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Microstructures of a) base metal, b) NHT stir zone, c) NHT heat affected zone, d) HT stir zone e) HT heat affected zone.
![Fig. 2. Dimensions of tensile specimen [6].](publication/335027554/figure/fig2/AS:789430289838081@1565226256736/Dimensions-of-tensile-specimen-6_Q320.jpg)
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... microstructures of the base metal, non-heat treated stir zone (NHTSZ), non-heat treated heat affected zone (NHTHAZ), heat treated stir zone (HTSZ) and heat treated heat affected zone (HTHAZ) are shown in Fig. 3 (a)-(e). The optimized process parameters resulted in defect-free microstructure. The microstructure of base metal displays coarse grains of aluminum matrix along with small volume fraction of precipitates at grain boundaries with a grain size of 107 μm (Fig. 3 (a)). The microstructure of NHTSZ reveals the presence of small recrystallized ...
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... heat treated stir zone (HTSZ) and heat treated heat affected zone (HTHAZ) are shown in Fig. 3 (a)-(e). The optimized process parameters resulted in defect-free microstructure. The microstructure of base metal displays coarse grains of aluminum matrix along with small volume fraction of precipitates at grain boundaries with a grain size of 107 μm (Fig. 3 (a)). The microstructure of NHTSZ reveals the presence of small recrystallized grains of 3.87 μm (Fig. 3 (b)). These results attributed to the occurrence of intense plastic deformation at tool-work interface leads to dynamic recrystallization in the stir zone of NHT specimen and resulted in fine grains. From the microstructure of HTSZ, it ...
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... optimized process parameters resulted in defect-free microstructure. The microstructure of base metal displays coarse grains of aluminum matrix along with small volume fraction of precipitates at grain boundaries with a grain size of 107 μm (Fig. 3 (a)). The microstructure of NHTSZ reveals the presence of small recrystallized grains of 3.87 μm (Fig. 3 (b)). These results attributed to the occurrence of intense plastic deformation at tool-work interface leads to dynamic recrystallization in the stir zone of NHT specimen and resulted in fine grains. From the microstructure of HTSZ, it was observed that there is no much grain coarsening after heat treatment ( Fig. 3 (d)). The grain size of ...
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... grains of 3.87 μm (Fig. 3 (b)). These results attributed to the occurrence of intense plastic deformation at tool-work interface leads to dynamic recrystallization in the stir zone of NHT specimen and resulted in fine grains. From the microstructure of HTSZ, it was observed that there is no much grain coarsening after heat treatment ( Fig. 3 (d)). The grain size of HTSZ was measured to be 3.9 μm which is almost similar to the NHTSZ. As expected, the heat-affected zones of heat treated and non-heat treated specimens show the marginal increment in grain size and approximately same as the grain size of the base metal (Fig. 3 (c & d)). This is due to the excess heat input and ...
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... that there is no much grain coarsening after heat treatment ( Fig. 3 (d)). The grain size of HTSZ was measured to be 3.9 μm which is almost similar to the NHTSZ. As expected, the heat-affected zones of heat treated and non-heat treated specimens show the marginal increment in grain size and approximately same as the grain size of the base metal (Fig. 3 (c & d)). This is due to the excess heat input and absence mechanical stirring. ...
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... A popular aluminum alloy with a high strength-to-weight ratio, great fatigue resistance, and strong corrosion resistance is called Al-Cu alloy. Traditional fusion welding techniques, however, can result in a number of problems, including porosity, solidification cracking, and diminished mechanical qualities in Al-Cu alloy [14][15][16][17][18]. FSW offers a strong substitute with many benefits in terms of weld performance and quality. ...
Friction stir welding (FSW) has gained prominence in the aerospace and automotive industries due to its ability to produce high-strength and defect-free welds in aluminum alloys. The present investigation focuses on the impact of different tool rotational speeds (such as 700 rpm, 900 rpm, 1100 rpm and 1300 rpm), on the microstructure and mechanical characteristics of friction stir welded Al-Cu alloys. With the use of optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and evaluations of hardness, tensile characteristics, and fracture behavior, a thorough analysis was carried out. The weld nugget zone contained significant changes in grain size and shape as a function of rotational speed, as shown by microstructural analysis. The grain structure gradually became more refined when the rotating speed was raised from 900 to 1500 rpm. According to SEM observations, at faster speeds, the weld zone showed fewer defects per unit area and better bonding properties, which might be attributed to better material flow and plastic deformation. The effect was further clarified by XRD analysis, which showed differences in phase composition with varying rotating speeds. Evaluations of the mechanical properties showed a significant relationship between rotating speed and the mechanical performance of the welds. Hardness measurements showed that as rotating speed increased, hardness levels gradually increased. Welds made at faster rotational speeds had better elongation and tensile qualities, according to tensile tests. Additionally, fracture behavior study revealed that higher rotational speed welds displayed a more ductile fracture mode, indicating increased toughness.
... These findings International Journal of Metalcasting suggest that severe plastic deformation at the tool-work interface occurred, which caused DRX in the processed sample's stir zone and produced fine grains. 22,23 The formation of the equiaxed grain structure after FSP is attributed to the dissolving and quicker re-precipitation of second-phase particles and Al 2 CuMg precipitates in this alloy, as well as to their homogeneous distribution along the GBs. 14,24 Despite the fact that the temperature created by FSP is much higher than is required for aberrant grain growth to occur, this prevents grains from growing any further. ...
Friction stir processing (FSP) is the most effective severe plastic deformation process for creating materials with very fine grains and good properties. The target of the present research is to investigate the influence of FSP on the microstructure and mechanical properties of homogenized 2024 aluminum alloy with and without rare-earth (RE) and thermomechanically treated conditions (TMT). The rare-earth elements used were Ce and La in the form of a master alloy containing (50% Ce + 50% La). The casting of 2024 aluminum alloys, both with and without (Ce + La), was carried out using the conventional stir cast technique. Part of the obtained alloys was homogenized, whereas the other part was thermomechanically treated (TMT). The homogenized 2024 material was exposed to FSP with multiple passes (one, two, and three) to obtain the suitable pass number. After that, the best pass number was performed on the 2024 aluminum alloy refined with RE (Ce + La) and TMT materials. The microstructures in different conditions (homogenized and stir friction) were examined by optical and scan microscopes attached with EDS and Map analyzer. At the same time, a tensile test was conducted to assess the mechanical properties. The findings indicated that the microstructures were significantly refined after adding RE (Ce + La) or applying the TMT technique. Whereas, the microstructures were greatly improved after applying FSP to both conditions. Ultra-fine grains were observed for both TMT and RE-containing alloys after FSP. On the other hand, the results of mechanical properties were significantly increased after applying multiple passes of FSP. The optimum results were obtained when two passes of stir friction were applied to the TMT alloy condition.
... Al2014 is more vulnerable to corrosion attacks due to copper degradation than other aluminum series alloys. 16,17 The literature indicates that corrosion studies on friction stir processed Al2014 are scarce. Therefore, the present study aimed to investigate the impact of cooling media on the corrosion behavior of friction stir processed Al2014 alloys. ...
The current work investigates the influence of different cooling media (i.e., air, dry ice, and water) on the electrochemical behavior of friction stir processing (FSP) of Al2014 alloy. After FSP, recrystallized fine grains were developed in the stir zone due to severe plastic deformation and dynamic recrystallization. The average grain size in air-cooled, dry ice-cooled, and water-cooled FSPed samples were found to be 4.6 ± 3.2 lm, 4.1 ± 2.8 lm, and 0.89 ± 0.6 lm, respectively. Due to the faster cooling effect, grain coarsening was inhibited, resulting in the development of the ultrafine grain (UFG) structure in a water-cooled FSP sample. The stirring action of the tool causes the fragmentation of Al 2 Cu precipitates into fine and discontinuous particles after FSP, and water-cooled FSP ($ 0.7 lm) resulted in very fine precipitates compared with air-cooled ($ 0.92 lm) and dry ice-cooled FSP ($ 0.8 lm). The corrosion findings showed that the corrosion resistance was enhanced after FSP (E COR = 851 mV) due to the formation of homogeneously formed refined grain structure and discontinued fine Al 2 Cu precipitates. Among the FSP samples, better corrosion resistance was obtained for the water-cooled FSP sample (E COR = À 685 mV) due to the formation of UFG structure and very fine precipitates.
... They used tools with different pin profiles and found increased hardness and better grain refinement after the process. Satyanarayana and Kumar [26] performed multi-pass FSP on AA2014 and post-heat treatment was applied over its surface to improve its mechanical properties. They found that the properties of the heat-treated FSPed samples were enhanced after the process. ...
The present study aimed to improve the micro-hardness and wear properties of AA2014 aluminum alloy. Surface composite of AA2014 was produced using Al 2 O 3 as reinforcement by friction stir processing (FSP) technique. FSP was performed by using a constant traverse speed of 40 mm/min and two rotating speeds of 1000 and 1400 rpm. After FSP, the average grain size of AA2014 was reduced from 21.9 µm in base material to 9.2 µm in FSP with a rotating speed of 1000 rpm and 3.8 µm in FSP with rotating speed of 1400 rpm. Optical microscopy showed that the Al 2 O 3 reinforcement particles were distributed homogeneously in AA2014 after FSP. The micro-hardness test showed that the hardness property in AA2014/Al 2 O 3 surface composite was improved after FSP and was increased with an increase in rotating speed. The micro-hardness was improved by 30% after FSP. The wear test revealed that both the wear performance and coefficient of friction (COF) were improved after FSP. The COF was improved from 0.27461 in base material to 0.22570 in FSPed samples. Surface roughness test showed that the sample with more micro-hardness showed better surface roughness as compared to the other samples.
... Additionally, looking at the hardness of the stir zone to the AA8011 base material of the 3-pass SFSP for the specimen extracted towards the end of the joint, it can be seen that it was notably lower due to the defects on the position as a result of being cut too close to the SFSP tool exit hole. This is due to the submerged conditions preventing the material softening and coarsening of the grains [17,[23][24][25]. The 1-pass hardness of the stir zone maximum hardness was found to be 75 HV, 65 HV for the 2-pass, 65 HV for the 3-pass and 67 HV for the 4-pass specimen. ...
... Additionally, looking at the hardness of the stir zone to the AA8011 base material of the 3-pass SFSP for the specimen extracted towards the end of the joint, it can be seen that it was notably lower due to the defects on the position as a result of being cut too close to the SFSP tool exit hole. This is due to the submerged conditions preventing the material softening and coarsening of the grains [17,[23][24][25]. The 1-pass hardness of the stir zone maximum hardness was found to be 75 HV, 65 HV for the 2pass, 65 HV for the 3-pass and 67 HV for the 4-pass specimen. ...
The AA6082-AA8011 friction stir-welded joints were subjected to submerged multiple pass friction stir processing to evaluate the microstructure and mechanical properties of the joints. A maximum of four submerged friction stir processed passes were used in this study. All the specimens were extracted from three different joint positions (start, middle and end). The tests conducted included microstructural analysis, tensile tests, hardness and fracture surface morphology of the post-tensile specimens, were performed using a scanning electron microscope (SEM). There was no particular trend in the microstructure and mechanical properties when looking at the specimen positioning in all the passes. The minimum mean grain sizes were refined from 3.54 to 1.49 µm and the standard deviation from 5.43 to 1.87 µm. The ultimate tensile strength was improved from 84.96 to 94.77 MPa. The four-pass SFSPed specimens were found to have more ductile properties compared to the one-pass SFSPed one. The hardness of the stir zones in all the passes was found to be higher compared to the AA8011 base material but lower than the AA6082 one. The maximum stir zone hardness of 75 HV was observed on the one-pass SFSP joints.
... Whereas the hardness was found to have increased by 8.5% compared to that of the single-pass. Similar studies where the application of multi-pass FSP increased hardness were reported [61][62][63][64][65][66]. Surekha et al. [67] subjected the AA2219 alloy to multi-pass FSP and found that the hardness of the stir zone was lower compared to that of the base material. ...
Aluminium alloys have evolved as suitable materials for automotive and aircraft industries due to their reduced weight, excellent fatigue properties, high-strength to weight ratio, high workability/formability, and corrosion resistance. Recently, the joining of similar and dissimilar metals have achieved huge success in various sectors. The processing of soft metals like aluminium, copper, iron and nickel have been fabricated using friction stir processing. Friction stir processing (FSP) is a microstructural modifying technique that uses the same principles as the friction stir welding technique. In the majority of studies on FSP, the effect of process parameters on the microstructure was characterized after a single pass. However, multiple passes of FSP is another method to further modify the microstructure in aluminium castings. This study is aimed at reviewing the impact of multi-pass friction stir processed joints of aluminium alloys and to identify a knowledge gap. From the literature that is available on multi-pass FSP, it has been observed that the majority of the literature focused on the processing of plates than the joints. There is limited literature reporting on multi-pass friction stir processed joints. This then creates a need to study further on multi-pass friction stir processing on dissimilar aluminium alloys.
This study investigates the grain refinement process in Al2014 alloy through multi-pass friction stir processing (FSP) and its subsequent effects on microstructural evolution and mechanical characteristics. Optical microscopy and scanning electron microscopy were employed to study the microstructure, while mechanical characteristics were studied using a Vickers hardness tester and universal testing machine. The parent alloy showed a grain size of 98 µm, with a hardness of 147 HV, tensile strength of 456 MPa, and elongation of 17%. Through the FSP, grain size reduction was achieved with each pass, reaching 4.3 µm after the first pass, 3.9 µm after the second pass, and 4.7 µm after the third pass. Corresponding improvements in hardness, tensile strength, and elongation were observed. Hardness increased to 175 HV, 184 HV, and 171 HV after the first, second, and third passes, respectively. Tensile strength increased to 543 MPa, 559 MPa, and 532 MPa, while elongation improved to 31%, 33%, and 28% after each pass, respectively. Notably, the product of strength and elongation exhibited significant enhancements with each pass, indicating the effectiveness of the multi-pass FSP process in refining microstructures and enhancing mechanical properties.
In the present investigation, the effect of different tool geometry profiles, including triangular, square, hexagonal, and cylindrical pins, on the microstructure and mechanical characteristics of friction stir welded AA2014 alloys was studied. The friction stir welding resulted in the development of recrystallized fine grains in the nugget zone of the weld sample joined with different tool pin profiles. The microstructural investigation showed considerable differences in the grain size and distribution for various tool geometries within the weld nugget zone. In comparison to other pin profiles, triangular pin profiles showed finer and more uniform grain structures (4.7 microns). The welds made with triangular and square pins showed considerable changes in the weld zone architecture, including the appearance of more refined precipitates such as Al2Cu and Al2MgCu, and these results were supported by EDS analysis. Mechanical property analyses revealed that the tool geometry choice had a significant influence on the welds’ mechanical performance. Compared to hexagonal and cylindrical pins, triangular and square pin profiles have greater hardness values (122 HV) and better tensile strength (359 MPa). Additionally, it was discovered through a fracture behavior analysis that welds made with square and triangular pins had more ductile fracture characteristics, but welds made with hexagonal and cylindrical pins had a comparatively brittle fracture behavior.
The current investigation focuses on the effect of cooling technology on the corrosion behavior of friction stir processing (FSP) of AA5083 alloy. After processing, the equiaxed refined grains were created in all the specimens, and the specimen processed in water led to more grain refinement than other specimens. Three types of intermetallics (IMs), such as iron-based needle IMs, Mg-based round IMs, and small Mg-based IMs at grain boundaries, were identified in both base metal and FSPed specimens. After FSP, these IMs fragmented into small particles and dispersed homogeneously in the aluminum matrix. Moreover, the heat generated between the work and tool junction caused the coarsening, reformation, and dissolution of IMs based on the availability of heat input. Four types of corrosion tests were carried out: immersion test, open circuit potential test, Tafel polarization test, and electrical impedance spectroscopy test to analyze the electrochemical behavior of FSPed specimens. All the corrosion findings stated that the corrosion resistance improved after the processing due to the formation of uniform grain structure, less density of iron-based IMs, and discontinuous IMs. Within FSPed specimens, the specimen processed in water led to greater corrosion resistance than other specimens owing to better grain refinement and small IMs.
The friction stir welded dissimilar aluminium alloy joints AA8011-AA6082 were subjected to multiple-pass friction stir processing under different operating conditions. The processing conditions used included room temperature (normal) and underwater (submerged) friction stir processing. Microstructural analysis, hardness and tensile tests were conducted to analyze the impact of different multiple-pass friction stir processing conditions on the friction stir welded dissimilar aluminium alloy joints. The microstructural results showed that the multiple-pass submerged friction stir processed grain structure was 67.72% finer compare to those of the multiple-pass normal friction stir processed joints. The ultimate tensile strength obtained correlated the grain size behaviour resulting in the multiple-pass submerged joint having a UTS with a 3.2% increase in comparison to that of the normal friction stir processed joints. The percentage elongation results correlated with the tensile and grain size results. The multiple-pass submerged friction stir processed joints had a maximum hardness of 65 HV and the normal multiple-pass friction stir processed joints had a hardness of 53 HV.
