Friction Stir Processing Samples Research Articles

Transition from Superplastic Behavior - Viscous Glide - Dislocation Climb - Power-Law Break down Regimes in Friction Stir Processed AA5083

5083 Al alloy was friction stir processed (FSP) at room temperature under various experimental conditions. Two rotational speeds of 430 and 850 rpm with a single traverse feed of 90 mm/min (430-90, 850-90) were used, to investigate the effect of rotation speed. Also, another feed rate of 140 mm/min was used with a rotational speed of 430 rpm (430-140), to investigate the effect of feed rate. The processing conditions resulted in three different grain sizes of 0.95, 1.6 and 2.6 μm depending on the FSP parameters. The deformation behavior of the FSP samples was investigated at 250 C at three strain rates of 10-4, 10-3 and 10-2 s-1. The values of strain rate sensitivity, m was determined, as a function of grain size, and it decreased from 0.45 to 0.33 to 0.18 with increasing the grain size. True activation energy was calculated as 63, 95, 157 kJ/mole for the grain sizes of 0.95, 1.6 and 2.6 μm, respectively. These calculated values are comparable to grain boundary sliding of magnesium in aluminum (69 – 78 kJ mol-1), magnesium in aluminum (~115 kJ mole-1) and aluminum lattice diffusion (~143 kJ mol-1 ). The change in the deformation mechanism with grain size was discussed in some details.

Wear properties of 5083 Al–W surface composite fabricated by friction stir processing

Friction stir processing (FSP) was used to incorporate tungsten particles in 5083 Al matrix to fabricate metal particle reinforced surface composites. The particles were uniformly dispersed in the matrix and the grain size was also refined by FSP. X-Ray diffraction analysis showed no intermetallic peak confirming that the tungsten particles remained in their elemental form. The composite surface layer exhibited considerably higher wear resistance compared to the base and friction stir processed (FSPed) alloy. The worn surface analysis revealed that the composite undergoes adhesive and oxidative type of mild wear at all the three loads whereas there was a transition to abrasive and delamination type of severe wear at higher loads in the base and FSPed samples.

Microstructural Evolution and Wear Resistance of Friction Stir-Processed AISI 52100 Steel

Friction stir processing (FSP) was successfully applied on AISI 52100 steel. The influence of process parameters on the microstructure and mechanical properties of the material was evaluated. It was observed that the initial ferritic-pearlitic microstructure of the base metal is transformed to the martensitic microstructure with retained austenite in the stir zone. The results also showed that microhardness and wear resistance of the FSP samples are, respectively, at least 2 and 15 times higher than those of the base metal. The improvement of the mechanical properties of FSP samples was attributed to their microstructural characteristics. The mechanisms controlling the wear behavior of the base metal and FSP samples were also discussed.

Superplastic Constitutive Equation Including Percentage of High-Angle Grain Boundaries as a Microstructural Parameter

Fifteen Al-Mg-Sc samples with subgrain/grain sizes in the range of 1.8 to 4.9 μm were prepared through the processing methods of friction stir processing (FSP), equal-channel-angular pressing (ECAP), rolling, annealing, and combinations of the above. The percentages of high-angle grain boundaries (HAGBs) of these fine-grained alloys were distributed from 39 to 97 pct. The samples processed through FSP had a higher percentage of HAGBs compared to other samples. Superplasticity was achieved in all fifteen samples, but the FSP samples exhibited better superplasticity than other samples because their fine equiaxed grains, which were mostly surrounded by HAGBs, were conducive to the occurrence of grain boundary sliding (GBS) during superplastic deformation. The dominant deformation mechanism was the same for all fifteen samples, i.e., GBS controlled by grain boundary diffusion. However, the subgrains were the GBS units for the rolled or ECAP samples, which contained high percentages of unrecrystallized grains, whereas the fine grains were the GBS units for the FSP samples. Superplastic data analysis revealed that the dimensionless A in the classical constitutive equation for superplasticity of fine-grained Al alloys was not a constant, but increased with an increase in the percentage of HAGBs, demonstrating that the enhanced superplastic deformation kinetics can be ascribed to the high percentage of HAGBs. A modified superplastic constitutive equation with the percentage of HAGBs as a new microstructural parameter was established.

Effect of Post Heat Treatment on the Microstructure and Microhardness of Friction Stir Processed NiAl Bronze (NAB) Alloy

NiAl bronze (NAB) alloy is prepared by using friction stir processing (FSP) technique at a tool rotation rate of 1200 rpm and a traverse speed of 150 mm/min. A post heat treatment is performed at the temperature of 675 °C. The effect of heat treatment on the microstructure and microhardness is studied. The results show that the microstructure of the FSP NAB alloy consists of high density dislocations, retained β phase (β′ phase) and recrystallized grains. When annealed at 675 °C, discontinuous static recrystallization (DSRX) takes place. The content of β′ phase gradually decreases and fine κ phase is precipitated. After annealing for 2 h, both the microhardness of the FSP sample in the stir zone (SZ) and the difference in hardness between the SZ and base metal decrease due to the reduction of the dislocation density and β′ phase, accompanying recrystallized grain coarsening. With further increasing of the annealing time to 4 h, the aforementioned difference in hardness nearly disappears.

Enhancing Corrosion and Wear Resistance of AA6061 by Friction Stir Processing with Fe78Si₉B13 Glass Particles.

The AA6061-T6 aluminum alloy samples including annealed Fe78Si9B13 particles were prepared by friction stir processing (FSP) and investigated by various techniques. The Fe78Si9B13-reinforced particles are uniformly dispersed in the aluminum alloy matrix. The XRD results indicated that the lattice parameter of α-Al increases and the preferred orientation factors F of (200) plane of α-Al reduces after friction stir processing. The coefficient of thermal expansion (CTE) for FSP samples increases at first with the temperature but then decreases as the temperature further increased, which can be explained by the dissolving of Mg and Si from β phase and Fe78Si9B13 particles. The corrosion and wear resistance of FSP samples have been improved compared with that of base metal, which can be attributed to the reduction of grain size and the CTE mismatch between the base metal and reinforced particles by FSP, and the lubrication effect of Fe78Si9B13 particles also plays a role in improving wear resistance. In particular, the FSP sample with reinforced particles in amorphous state exhibited superior corrosion and wear resistance due to the unique metastable structure.

English

In this study, SiC particles were incorporated by using Friction Stir Processing (FSP) into the 6351 aluminium alloy to form particulate composite materials. Sampels were subjected to constant rotational and traverse speeds of the FSP tool with and without SiC reinforcements. Microstructural observations were carried out by employing optical microscopy of the modifiedsurfaces. Mechanical properties were evaluated by tensile test on UTM. For the 100% overlapping, No.of passes caused grain modification in the processed zone. The tensile test results indicate an improvement of strength and Microhardness for Single Pass FSP samples and a reduction in the strength of FSP samples with increasing the No.of passes due to the dissolution of the hardening precipitates.

Effects of Friction Stir Processing Parameters and In Situ Passes on Microstructure and Tensile Properties of Al-Si-Mg Casting

Friction stir processing (FSP) was applied to modify the microstructure of an as-cast A356 alloy. The effects of rotation rate, travel speed, in situ FSP pass, FSP direction, and artificial aging on microstructures and tensile properties were investigated. FSP broke up the coarse eutectic Si phase into 2.5 to 3.5 μm particles and distributed them homogeneously, and resulted in the dissolution of the coarse Mg2Si particles and the elimination of porosity, thereby improving both the strength and the ductility of the casting. Increasing the rotation rate was beneficial to breaking up and dissolving the particles, but it contributed little to eliminating the porosity. The travel speed did not affect the size of the particles apparently, but lower speed was beneficial to eliminating the porosity. 2-pass FSP showed an obvious advantage in the microstructure modification and tensile properties compared with the single-pass. However, a further increase of FSP passes only resulted in slight improvement. The FSP direction of the following pass did not show distinct effect on the microstructure and tensile properties. After post-FSP artificial aging, the strengthening phase (β″-Mg2Si) precipitated, which increased the strength and decreased the ductility of the FSP samples.

Effect of friction stir processing on erosion–corrosion behavior of nickel–aluminum bronze

In the present investigation, effects of Friction Stir Processing (FSP) on Erosion–Corrosion (E–C) behavior of Nickel–Aluminum Bronze (NAB) were studied by weight-loss measurements and surface characterization using an impingement jet test system. After FSP, the initial coarse microstructure of the cast NAB was transformed to a fine structure, and the porosity defects were eliminated. In addition, different FSP structures were produced by each rotation rate. Microhardness measurements showed a marked increase in FSP samples depending upon the FSP parameters. E–C tests were carried out by erodent at kinetic energies about 0.45μJ and in 30°, 60° and 90° impact angles to simulate actual service conditions. The maximum weight-loss was observed in FSP samples and Scanning Electron Microscopy (SEM) results showed signs of brittle fracture mechanism in FSP samples. By gravimetric analysis, the degree of synergy was evaluated at 0.45μJ kinetic energy at normal impact angle and negative synergy result implies the presence of a protective film on all sample surfaces.

Effect of Friction Stir Processing on Microstructure and Mechanical Properties of a HPDC Magnesium Alloy

A high pressure die cast (HPDC) magnesium alloy was friction stir processed (FSP) at high rotation rates with different advancing speeds. The AZ91 plate was 3 mm thick and the pin had a truncated cone tip. The friction stir processing induced the disappearance of porosity (typical of the HPDC process) in the nugget zone but some tunnel defects were introduced. The presence of characteristic FSP zones is not obvious due to the low plastic deformation of this alloy. The stirred zone is very narrow around the tool and this makes the FSP difficult to occur in the whole thickness of the plate. Microhardness values and electrical conductivity are sensitive to stirred zone and differences arise according to FSP parameters. The grain size is refined and homogenized by FSP due to partial solubilisation and disappearance of the eutectic phase surrounding Mg-alpha. X-rays diffractometry was performed on FSP samples to index phases and calculate peak shifts of Mg-alpha.

Improvement in cavitation erosion resistance of AISI 316L stainless steel by friction stir processing

Commercial AISI 316L plates with the initial grain size of 14.8 μm were friction stir processed (FSP) with different processing parameters, resulting in two fine-grained microstructures with the grain sizes of 4.6 and 1.7 μm. The cavitation erosion behavior, before and after FSP, was evaluated in terms of incubation time, cumulative mass loss and mean depth of erosion. A separate cavitation erosion test was performed on the transverse cross section of a FSP sample to reveal the effect of grain structure. It was observed that FSP samples, depending on their grain size, are at least 3–6 times more resistant than the base material against cavitation erosion. The improvement in cavitation erosion resistance is attributed to smaller grain structure, lower fraction of twin boundaries, and favorable crystallographic orientation of grains in FSP samples. The finer the grain size, the more cavitation erosion resistance was achieved. Moreover, the microstructures of eroded surfaces were studied using a scanning electron microscope equipped with EBSD, and an atomic force microscope. The mechanisms controlling the cavitation erosion damage in friction stir processed AISI 316L are also discussed.

Effects of Processing Parameters on the Microstructures and Mechanical Properties of In Situ (Al3Ti + Al2O3)/Al Composites Fabricated by Hot Pressing and Subsequent Friction-Stir Processing

In situ (Al3Ti + Al2O3)/Al composites were fabricated in an Al-TiO2 system by the combination of hot pressing (HP) and friction-stir processing (FSP). The effects of HP and FSP parameters on the microstructures and mechanical properties of the in situ composites were studied. The Al-TiO2 reaction extent increased with increasing the temperature and holding time of HP. Subsequent FSP not only induced Al-TiO2 reaction, resulting in the formation of nanosized Al3Ti and Al2O3, but also rounded the polygonal Al3Ti particles formed during HP. The tensile strength of the FSP sample in which the Al-TiO2 reaction took place completely during HP was lower than that of the FSP samples in which the Al-TiO2 reaction took place hardly or partly during HP. For the FSP samples in which the Al-TiO2 reaction took place hardly during HP, the volume fraction of reinforcing particles increased with decreasing the traverse speed, resulting in the increase in tensile strength of the FSP samples. At a traverse speed of 25 mm/min, increasing the rotation rate from 1000 to 2000 rpm produced little influence on the microstructures and mechanical properties of the in situ composites. Additional 2-pass FSP in water refined the matrix grains, resulting in the significant increase in the tensile strength.

Effect of Annealing Heat Treatment on the Microstructural Refinement of Pure Copper by Friction Stir Processing

Recently, friction stir processing (FSP) was developed as an effective method to modify microstructural and mechanical properties of materials. During process, a rotating tool is inserted in a plate, providing frictional heating and mechanical mixing. In this investigation, the effect of annealing heat treatment on the microstructure characteristics of the nugget zone was investigated during friction stirs processing (FSP) of the pure copper. Plate with 4 mm thickness was friction stir processed at constant traverse speed of 45 mm/min and tool rotation speed of 700 rpm. Samples were processed in various annealing conditions. Results showed that by increasing the annealing duration from 45 to 180 minutes at annealing temperatures of 600°C and 800°C, the grain size and the hardness value of samples significantly decreased. At annealing temperature of 1000°C samples were exposed to extra heat, grains started to coarsen and hardness decreased. Ultrafine-grained microstructure in FSP samples was achieved using annealing heat treatment at annealing temperature of 600°C.

Achieving Large-area Bulk Ultrafine Grained Cu via Submerged Multiple-pass Friction Stir Processing

Large-area bulk ultrafine grained (UFG) pure Cu was successfully prepared by multiple-pass overlapping friction stir processing (FSP) under additional rapid cooling. Overlapping FSP did not exert a significant effect on the microstructure and mechanical properties of the FSP UFG Cu. Similar average grain size was achieved in the transitional zone (TZ) of the multiple-pass FSP sample compared to that in the nugget zone of the single-pass FSP sample, and the TZ exhibited a strong {111} 〈 112 〉 type A fiber shear texture. Very weak softening occurred in the TZ of the multiple-pass FSP UFG Cu, resulting in a relatively uniform hardness distribution throughout the whole processed zone. A high yield strength of ∼310 MPa and a uniform elongation of ∼13% were achieved in the bulk FSP UFG Cu. This study provides an effective strategy to prepare large-area bulk UFG materials.

Modification of long period stacking ordered phase and improvement of mechanical properties of Mg–Gd–Zn–Zr alloy by friction stir processing

The effect of friction stir processing (FSP) on the modification of microstructure and mechanical properties of Mg–14Gd–2.3Zn–0.6Zr (wt%) alloy has been investigated. The coarse long period stacking ordered (LPSO) phase at grain boundary in the alloy was successfully broken into fine particles (~1µm) due to the complicated deformation beneath the shoulder and around the pin. The grain size was also significantly refined from 23±4μm to 1.6±0.3µm through dynamic recrystallization (DRX) during FSP. Yield strength of the FSP sample was increased by ~30% probably due to the grain size and LPSO phase refinement as well as fine precipitation around the LPSO phase while the elongation decreased by ~39% maybe because of the heterogeneous microstructure.

Microstructure and mechanical properties of multi-pass friction stir processed aluminum alloy 6063

The effect of overlapping between consecutive passes of Friction Stir Processing (FSP) was examined on the microstructure, microtexture, and mechanical properties of Al 6063. FSP was carried out at three overlapping (OL) percentages, i.e. 25, 50, and 75, and at constant rotational and traverse speeds of the FSP tool. Microstructural analysis based on grain boundary misorientation distribution, grain size and microtexture were made by Electron Back Scattered Diffraction (EBSD), while mechanical properties were evaluated by microhardness and tensile tests. For the three OL percentages, similar grain refinement (in the range of 3–6μm) occurred in the processed zone. The microtexture measurements in the OL area show the formation of shear texture, having a stronger intensity of B/B¯ component by increasing the OL percentage. On the other hand, the tensile and microhardness tests indicate a reduction in the strength and microhardness of FSP samples with increasing the OL percentage due to the dissolution of the hardening precipitates. The overlapping effect was further evaluated on the thermal stability of microstructure, microtexture, and mechanical properties of FSP samples by applying solution heat-treatment and aging (SHTA). The results show that SHTA led to grain growth with an average grain size of 35μm. However, it caused limited weakening of the shear texture in the OL area with no sign of recrystallization. In addition, SHTA led to precipitate formation and thus restoring the strength and microhardness to the levels of the base metal.

Formation of long-period stacking ordered phase only within grains in Mg–Gd–Y–Zn–Zr casting by friction stir processing

Friction stir processing (FSP) was applied to Mg–Gd–Y–Zn–Zr casting, resulting in significant dissolution of large grain boundary eutectic β-Mg3RE and long-period stacking ordered (LPSO) phases. A fine-grained structure with a grain size of ∼2.4μm was developed in the FSP sample. Besides, fine LPSO lamellae with a width of ∼5 to ∼200nm were distributed only within the grains in the FSP sample, which is different from that observed in both solution-treated and other plastically deformed counterparts. Formation of such special structure is attributed to the high temperature severe plastic deformation generated by FSP. The FSP Mg–Gd–Y–Zn–Zr exhibited high mechanical properties with a yield strength of ∼345MPa and an elongation of ∼21.5%. This study provides an effective way for mechanical property optimization in LPSO-contained magnesium alloys.

Improvement of cavitation erosion resistance of a duplex stainless steel through friction stir processing (FSP)

The cavitation erosion (CE) resistance of an UNS S32205 duplex stainless steel (DSS) was improved through microstructural modification using friction stir processing (FSP). As-received material was processed using 200rpm and 100mm/min spindle and travel speeds, respectively. The cavitation erosion tests were performed in a vibratory apparatus according to ASTM G32 standard. The incubation period, the maximum erosion rate and the variation of surface roughness during the tests are reported and the results are compared with those obtained for the base metal samples (BMS). The worn surfaces were characterized using roughness measurements and scanning electron microscopy (SEM). After a CE testing time of 10h, FSP samples showed a 70% diminution of the mass loss when compared to the BMS. Moreover, a 200% enhancement of incubation time and 100% reduction in the erosion rate were achieved after FPS. The improvement of CE performance is related to the recrystallized and refined microstructure, as well as to the modification of the elongated α/γ interfaces.

Influence of Process Parameters on Microstructure and Mechanical Properties of Friction-Stir-Processed Mg-Gd-Y-Zr Casting

Mg-10Gd-3Y-0.5Zr (wt pct) casting was subjected to friction stir processing (FSP) at a constant rotation rate of 800 rpm and varied travel speeds of 25, 50, and 100 mm/minute. FSP resulted in the generation of fine-grained microstructure and fundamental dissolution of coarse Mg5(Gd,Y) phase at the grain boundaries, thereby enhancing the tensile properties significantly at both room and elevated temperatures. The grain size of the FSP samples decreased with the increasing travel speed, whereas the microstructure heterogeneity with the banded structure (onion rings) became evident at a higher travel speed. Tensile elongation of the FSP samples increased as the travel speed increased, whereas the highest strengths were obtained at the medium travel speed of 50 mm/minute. Higher strengths and greater elongations were observed for the FSP samples in the transverse direction (TD) than in the longitudinal direction (LD). After post-FSP aging, the strengths of the FSP samples were increased significantly with the TD and LD exhibiting the same strengths; however, the elongation was decreased remarkably with the TD having higher elongation than the LD. A variation of the tensile properties was discussed in detail based on the microstructure heterogeneity and fracture surfaces.

An XPS analysis of the oxide surface layers formed on a friction stir processed magnesium alloy

Friction stir processing (FSP) is a promising technique for improving plasticity of magnesium alloys through the homogenization and grain refinement of their structure. In this study, a magnesium alloy AZ31 has been processed by FSP to achieve an ultrafine grain size structure (700 nm), and the oxide films formed spontaneously on the surface of the FSP zone are compared with those on the unprocessed material. Chemical composition of the oxide films are analyzed by XPS.The natural oxide films, close to 36 nm, can be described as a structure of (MgO)/Mg(OH)2 with the outermost surface mainly formed by Mg(OH)2/MgCO3. About 5–7 at.% of Al3+ is distributed through the oxide layer. Segregated zinc enrichment (Zn 2p3/2 at 1021.4 eV) at the interface oxide/metal is found. The FSP samples show higher carbonatation degree at the surface and a lower segregated zinc percentage at the interface oxide/metal. Copyright © 2012 John Wiley & Sons, Ltd.