries (HAGBs) and dislocations, respectively. When there were no precipitates in Cu matrix, the onset temperature of softening of CR sample was 50 °C higher than that of the FSP sample at the same strength increment. But the precipitates in the FSP and CR Cu-Cr-Zr samples stabilized the deformed microstructures and precipitate coarsening occurred before the recrystallization of deformed microstructures. Therefore, the thermal stability differences disappeared in the FSP and CR Cu-Cr-Zr samples with the same onset temperature of softening (400 °C). In Cu-Cr-Zr alloys, although the stored energy of the FSP sample (39.1 J/mol) was 17.1% higher than that of the CR sample, the activation energy (∼175 kJ/mol) for grain growth of FSP sample was the same as that for recrystallization of CR sample. The different decrease degrees of thermal stability caused by different stored energy are completely masked by the kinetic constraint of precipitates.

Modification of cold-sprayed high-entropy alloy particles reinforced aluminum matrix composites via friction stir processing

In this study, a kind of novel Al matrix composite reinforced by CoCrFeNi HEA particles was fabricated by cold spray (CS) and subsequent friction stir processing (FSP) for the first time. The microstructure and mechanical properties of cold-sprayed (CSed) and friction stir processed (FSPed) CoCrFeNip/6061Al composites were examined using scanning electron microscopy, energy dispersive spectroscopy, electron backscattering diffraction, X-ray diffraction, and hardness and tensile tests. The results demonstrated that CSed samples exhibited a number of micro-pores in the Al matrix with homogeneous distribution of HEA particles, but heterogeneously distributed grain size. Continuous dynamic recrystallization and geometric dynamic recrystallization occurred at the interface between the HEA particles and Al matrix. Following FSP, the micro-pores were eliminated, and a small amount of HEA particles was fragmented and uniformly dispersed in the Al matrix. Moreover, the average size of HEA particles was refined from ~21–14 µm. The Al matrix exhibited dynamic recrystallization and particle-stimulated nucleation recrystallization, thus resulting in an average grain size of ~1.9 µm. Obvious diffusion layers of 0.5 µm and 1 µm in thickness occurred at the interface between the HEA particles and Al matrix in CSed and FSPed samples, respectively. A new phase with a body-centered cubic structure was confirmed to be an HEA in diffusion layers. Compared with CSed samples, the microhardness, ultimate tensile strength, and elongation of the FSPed samples increased by 91%, 60%, and 130%, respectively. The improved mechanical properties are attributed to the high density and enhanced interfacial bonding. Thus, this study provided a novel method for preparing high-performance Al matrix composites reinforced by HEA particles.

Mechanical properties and corrosion behavior of a friction stir processed magnesium alloy composite AZ31B–SiC

Abstract The optimization of friction stir processing (FSP) parameters of magnesium alloy composite (AZ31B–SiC) based on orthogonal test was researched. The results show that the distribution of silicon carbide (SiC) particles, microhardness, tensile property, and fracture mode are greatly affected by the change in process parameters. The results show that the composite was made with a rotating speed of 750 rev·min−1, a traversing speed of 30 mm·min−1, and a processing time of three; the distribution of SiC particles is even, the microhardness difference of composite is small, the tensile property is better, and the ductile fracture is the main fracture mode. Besides, the existence of SiC and the number of FSP have a certain influence on the corrosion performance of the magnesium alloy composite (AZ31B–SiC), and the corrosion resistance of the FSP sample is obviously better than that of the AZ31B magnesium alloy.

Revisiting copper as a case study of creep in pure metals: Prediction of creep response in pure Cu in half-hard and friction-stir-processed states

A physical model was used to obtain a pre-assessment of the dependence of minimum creep rate on stress and temperature for ETP copper under two different initial conditions, i.e., in the R240 half-hardened state and after friction stir processing. Although the R240 samples contained a high dislocation density owing to pre-straining, the material that underwent friction stir processing (FSP) had a much finer grain size and a far lower dislocation density.The original Sandström physically based model developed for copper was modified to take into account the strengthening role of the grain boundaries, and its declining importance with increasing temperature and/or decreasing applied stress. In addition, the grain growth effect was estimated using appropriate empirical equations. The model curves obtained by introducing a few initial information, such as the grain size and the ultimate tensile strength at room temperature, in the resulting set of constitutive equations, largely overlapped. This finding was somewhat in conflict with the traditional view, which assumes that a fine grain size is an ineffective source of creep strengthening, if not detrimental.Subsequent creep experimental testing carried out between 178 and 355 °C substantially confirmed the picture provided by the pre-assessment, and the minimum creep rate values for the two materials largely overlapped on the same curves. Only at 355 °C did the FSP samples exhibit a somewhat higher creep rate, when compared with the R240 samples and the pre-assessment curve. The experimental data obtained for R240 copper at 475 °C were not properly described by the physical model, as expected on the basis of the previous literature reports.

Effect of friction stir processing on microstructures and mechanical properties of TIG cladding layer on AA7075

AA7075 is a precipitation strengthened Al-Zn-Mg-Cu alloy which has been widely used. As a common way to repair AA7075 components, tungsten inert gas (TIG) cladding generates coarse grains and defects. In addition, the use of other types of filler wires could lead to insufficient rigidity and strength of the cladding layer. In the present work, friction stir processing (FSP) has been applied to the TIG cladding layer on AA7075 to study the effect of process parameters on microstructures and mechanical properties. The macro/micro structural characteristics, elemental distribution, microhardness distribution and tensile properties have been investigated. The macroscopic defects in TIG cladding layer are eliminated and the size of grains is decreases to around 6 μm by FSP. FSP reduces the compositional difference between the stir zone and the base material. Higher rotational speed promotes the grain refinement while the lower traverse speed benefits the microstructural uniformity. FSP on the TIG weld bead brings improvement in tensile properties and hardness. All the fractures for TIG + FSP samples occur at thermo-mechanically affected zone of the advancing side. The tensile strength of the stir zone increases from 424.2 to 442.8 MPa with the increase in rotational speed and traverse speed.

Machine learning application for evaluating the friction stir processing behavior of dissimilar aluminium alloys joint

This paper reports on the employment of the machine learning (ML) techniques, namely support vector machine (SVM), artificial neural networks (ANN), and random forest (RF), for predicting the tensile behavior of friction stir processed (FSP) dissimilar aluminium alloys joints (6083-T651 and 8011-H14). The dissimilar aluminium joints are fabricated using the friction stir welding (FSW) process. After that, the friction-stir welded joints are subjected to the FSP procedure at different combinations of process parameters. The rotational speed, traverse speed, and tilt angle are used as the input parameters, while tensile strength and grain size are used as the output parameters. In addition, three performance characteristics (i.e., coefficient of correlation (CC), mean absolute error (MAE), and root mean square error (RMSE)) are used to check the adequacy of the developed model of ML techniques. It is observed that support vector machine_radial basis function kernel is the most accurate modeling technique for predicting the tensile behavior of processes samples. Furthermore, the optical microscope is also utilized to check the grain size of the nugget zone (NZ) of the weld bead for FSP. It is found that the minimum grain size (i.e., 5.06 µm) is obtained for the FSP sample and this grain size corresponded to the high ultimate tensile strength (UTS). Moreover, the fractographic analysis showed the ductile behavior of FSW and FSP samples.

Effects of different cooling conditions on friction stir processing of A356 alloy: Numerical modeling and experiment

In the present work, the effects of in-process cooling are investigated on the material flow, temperature distribution, axial force, wear resistance, and microstructural and mechanical properties of friction stir processed (FSPed) Al-Si aluminum alloy. The finite element method (FEM) was developed for modeling the process, based on the eulerian-lagrangian technique, and then verified by the experimental force and temperature histories. Next, the material flow and temperature distribution during the friction stir process (FSP) with in-process cooling under different conditions were considered. After that, the experimental investigations, including the optical microscopy, hardness, and wear tests, were conducted. Finally, the stir zone (SZ) shape obtained by experiments and simulation model were compared for the FSPed samples without cooling and with air cooling. The material flow achievements reveal that using a coolant affects the material flow in the pin-driven zone more significantly than in the shoulder-driven zone, leading the SZ to change from the basin shape into the V shape. The SZ shapes obtained from the experiments and the simulation model show a good agreement between the shapes of the samples FSPed without cooling and with air cooling. Moreover, experimental results showed that using in-process cooling reduces Si particles' size and thus significantly increases the hardness and wear resistance. The Si particles size is reduced from 10 μm in the base metal to 2.6 μm and 2 μm in the air-cooled and water-cooled samples. Consequently, the wear mass loss reduced almost 28% and 40%, and hardness increased almost 35% and 80% for the air-cooled and water-cooled samples compared to the processed samples without coolant.

Microstructure, hardness, and wear resistance of AZ91 magnesium alloy produced by friction stir processing with air-cooling

Friction stir processing (FSP) was used to modify the surface layer of the AZ91 magnesium alloy. The treatment was carried out using a jet cooling nozzle, generating a stream of cold air and enabling intensive cooling of the friction stir processed (FSPed) zone. Single-pass FSP was carried out using a tool rotational speed of 500 rpm and travel speed of 30 mm/min. The treatment was conducted using a truncated cone-shaped tool with a threaded side surface. Strong grain refinement and microstructural changes typical for FSP were found in all the samples. Very fine, equiaxed recrystallized grains dominated in the stirring zone. In the samples modified with the jet cooling nozzle, greater grain refinement was obtained than in the case of naturally cooled material. The average grain size in the surface part of the stirring zone was 1.4 μm and 9 μm in the samples with air-cooling and with natural cooling, respectively. Both the naturally cooled specimen and air-cooled specimen were characterized by a distinctly higher hardness than the base material. The average Vickers hardness in the stirring zone was 91 HV0.1 in the FSPed sample with the air-cooling system and 85.5 HV0.1 with natural cooling, respectively. The average Vickers hardness of the as-cast alloy was 64 HV0.1. Slightly higher wear resistance of the FSPed samples using a jet cooling nozzle was found in relation to the naturally cooled sample. Based on the conducted research, high efficiency of the jet cooling nozzle in cooling the modified zone during friction stir processing was found.

Experimental Investigation of the Friction Stir Weldability of AA8006 with Zirconia Particle Reinforcement and Optimized Process Parameters.

A lightweight, highly corrosive resistant, and high-strength wrought alloy in the aluminum family is the Aluminium 8006 alloy. The AA8006 alloy can be formed, welded, and adhesively bonded. However, the recommended welding methods such as laser, TIG (Tungsten Inert Gas welding), and ultrasonic are more costly. This investigation aims to reduce the cost of welding without compromising joint quality by means of friction stir welding. The aluminum alloy-friendly reinforcement agent zirconia is utilized as particles during the weld to improve the performance of the newly identified material AA8006 alloy in friction stir welding (FSW). The objectives of this research are to identify the level of process parameters for the friction stir welding of AA8006 to reduce the variability by the trial-and-error experimental method, thereby reducing the number of samples needing to be characterized to optimize the process parameters. To enhance the quality of the weld, the friction stir processing concept will be adapted with zirconia reinforcement during welding. The friction stir-processed samples were investigated regarding their mechanical properties such as tensile strength and Vickers microhardness. The welded samples were included in the corrosion testing to ensure that no foreign corrosive elements were included during the welding. The quality of the weld was investigated in terms of its surface morphology, including aspects such as the dispersion of reinforced particles on the welded area, the incorporation of foreign elements during the weld, micro defects or damage, and other notable changes through scanning electron microscopy analysis. The process of 3D profilometry was employed to perform optical microscopy investigation on the specimens inspected to ensure their surface quality and finish. Based on the outcomes, the optimal process parameters are suggested. Future directions for further investigation are highlighted.

Effect of microstructure and precipitate formation on mechanical and corrosion behavior of friction stir processed AA6061 alloy using different cooling media

The present work studies the effect of microstructure and precipitate formation on mechanical and corrosion characteristics of friction stir processed AA6061 alloy using different cooling technologies (cryogenic and water cooling). The results revealed that recrystallized fine grains formed in all friction stir processing samples (grain size within a range of 2–6 µm) as a result of dynamic recovery and recrystallization, while samples processed in cooling-assisted friction stir processing resulted in better grain refinement in the stir zone than in air-cooled friction stir processing. Three kinds of precipitates (Fe-based needle-shaped precipitates, Si-based round-shaped precipitates, and chain of small round-shaped Si-based precipitates) were identified in base material and friction stir processing samples. Compared to air-cooled friction stir processing, in cooling-assisted friction stir processing, the hardness and tensile strength increased but remained lower than for the base alloy due to the presence of high density Fe-based needle-shaped precipitates. The ductility after friction stir processing greatly improved due to thermal softening and dissolution of precipitates. The corrosion results demonstrated that the corrosion resistance greatly enhanced after friction stir processing due to uniform distribution of grain structure and discontinuous chain of small round-shaped Si-based precipitates in stir zone. Moreover, cooling-assisted friction stir processing resulted in improved corrosion resistance compared to air-cooled friction stir processing due to the formation of fine precipitates.

Effect of Heat Treatment on the Microstructure, Mechanical Properties, and Corrosion Resistance of Friction Stir Processed Al-Zn-Mg-Cu-Sc-Zr Alloy

Post-heat treatment was conducted on the Al-Zn-Mg-Cu-Sc-Zr alloy treated by friction stir processing (FSP) to optimize its strength and corrosion resistance. Different post-heat routes had significant bearing on the phase composition of the FSP sample, while its fine equiaxed grain structure could be retained during post heating. Enhanced strength of the FSP sample was obtained by post-heat treatments. The FSP sample after T6 treatment (artificial aging to peak hardness value after solid solution treatment) exhibited the highest strength in virtue of its high precipitation strengthening effect, and the high ductility of the FSP sample could be retained after solid solution treatment. Furthermore, the FSP sample presented better corrosion resistance after artificial aging and T6 treatment by reducing its solution atom numbers.

Optimizing the mechanical properties of Al–Si alloys through friction stir processing and rolling

In this study, hypoeutectic and eutectic Al–Si alloys were processed through rolling and friction stir processing (FSP), and the effects of deformation routes on the microstructures and mechanical properties of Al–Si alloys were studied. FSP led to the fragmentation and uniform distribution of Si phases in the Al matrix and then eliminated the preferential crack propagation channels of Al–Si alloys during tensile tests. The optimized crack propagation path and high work hardening rate led to a tensile elongation of as high as 39% in FSP Al–7Si alloys. Further rolling refined the Al grains and introduced dislocations into the Al–Si alloys. The fine Si phases, tens of nanometers is size, in the FSP samples promoted grain refinement after rolling. Compared with the Al–Si alloys subjected to warm rolling only, the alloys subjected to FSP and warm rolling exhibited higher strength and ductility. FSP alloys with the highest strength were achieved through cold rolling because of high grain boundaries and dislocation-strengthening effects. This work provided a method for fabricating Al–Si alloys with excellent mechanical properties by combining FSP and rolling.

Effect of cryogenic treatment on corrosion behavior of friction stir processed magnesium alloy AZ91

The effect of cryogenic treatment on corrosion behavior of Friction Stir Processed (FSPed) Magnesium alloy AZ91 is investigated. FSPed samples are treated by Deep Cryogenic Treatment (DCT) and the NaCl immersion test is conducted to study the corrosion behavior of AZ91 alloy. The immersion test results confirmed that the corrosion resistance of cryogenically treated FSPed AZ91 Mg alloy samples is improved to a greater extent as compared to that of an as-received AZ91 alloy sample and FSPed AZ91 Mg alloy samples. The corrosion resistance of AZ91 Mg alloy and its mechanical properties are mainly improved due to the scattering of particles with DCT. The structure of the as-received AZ91 alloy changed from disorderly solid solution to orderly solid solution after DCT.