The elimination of the FexAly type phases was considered the solution to low ductility presented in aluminum-steel welded joints. Recently, the researches do not seek the suppression but the control of the thickness of these compounds. In this work, Al-Fe joints were manufactured by solid state and fusion welding, looking for controlling the formation of intermetallic compounds. Temperature measurements were carried out during the welding. The joints interface was characterized using optical and scanning electronic microscopy, aided by chemical composition measures with X-EDS. The microstructural characterization at the interface of aluminum-steel joints, in solid state welded joints, demonstrated the absence of intermetallic compounds, which is attributed to the low temperature reached during the process-less than 300 ° C. In the case of fusion joints, it has observed the permanent formation of intermetallic compounds whose thickness varies significantly with the heat input.

In this paper, thermo-mechanical behavior of the welding process was analyzed to determine the effect of edge preparation on the residual stress magnitude and distribution in Dissimilar joints. By using a verified finite element model, an efficient user subroutine was developed to consider the effects of phase transformation. In order to verify the model, experimental data for similar and Dissimilar joints, obtained by deep hole drilling method, were utilized. Good agreement was observed between the finite element and experimental data. The results indicated that the developed computational method is an effective tool to predict the residual stress of Dissimilar weld joints. The present finite element model was developed in a butt-welded pipe to consider the effect of pipe wall-thickness, groove shape and root opening distance. It was observed that the pipe wall-thickness has important influences on the distribution and magnitude of residual stress. Moreover, By increasing the pipe thickness in the Dissimilar butt-welded pipes, tensile axial residual stresses on the inner surface of the Dissimilar joint decreased on the stainless steel side, but only a small variation was observed on the carbon steel side.The compressive axial residual stresses on the inner surface and the tensile axial residual stresses on the outer surface increased by increasing the pipe wall thickness, especially on the carbon steel side.Increasing the weld groove shape and root opening distance leads to higher compressive axial stresses on the inner surface and higher tensile axial stresses on the outer surface, only on the carbon steel side.

In this research, microstructure and mechanical performance of Dissimilar resistance spot welded DP780/DP980 dual-phase steels were studied utilizing optical microscope, microhardness, and tensile shear tests. Resistance spot welding (RSW) was performed in the current range of 7 to 12 kA, with 0. 5 kA steps. At welding currents lower than 7 kA low amount of melting led to the very low strength of the joints due to small weld nugget diameter. The results showed that an increase in welding current from 7 kA up to 11 kA, result in an increase in weld nugget diameter. Further increase of welding current (higher than 11 kA), however decreased the weld nugget diameter due to severe melt expulsion. Microstructural studies showed that weld nugget was primarily comprised of martensite, and the heat-affected zone (HAZ) of both sides of the joint was comprised of three different microstructural zones; upper-critical HAZ (UCHAZ), inter-critical HAZ (ICHAZ), and sub-critical HAZ(SCHAZ). Microhardness test showed that at both sides, softening occurred at SCHAZ. The results of the tensile shear test showed that both peak load and fracture energy of the joints followed approximately the same trend as weld diameter with welding current. Two different fracture modes of interfacial failure (IF) and pullout failure (PF) were observed in the tensile-shear test. At welding currents lower than 10 kA, the failure occurred in IF mode, while at higher welding currents, PF was dominant. Weld nugget diameter at welding current of 10 kA; i. e., critical weld nugget diameter, was ~8. 5 mm.

The relatively new solid state welding process friction stir welding (FSW) was applied in this research work to join similar and Dissimilar aluminum alloys AA5754-H22 and AA6063-T4. Different welding rotational speed and transverse speed applied. The joint which was fabricated using tool rotational speed of 2000 rpm and transverse speed of 4 mm/min yielded the best mechanical properties. Soundness of joint was proved by non-destructive tests such as visual inspection and radiography. The global mechanical behavior of the similar welds is very similar to that of the base material. For Dissimilar weld important losses in ductility was reported. Microstructural evaluation of fractured surface showed that ductile fracture was the major fracture mechanism of similar and Dissimilar welds.

In this study, friction stir butt welding of Mg and Al alloys with applying Zn interlayer was performed. To obtain optimum condition, a combination of two travel and three rotation speeds were selected. Mg-Zn and Mg-Al-Zn IMCs, Al solid solution and residual Zn, were the most common phases in the stirred zone, which eliminated the formation of Al-Mg intermetallics. The maximum mechanical properties were achieved for the joint fabricated at 35 mm/min and 600 rpm, caused to 24% improvement in tensile strength and around 3 times enhancement of elongation compared with Zn free sample FSWed at the same conditions. The fracture micrographs were consistent with corresponding ductility results. Fracture surfaces of Zn-added samples presenteda fine texture with a mixture of brittle and ductile fracture feature, which was different from the coarse cleavage plane and fully brittle fracture of the joint without Zn interlayer.

Dissimilar welded joints of AISI 430 and AISI 316L stainless steel were produced by the GMAW process using two different shielding gas mixtures composed of 97Ar-3N2 and 80Ar-19He-1O2. The microstructure of the heat-affected zone was characterized by optical and scanning electron microscopy, and Vickers microhardness measurements were carried out along the cross-section of the specimens. The Dissimilar welded joints were submitted to immersion corrosion test in a 10%v/v hydrochloric acid solution for 24 and 72 hours. Afterward, yields strength, tensile strength, and elongation percentage were measured using tensile tests according to ASTM E8 standard. Non-immersed welded joints were used for comparison purposes. An analysis of variance was developed to evaluate the influence of immersion time and shielding gas mixture on yielding strength and tensile strength. The microstructure characterization showed that the heat-affected zone on AISI 430 side was the widest, and it was observed a significant presence of acicular ferrite, martensite, and coarsened ferritic grains. In contrast, on the heat-affected zone on AISI 316L side was not observed coarsening nor refinement of austenite grains. The AISI 430 heat-affected zone showed the maximum hardness values and higher susceptibility to corrosion damage. Tensile tests results evidenced that immersion corrosion tests did not change significantly ultimate strength in comparison to non-immersed specimens while yielding strength and elongation percentage were drastically decreased due to immersion time. According to the p-value, the immersion time is the most influencing factor on yielding strength and tensile strength of the Dissimilar welded joints.

In this study, friction stir welding (FSW) was used for joining AL-1100 to AZ31. In the rotation speed between 400 to 800rpm and travel speed between 15 to 30mm/min, in the condition that stirring pin was inserted in Mg side of weld, friction stir welded samples without any defect were made. In high rotation speed, intermetallic compounds were seen in the XRD results of the stir zone. The best tensile strength, about 122MPa, was reached in rotation speed of 570rpm and travel speed of 20mm/min.

In the present study, to resolve the problems in fusion welding methods as well as to increase the strength, FSW method was used to join aluminum alloy sheets 6061 and 2024. Moreover, optimal parameters for joining of these two alloys were also taken into consideration. Various tool rotation speeds of 565, 950 and 1500 rpm were selected. For each tool rotation speed, two traverse speed variables, two penetration depth variables, and two tool angle variables were specified. The analysis of mechanical properties of welded samples was conducted through tensile and micro-hardness tests. Furthermore, microstructure of welding zone was investigated using optical and electron microscopes. The ratio of shoulder diameter to pin diameter is among the most significant and practical factors for welding tools. So, a shoulder diameter three times larger than that of pin diameter was selected. In the present study, alloy 2024 was placed at the precursor as the harder alloy. Tensile strength and indentation hardness of optimal specimen 300 MPa and 85 HV were achieved. Moreover, hardness behavior and tensile strength of heat-affected zone (HAZ) was evaluated to be lower in alloy 6061 compared to other zones.

The aim of the present study is to investigate the effect of Al-Fe intermetallic compounds on the strength of friction stir spot welded (FSSW) joints. The tool rotational speed and dwell time were the studied process parameters. The microstructure of the joint interface was characterized using optical and scanning electron microscopes. Tensile-shear testing results showed that the strength of the welds improved with the enhancement of dwell time for all of the applied rotational speeds. Furthermore, for a given dwell time, higher rotational speeds led to stronger joints. Microstructural observations revealed that the strength of the welds increased with the growth of the intermetallic layer thickness up to 5 mm.