Thermo-mechanically Affected Zone Research Articles

Microstructure analysis of pressure resistance seal welding joint of zirconium alloy tube-plug structure

Pressure resistance welding is usually used to seal the connection between the cladding tube and the end plug made of zirconium alloy. The seal welded joint has a direct effect on the service performance of the fuel rod cladding structure. In this paper, the pressure resistance welded joints of zirconium alloy tube-plug structure were obtained by thermal-mechanical simulation experiments. The microstructure and microhardness of the joints were both analyzed. The effect of processing parameters on the microstructure was studied in detail. The results showed that there was no β-Zr phase observed in the joint, and no obvious element segregation. There were different types of Widmanstätten structure in the thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ) of the cladding tube and the end plug joint because of the low cooling rate. Some part of the grains in the joint grew up due to overheating. Its size was about 2.8 times that of the base metal grains. Due to the high dislocation density and texture evolution, the microhardnesses of TMAZ and HAZ were both significantly higher than that of the base metal, and the microhardness of the TMAZ was the highest. With the increasing of welding temperature, the proportion of recrystallization in TMAZ decreased, which was caused by the increasing of strain rate and dislocation annihilation.

Structure–Property Correlation between Friction-Welded Work and Hardened Al-4.9Mg Alloy Joints

Friction welding of aluminum alloys holds immense potential for replacing riveted joints in the structural sections of the aeronautical and automotive sectors. This research aims to investigate the effects on the microstructural and mechanical properties when AA5083 H116 joints are subjected to rotary friction welding. To evaluate the quality of the welds, optical and scanning electron microanalysis techniques were utilized, revealing the formation of sound welds without porosity. The microstructural examination revealed distinct weld zones within the weldment, including the dynamically recrystallized zone (DRZ), thermo-mechanically affected zone (TMAZ), heat-affected zone (HAZ), and base metal (BM). During the friction-welding process, grain refinement occurred, leading to the development of fine equiaxed grains in the DRZ/weld zone. Tensile testing revealed that the weldment exhibited higher strength (YS: 301 ± 6 MPa; UTS: 425 ± 7 MPa) in the BM region compared to the base metal (YS: 207 ± 5 MPa; UTS: 385 ± 9 MPa). However, the weldment demonstrated slightly lower elongation (%El: 13 ± 2) compared to the base metal (%El: 15 ± 3). The decrease in ductility observed in the weldment can be attributed to the presence of distinct weld zones within the welded sample. Also, the tensile graph of the BM showed serrations throughout the curve, which is a characteristic phenomenon known as the Portevin–Le Chatelier effect (serrated yielding) in Al-Mg alloys. This effect occurs due to the influence of dynamic strain aging on the material’s macroscopic plastic deformation. Fractography analysis showcased a wide range of dimple sizes, indicating a ductile fracture mode in the weldment. These findings contribute to understanding the microstructural and mechanical behavior of AA5083 H116 joints subjected to rotary friction welding.

Microstructure and Mechanical Properties of Friction Stir Welded DP1180 Steel Plates

The effect of rotation speeds from 100 to 600 rpm on the microstructure and mechanical properties of friction stir welded (FSW) DP1180 steel joints was studied. The microstructure in the different weld zones were examined using optical microscopy (OM), scanning electron microscopy (SEM), electron backscattering diffraction (EBSD), and transmission electron microscope (TEM). It was found that when welded at 100 rpm, there was an obvious boundary formed in the middle of the stir zone (SZ), which divided the SZ into two parts, namely, SZ-Ⅰ and SZ-Ⅱ. Significantly refined microstructures with an average grain size of 0.41 μm and 0.28 μm were observed in SZ-Ⅰ and SZ-Ⅱ, respectively. The SZs were mainly composed of martensite when the rotation speed increased over 200 rpm. The thermo-mechanically affected zone (TMAZ) of all joints was composed of martensite and ferrite. Microhardness tests showed that the minimum microhardness of heat affected zone (HAZ) of all joints was between 280–300 HV. It was revealed that as the rotation speed increased, the tensile strength of the joint decreased. The tensile strength of the 100 rpm joint was the highest, reaching 1094 MPa. The fracture position of the 100 rpm joint was in SZ while the fracture positions of the other joints were in HAZ.

Microstructure evolution and mechanical properties of friction stir welded joint of ultrafine-grained dissimilar AA2024/AA5083 composite fabricated by accumulative roll bonding

In this investigation, the dissimilar ultrafine-grained (UFG) composite of AA2024 and AA5083 was made using four cycles of accumulative roll bonding (ARB). The composite was then welded by the friction stir welding (FSW) method. Using the Taguchi technique, welding parameters of tool rotational speed, welding speed, pin geometry, and tool tilt angle were optimized. Optical microscopy, Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) were used to study microstructural evolution in the ARB processed specimen, as well as in the stir zone (SZ), thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ). Taguchi optimization showed that a Square pin, with a rotational speed of 655 rpm, welding speed of 110 mm/min, and tool tilt angle of 3° were the optimum welding process parameters. The microstructural assessment showed that the SZ consisted of a recrystallized microstructure with an average grain size of about 900 nm. Tensile strength was reduced from 667 MPa in the ARB-processed sample to 403 MPa in the optimized FSW condition. However, yield strength was slightly reduced due to the ultrafine-grains of the weldment. The relatively high strength of the composite was due to solid solution, grain boundaries strengthening, and nano-sized Al20Cu2Mn3 precipitates (T-phase) formation. The presence of precipitates led to a proper level of ductility of up to two times in the FSW structure compared to the UFG structure. The highest mean hardness of the weldment, ∼132 HV, was obtained which was due to the grain refinement, dislocation generated by the pin movement, and small-size precipitates.

Metallurgical investigation of direct drive friction welded joint for austenitic stainless steel (AISI 316)

The present study investigates the metallurgical behavior of direct-drive friction-welded (DDFW) joints for high Cr, Ni, and Mo steel (AISI 316). Macro-microscopic, microhardness, and X-ray diffraction (XRD) were conducted. The results for the macroscopic view showed that the narrow welding center did not exceed 600 µm and there were no macro cracks or defects, indicating a uniform structure. The microstructure exhibited a significant welded joint interface with microcavities and a grain refinement of 10 µm, about three times smaller than the grain size of AISI 316, due to the creation of a highly plastically deformed zone (HPDZ), while the thermo-mechanically affected zone (TMAZ) formed in the neighboring area with a grain growth of about 100 µm, relatively enlarged three times compared to AISI 316 and time time related HPDZ. Thus, the high level of microhardness was investigated at the welding center and low values in the neighboring area were caused by the formation of the HPDZ and TMAZ, respectively. XRD also illustrated the concentration of gamma iron at the 111 level due to the grain refinement resulting from high plastic deformation.

Influence of tool pin shape and rotation speed for friction stir spot welding of AZ91 magnesium alloy sheets

Abstract Light weight design is believed one of the most effective ways to enhance performance, reduce fuel consumption and harmful gases for air and land vehicles. Hence, welding lightweight metals like magnesium alloys is very important. Friction stir spot welding joints of 2 mm thick AZ91 magnesium alloy sheets by overlapping two of them were performed utilizing two welding tools having conical and triangular pin at 800, 1200 and 1600 revolution per minute (rpm) tool rotational velocities for each tool to identify the pin shape and rotation speed impact on microstructure and mechanical features of the created joints. The stir zones of the joints contained smaller grains, therefore had higher hardness in comparison to AZ91 base metal, thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ). The lowest hardness values were found in HAZ of the welds. Hardness fell slightly with a rise in rotation speed for both tools because of more heat input. Strength of the joints manufactured applying the triangular pin tool was better because this pin mixed materials better, thus created joints with bigger welding area and greater hardness. The strongest weld was fabricated by applying triangular pin tool and 1600 rpm.

Evolution of Microstructures, Texture and Mechanical Properties of Al-Mg-Si-Cu Alloy under Different Welding Speeds during Friction Stir Welding

The effects of different welding speeds on the microstructures and mechanical properties of Al-0.75Mg-0.75Si-0.8Cu alloys were investigated using optical metallographic microscopy (OM), X-ray diffraction (XRD) analysis, an ETM105D electronic universal testing machine and field emission electron microscopy (SEM). The results reveal that during the friction stir welding process, the welded joint forms the base material (BM), heat-affected zone (HAZ), thermomechanically affected zone (TMAZ) and nugget zone (NZ), under the action of shear force and friction heat. The textures present in the BM are mainly C ({001}<100>) recrystallised cubic texture and P({110}<112>) recrystallised texture, Goss (G) texture, brass (B) texture and {112}<110> rotating copper texture. The organisation of the NZ undergoes dynamic recrystallisation, forming fine isometric crystals with large angular grain boundaries, accounting for more than 75% of the total. The geometrically necessary dislocations (GNDs) in the NZ grow as the welding speed rises. Moreover, {111}<11−0> and {111}<1−10> shearing textures, {001}<110> recrystallisation textures and fibre textures are mainly present in NZs. The average grain size in the NZ was the smallest, and the mechanical properties were the best at a welding speed of 125 mm/min. The grain size and the tensile strength and elongation of the NZ were 2.945 µm, 200.7 MPa and 12.7% for the joint at a welding speed of 125 mm/min, respectively.

Heterogeneous microstructure improves the strength and ductility of a flash-butt welded IN718 alloy joint

Higher strength and ductility are obtained in a flash-butt welded IN718 alloy joint due to an improved heterogeneous microstructure distribution by adjusting the upsetting deformation. With the increase in upsetting deformation, the microstructure distribution of the characteristic zones is effectively adjusted which contains a complete recrystallization zone (RxZ), a thermo-mechanical affected zone (TMAZ) and a coarse grain zone (CGZ). Finer grains and more residual stress are obtained in the heat affected zone (HAZ), which increases the strength and hardness. The improvement of the strength in the HAZ delays the concentration rate of local strain at the weld seam (WS) and enhances the coordination between the HAZ and the matrix. Therefore, the additional ductility is obtained by the coordination between the HAZ and the matrix, which results in a welded sample of UD0.86 achieving the same high strength and ductility as that of the base material.

Effect of welding speeds on the metallurgical and mechanical property characterization of friction stir welding between dissimilar aerospace grade 7050 T7651-2014A T6 aluminium alloys

Friction stir welding (FSW) is an effective technique for producing quality welds and resolving solidification issues of aluminium alloys found in fusion welding (FW) techniques. This study seeks to establish the effect of welding speeds (WSs) of 25, 45, 65, and 85 mm/min with a constant tool rotation speed (TRS) of 1000 rpm and a tool tilt angle (TTA) of 20. Furthermore, mechanical testing was performed to determine the tensile strength, microhardness, and residual stresses. In addition, microstructure characterization was performed using optical microscopy, SEM/EDS and EBSD to identify the quality assurance of the dissimilar AA7050 T7651-AA2014A T6 weld joint. The results indicated that while the WS increased from 25 to 85 mm/min, the width of the stir zone decreased from 9.497 mm to 6.315 mm, according to the macrostructure analysis. Moreover, microstructural analysis reveals the direction of material flow and grain structure on the advancing side (AS) and retreating side (RS) of the thermo-mechanical affected zone (TMAZ) in the weldment. EBSD analysis reveals the 65 mm/min weld joint has a finer grain size (the average grain size is 2 µm) compared to other WS. Residual stress analysis also reveals compressive residual stress in all weld zones except for RS. The RS of residual stress values for 25–85 mm/min weld joints is 3, 7, 4, and 5 MPa. At the same time, UTS values were obtained as 274 MPa (25 mm/min), 317 MPa (45 mm/min), 332 MPa (65 mm/min), and 308 MPa (85 mm/min), and fracture occurred on the RS of all the welded joints, which was confirmed by harness values that are (AS and RS) 115–157 HV and 63–154 HV, respectively. The observed results show that WS at 65 mm/min has better mechanical and metallurgical properties than other welding speeds because of proper material mixing and finer grains obtained in the weldment, which resulted in higher UTS values being attained for WS at 65 mm/min of the FSW joint.

Prediction of Tool Eccentricity Effects on the Mechanical Properties of Friction Stir Welded AA5754-H24 Aluminum Alloy Using ANN Model.

The current study uses three different pin eccentricities (e) and six different welding speeds to investigate the impact of pin eccentricity on friction stir welding (FSW) of AA5754-H24. To simulate and forecast the impact of (e) and welding speed on the mechanical properties of friction stir welded joints for (FSWed) AA5754-H24, an artificial neural network (ANN) model was developed. The input parameters for the model in this work are welding speed (WS) and tool pin eccentricity (e). The outputs of the developed ANN model include the mechanical properties of FSW AA5754-H24 (ultimate tensile strength, elongation, hardness of the thermomechanically affected zone (TMAZ), and hardness of the weld nugget zone (NG)). The ANN model yielded a satisfactory performance. The model has been used to predict the mechanical properties of the FSW AA5754 aluminum alloy as a function of TPE and WS with excellent reliability. Experimentally, the tensile strength is increased by increasing both the (e) and the speed, which was already captured from the ANN predictions. The R2 values are higher than 0.97 for all the predictions, reflecting the output quality.

The Microstructure Evolution and Mechanical Properties of Rotary Friction Welded Duplex Stainless Steel Pipe.

The use of duplex stainless steel (DSS) in various fields is promising due to its excellent anti-corrosion properties, but traditional welding can lead to the formation of unfavorable phases that deteriorate its quality. This study aimed to use the rotary friction weld (RFW) technique to prevent the formation of harmful phases in the welding of an S32205 alloy pipe. The welding parameters used included a rotating speed of 20 m/s, a friction pressure of 10 MPa, a friction time of 30 s, and a forging pressure of 30 MPa. The microstructure and mechanical properties of the resulting RFWed joint were investigated. The results revealed that the weld zone exhibited a microstructure consisting of ferrite and austenite phases, with no deleterious phase detected. The ferrite content was measured to be 53.3%, 54.5%, and 68.7% in the base metal, thermomechanical affected zone (TMAZ), and weld, respectively, owing to the rapid cooling rate in the RFW process, which prevented any harmful phase formation in the weld zone. Furthermore, the RFW process successfully produced an ultrafine grain with a ferrite/austenite grain size of 0.40 μm and 0.41 μm, respectively. The weld zone and TMAZ contained more low-angle grain boundaries (LAGBs) compared to the base metal, which was attributed to the dynamic recovery (DRV) within a grain. The high heating and cooling rates and short welding time of the RFW process did not allow sufficient time for the dynamic recrystallization of the microstructure in the weld zone. However, a slight increase in the ferrite content in the weld zone resulted in grain refinement and an increase in the dislocation density, resulting in a slight increase in the 358 HV0.2 hardness and 823 MPa tensile strength of the weld zone. This study offers a novel approach for obtaining ultrafine grain duplex stainless steel pipes with exceptional mechanical properties through the application of RFW.

Correlation between local mechanical properties and corresponding microstructures in a friction stir processed Monel alloy

Friction stir processing (FSP), an innovative local microstructural modification technique for bulk material, has been used to process Monel alloy. A detailed microstructural analysis was conducted by acquiring high-resolution electron backscatter diffraction (EBSD). The local tensile properties and hardness nanoindentation were obtained for the different FSP area zones. The coarse equiaxed grain structure of 18.9 μm average grain size at the base material (BM) has been dynamically recrystallized refined equiaxed grains of an average grain size of 3.6 μm in the stir zone (SZ) where the thermomechanically affected zone (TMAZ) has an average grain size of 10.7 μm. The grain structure at the interface of the SZ and TMAZ consisted of mixed fine recrystallized grains and coarse deformed grains. The SZ is dominated by significantly refined grains, with the highest fraction of high-angle grain boundaries (HAGBs) of about 71%. The point-to-point misorientation measured by Kernel Average Misorientation (KAM) indicates low values in the SZ compared with the highest values at the interface between SZ and TMAZ. In terms of tensile properties, the yield strength of TMAZ and SZ improved to 380 and 440 MPa, respectively. The ultimate tensile strength (UTS) also increased by 18% from 499 to 593 MPa in TMAZ and 37% from 499 to 699 MPa in the SZ. The maximum nano hardness found in the TMAZ of about 7.13 ± 1.92 GPa due to the high density of the substructure. However, the SZ slightly increased to 3.88 ± 0.22 GPa from 3.33 ± 0.17 GPa of the BM.

Microstructure and crystallographic texture of high frequency electric resistance welded X65 pipeline steel

Microstructure and crystallographic texture and their correlation with impact toughness of high-frequency electric resistance welded (HF-ERW) X65 Grade pipeline steel have been investigated. X65 base metal after HF-ERW has formed a typical hourglass-shaped weld joint with four different regions, including the thermomechanical-affected zone (TMAZ), fine-grained heat affected zone (FGHAZ), coarse-grained heat affected zone (CGHAZ), and bondline (Weld Zone). X65 base metal shows prominent (113) [110] and (112) [110] texture components due to thermomechanical-controlled processing. TMAZ depicted random texture with a minor intensity of Cube component (001)[110] due to the partial recrystallization during welding. In the FGHAZ and CGHAZ, near the bondline, the base metal texture has been converted to rotated Goss (110) [110], Goss (110) [001], and rotated cube (001) [110] due to the recrystallization of the austenite and the shear deformation in the austenite temperature range. A high density of {100} and {110} cleavage planes is observed in the CGHAZ, which is often found to be the fracture location for the impact toughness testing.

Influence of Microstructure and Mechanical Properties of Dissimilar Rotary Friction Welded Inconel to Stainless Steel Joints.

The present study aims to evaluate the microstructure, grain size, and mechanical properties of the dissimilar AISI 316L/Inconel 718 (IN 718) rotary friction welded joints under both the as-welded and post-weld heat treatment (PWHT) conditions. Because of reduced flow strength at elevated temperatures, the AISI 316L and IN 718 dissimilar weldments exhibited more flash formation on the AISI 316L side. At higher rotating speeds during friction welding, an intermixing zone was created at the weld joint interface due to the material softening and squeezing. The dissimilar welds exhibited distinctive regions, including the fully deformed zone (FDZ), heat-affected zone (HAZ), thermo-mechanically affected zone (TMAZ), and the base metal (BM), located on either side of the weld interface. The dissimilar friction welds, AISI 316L/IN 718 ST and AISI 316L/IN 718 STA, exhibited yield strength (YS) of 634 ± 9 MPa and 602 ± 3 MPa, ultimate tensile strength (UTS) of 728 ± 7 MPa and 697± 2 MPa, and % elongation (% El) of 14 ± 1.5 and 17 ± 0.9, respectively. Among the welded samples, PWHT samples exhibited high strength (YS = 730 ± 2 MPa, UTS = 828 ± 5 MPa, % El = 9 ± 1.2), and this may be attributed to the formation of precipitates. Dissimilar PWHT friction weld samples resulted in the highest hardness among all the conditions in the FDZ due to the formation of precipitates. On the AISI 316L side, prolonged exposure to high temperatures during PWHT resulted in grain growth and decreased hardness. During the tensile test at ambient temperature, both the as-welded and PWHT friction weld joints failed in the HAZ regions of the AISI 316L side.

Multi-scale characterizations of microstructure and mechanical properties of Ti6242 alloy linear friction welded joint with post-welded heat treatment

A near α titanium alloy (Ti6242) was joined by the linear friction welding technique followed by the post- welded heat treatment (PWHT). Both joints in as-welded and PWHTed conditions were characterized in a multi-scale manner to investigate the evolution of microstructure and establish the relationship between the microstructure and mechanical properties of the joints. Results show that both joints fail in the base material, while the PWHTed joints have large hardness enhancement in the welding line (WL) and thermo-mechanically affected zone (TMAZ). After heat treatment, the cluster of the flakier α phase is formed inside the equiaxed grains in WL, while the martensite phase in TMAZ is decomposed into the (α+β) phase, both of which can improve the hardness of the joint.

The influence of tool rotational speed on microstructure and mechanical performance of dissimilar FSLW

FSLW is a novel solid-sate joining process in aircraft assembly technology that has offered superior welding quality to the joining of aluminum alloy. Concerning the success of FSLW light metal alloys coupled with lower operating costs due to improved energy efficiency and virtual lack of a consumable has emphasized the need to examine AA 2024-T4 and AA 7075-T6 based on different tool rotational speeds (RSs). This research examined the three important determinants of FSLW: cross-section morphology, microstructure behavior, and mechanical performance (lap shear failure load and fracture location) to realize the quality and reasonable experiment of the welding technique. The cross-section of the lap joint is investigated in this experiment; it is evident that the maximum temperature is found in the stir zone, and the shape looks like a bowl type. Further, it is found that tool RS does not have an influence on the effective sheet thickness, but it influences the effective lap width. With the increased RS, the effective lap width increased first and then decreased. Concerning grain size analysis, the bigger grain size was observed in the heat-affected zone, and the smaller grain size was observed in the thermomechanical-affected zone. According to the mechanical performance analysis, the lap shear failure load increased and then reduced with increased RS.

Local Microstructure and Texture Development during Friction Stir Spot of 5182 Aluminum Alloy

The local microstructure, texture gradient and mechanical properties through the shoulder dimension (10 mm) of upper and lower AA5182 aluminum sheets were investigated using electron backscatter diffraction (EBSD) and Vickers microhardness after friction stir spot welding (FSSW). Based on the microstructural features (mean grain size, grain boundary type and dynamic recrystallization (DRX)), the upper sheet was found to be mainly composed of the stir zone (SZ) and thermomechanically affected zone (TMAZ) due to the high deformation induced simultaneously by the tool rotation and the shoulder download force, while the SZ, TMAZ, heat-affected zone (HAZ) and base metal (BM) were detected in the lower sheet due to the limited effect of the shoulder on the lower sheet. The texture changes, due to the nature of the deformation, demonstrated a shear-type texture at the SZ to a plane strain compression deformation type texture at the TMAZ and then a recrystallization texture at the HAZ and BM. The microhardness gradually decreased with the increasing distance from the keyhole along the SZ, TMAZ and HAZ regions. Eventually, the microstructure and microhardness evolutions were correlated based on the Hall–Petch relationship.

Effect of Heat Treatment on the Microstructure and Mechanical Properties of Rotary Friction Welded AA7075 and AA5083 Dissimilar Joint

The present work aims to investigate the changes in the microstructural and mechanical properties of various pre- and post weld heat treatments (PWHTs) on rotary friction welded dissimilar (AA7075 and AA5083) aluminum alloys. The investigation focused on the evolution of weld macro- and microstructures, as well as the changes in hardness and tensile properties resulting from friction welding. The joint integrity was studied through various characterization techniques, and no cracks or incomplete bonding was observed. The study found that the dissimilar joints of the AA7075 and AA5083 alloys displayed higher flash formation on the AA7075 side, which has a lower melting temperature compared to the AA5083 alloy. Various zones were identified in the weld region, including the dynamic recrystallized zone (DRZ), the thermomechanically affected zone (TMAZ) consisting of TMAZ-1 (elongated grains) and TMAZ-2 (compressed/distorted grains), the heat-affected zone (HAZ), and the base metal (BM) zone. The rotary friction welded sample AA5083/AA7075-PWHT joint exhibited the highest strength (yield strength (YS): 195 ± 3 MPa, ultimate tensile strength (UTS): 387 ± 2 MPa) among all the other welded conditions, and this may be attributed to the major strengthening precipitates MgZn2 (of AA7075) formed during postweld aging. All dissimilar welds failed in the HAZ region of the AA5083 side due to the formation of coarse grains, indicating the weakest region.

Rotary friction welding of Inconel 718 – AISI 304 stainless steel dissimilar joint

Nickel-based superalloy Inconel 718 and austenitic stainless steel AISI 304 are joined by rotary friction welding. The changes in microstructure and mechanical properties of the dissimilar joint for solutionising, solutionising + aging, and post-weld aging treatment, with a prior solution heat treatment, are studied. Two distinct microstructural zones, the FDZ (fully deformed zone) and the TMAZ (thermo-mechanically affected zone) are observed in all weldments. The post-weld aged joint sample shows the highest tensile strength and hardness due to the precipitation of γ′ (Ni3(Ti, Al)) and γ″ (Ni3Nb) strengthening precipitates. The solution-treated sample shows the highest yield strength, while the solutionising + aging treatment is found to deteriorate the mechanical properties of the dissimilar joint. The observed changes in the mechanical properties are investigated based on microstructure and electron dispersive spectroscopy.

Effect of Heat Treatment on the Microstructure and Mechanical Properties of Rotary Friction Welded Dissimilar IN718 to SS304L Alloys

The present study investigated the effect of heat treatment (pre- and post-weld) on the microstructure and mechanical properties of an SS304L/IN718 dissimilar rotary friction welded alloy. Optical and scanning electron micrographs of the dissimilar rotary friction welded SS304L/IN718 joints in solution-treated (ST), solution-treated and aged (STA), and post-weld heat treatment (PWHT) conditions revealed defect-free welds. Furthermore, various zones were observed across the weld region, namely the fully deformed zone (FDZ), thermomechanical affected zone (TMAZ), heat affected zone (HAZ), and base material (BM). Among the SS304L/IN718 dissimilar friction welds with different heat treatment conditions (prior ST and STA, PWHT), the PWHTed dissimilar welds exhibited excellent mechanical properties, which could be attributed to the formation of the strengthening precipitates γ′ and γ″ during double aging in PWHT. In contrast, the mechanical properties were found to be the poorest in the STA condition, possibly due to the dissolution of the strengthening precipitates γ′ and γ″ during friction welding. It was observed that the SS304L/IN718 dissimilar friction welds in the ST and STA conditions failed in the HAZ of the SS304L side, away from the weld interface, indicating that the weld region was stronger than the weakest base metal (SS304L) in the various joints.