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In this study, we explored the impact of intercritical tempering on the microstructural evolution and mechanical properties of dissimilar welds formed through laser welding between 5%Ni steel (SA645) and austenitic stainless steel (AISI304L). Upon tempering at 500 °C, reversed austenite manifested within the weld metal. The volume proportion of reversed austenite in weld metal at room temperature increased first, exhibiting a maximum (∼10%) at ∼600 °C, and then decreased with increasing tempering temperature, which was associated with the diminished stability of austenite. Due to the change in tempering temperatures, two distinct types of reversed austenite were present, with one being located at the high-angle grain boundaries and the other within the martensite blocks. As the tempering temperature increased, the weld metal hardness decreased, reaching a minimum of ∼306 HV at 600 °C, and then increased. The dislocation density within the martensite matrix and the quantity of reversed austenite are the crucial factors to determine the hardness of weld metal. The cryogenic impact toughness of weld metal increased at first and then decreased as the tempering temperature increased. The maximum of ∼40 J for the cryogenic impact toughness was obtained when tempering at 600 °C. The low-temperature impact toughness of the weld metal was determined by the synergy of the TRIP effect of reversed austenite, the compatible deformation capability of dual-phase structure, and the crack propagation behavior.

Dissimilar metal welded joints are increasingly and widely applied in any field of manufacturing. Meanwhile, a novel keyhole gas tungsten arc (K-TIG) welding technology presents the advantages of high productivity, high precision as well as low cost. This paper investigated microstructural characterization of K-TIG welded SAF2205/Q235 dissimilar joints with different welding torch deviations. Moreover, evolution of local microstructure and stress–strain behavior from transition zone was discussed by means of crystal plasticity finite element modeling. The results show that solid–solid phase transformation mode in the weld metal changes due to the change of constituent alloy elements. Noted that transition zone on the Q235 side includes compact martensite with high hardness, and the elements and mechanical properties present a severe gradient distribution. Transition zone with high strength has a greater resistance to plastic deformation. In addition, a large strain gradient takes place near the transition zone and on the side of an austenite grain with a high Schmid factor. Besides, the twin boundary is prone to deform at a lower stress level, which leads to a new strain partition. Therefore, stress–strain incompatibility caused by a difference in both mechanical properties and crystal structure is the root cause of K-TIG DMWJs failure.

The transportation industry has played a crucial role in advancing human society, but it has also raised concerns about carbon emissions and environmental pollution. As a result, significant research is being conducted in various areas, such as electric vehicles, powertrain energy efficiency, shared mobility, and autonomous driving. However, vehicles remain essential, and reducing their energy consumption is vital. One effective way to achieve this is by light–weighting vehicle materials. In the past, steel was the primary material used, but the transition to materials like aluminum has shown better weight-to-strength ratios. To drive change, we must explore the use of diverse materials since no single material is perfect. By combining specific materials, we can complement their weaknesses and enhance their strengths, opening up new possibilities for the future of mobility. One critical factor in advancing future mobility is the joining of dissimilar materials. This paper delves into various methods of joining dissimilar materials, their characteristics, and techniques to improve their joining performance. The joint strength for each joining method is also summarized in this study. The joining methods are primarily divided into mechanical joining, chemical joining using adhesives, and thermal fusion welding. Methods to enhance the joint include combining each joining method and improving surface interactions through surface treatments. The joint exhibiting the highest strength was the laser-welded joint of strength 312 MPa between Ti3Al-Nb alloy and Ni-based superalloy, while the lightest and strong joint was the friction stir-welded joint of strength 63.4 MPa in Polyamide 6 GFRP. Welded joints of polymer materials appear promising for the future mobility industry, particularly in terms of being lightweight. Additionally, there is a need to develop new methods to measure strength as the units used to represent the physical characteristics of the joints are not standardized. Some joints suffer from issues due to unclear joint area, highlighting the necessity to develop new strength measurement methods for future advancements.

Owing to the high strength and plasticity, high-entropy alloys (HEAs) can be used as filler metals to achieve high-quality joints. However, the melting base metal in fusion welding can significantly change the chemical composition of the weld zone (WZ), which may cause the failure of high-entropy effects in the WZ. In the present study, a high-entropy filler metal of CoCrNiMnAl0.6Ti0.3Si0.1 was used to join the dissimilar metals of SMA490BW steel and 304 stainless steel. Two types of joints were obtained by whether the welding plates had a V-groove or not. The effects of workpiece groove on the microstructure, element distribution, phase structure, microhardness, and tensile strength of dissimilar joints, as well as the controllability of the high-entropy effects in WZ were explored. It was found that a 60° V-groove in the workpiece could significantly reduce the amount of Fe element in the WZ. Microstructures in the WZs were changed from columnar/equiaxed grains of the No V-groove sample to lamellar structures of the V-groove sample. The microhardness in the WZ of the latter was 33% higher than that of the former. The reason was mainly related to the phase structures in two WZs. Two types of samples had a similar notched tensile strength, which was higher than SMA490BW steel, and lower than 304 stainless steel.

Exit-holes in friction stir welded dissimilar aluminum-copper (Al–Cu) joints are repaired by using probeless tools, forcing the surrounding material to fill the exit-hole cavity. The repair by refilling the same base materials is performed in two steps using probeless tools of different diameters. In this study, two different conditions are investigated, keeping the processing parameters constant and varying the tool shoulder diameters. Namely, the repair is performed using a two steps sequence of probeless tools with shoulder diameters of: (1) 12 and 19 mm, and (2) 12 and 27 mm. The refill action is achieved using only the base materials. A comprehensive experimental campaign, including tensile tests, microhardness measurements, scanning electron microscopy and energy dispersive x-ray spectroscopy investigations, have been conducted to evaluate the effectiveness of the repairing. The results showed that the usage of probeless tool is an effective strategy to repair the exit-hole of dissimilar Al–Cu friction stir welds, with exclusive contribution from the same Al and Cu base materials in the cavity of the exit-hole. The original FSW joint with exit-hole, with a diameter of about 8 mm, repaired by shoulder diameters of 12 and 19 mm exhibited ultimate tensile strength about 13% higher than the values provided by the samples taken in the steady-state region of the weld bead The maximum and minimum hardness of the repairing zone made with shoulder diameters of 12 and 19 mm are 240 and 80 HV0.1, respectively, which are within the range of the friction stir welded regions indicated in previous studies.

Friction stir welding (FSW) method becomes an effective technique for welding dissimilar alloys such as AA2024 and AA5083 as the conventional fusion welding methods are not very suitable for welding the dissimilar alloysand cause many defects during solidification process. Since the strength of FSWedjoints depends on the process parameters, a new method was used in this study to predict the tensile behavior of friction stir welded AA5083 and AA2024 aluminum alloy joints in terms of tensile elongation (TE) and ultimate tensile strength (UTS). A new metaheuristic algorithm called Marine Predators Algorithm (MPA) has been integrated with Random Vector Functional Link (RVFL) network to improve the prediction accuracy. Rotational speed, welding speed, tool axial force, and pin profile were used as input parameters while UTS and TE works as the corresponding outputs. The MPA-RVFL model was tested and validated,a great agreement was demonstrated between the experimental results and the predicted results indicating that the developed technique is accurate and reliable to predict the tensile behavior of welded aluminum joints.

To combine the advantages of ductile fillers and composite fillers and alleviate residual stress in joints between ZrB2-SiC ceramics (ZS) and TC4-TiBw composites, a novel multi-layered joint architecture composed of a layer of clustering SiC at the center of the joint (L-C-SiC) and two ductile layers without SiC particles bordering both substrates (L-DS) was designed. To achieve this, SiC particle skeletons with continuous micro-channels (SSCC) were integrated with AgCu filler as an interlayer. The effects of SSCC porosity and brazing temperature on joint microstructure and mechanical properties were investigated. In particular, the braze/ZS and braze/SSCC interfaces were analyzed through X-ray diffractometry (XRD), transmission electron microscopy (TEM), and wavelength-dispersive spectroscopy (WDS). The residual stress was also evaluated. The results indicate that increasing the brazing temperate improved the infiltration into the SSCC and promoted the SSCC/braze interface reaction (was detrimental to the SiC particle skeleton). Reducing the SSCC porosity changed the thicknesses of the two L-DSs and enhanced the inhomogeneity of the SSCC/braze interface reaction (induced a shear stress in L-C-SiC). For brazing with an interlayer of 30% porosity at 820 °C, the joint shear strength reached a maximum of ~41.2 MPa, mainly due to the construction of the multi-layered joint architecture.

A study is conducted to investigate the microstructure and mechanical properties of lap joints produced by friction stir welding (FSW) between 3.5 mm thick sheets of automotive aluminum alloys AA6082-T6 with AA6063-T6. The FSW tool used in this study includes a set of WiperTM scrolls on the shoulder face and a probe having right hand threads, a set of tapered flats, and a set left hand CounterFlowⓇ grooves. The FSW process parameters are first optimized through the use of Design of Experiments (DOE) methodology. Static lap-shear tests are performed on the DOE coupons to identify the optimized parameters and once an optimized set of process parameters is identified, lap joint coupons are fabricated from sheets of each alloy for further mechanical and metallurgical investigation. The study implemented post-weld material characterization tests alongside a novel real-time feedback signal monitoring method for assessing the properties of friction stir lap welds. The analysis included microstructural examination, microhardness testing, lap shear testing, and an advanced electronic non-destructive evaluation (e-NDE) technique that uses the process feedback forces to detect weld anomalies primarily in the form of voids in real time. The analysis includes microstructural examination, microhardness testing, lap shear testing, and an advanced electronic (signal/frequency analysis) non-destructive evaluation (e-NDE) technique in order to detect weld anomalies primarily in the form of voids. For comparison purposes, the specimens are tested under two different loading scenarios; loading of the advancing side, and loading of the retreating side. During FSW, the plasticized material is dragged by the tool from the retreating side of the weld to the advancing side around the rear of the tool. Each loading scenario is tested for three conditions; as-welded, naturally-aged, and post-weld heat treated. The weld produced by the optimized parameters was fully consolidated and had no volumetric defects; absence of hooking is clearly identified in the microstructural analysis of the dissimilar lap joint along with good material flow and mixing of the alloys. The ‘advancing-side-loading’ is found to perform with higher strength than the ‘retreating-side-loading,’ which is evidence that ‘retreating-side-loading’ is less favorable in the FSW lap joints produced in this study because of weaker weld strength in the retreating side. A finite element modeling procedure is utilized to examine the distribution of stresses and displacements in a shear test of a lap weld sample. This study identifies improved process parameters for friction stir welding of dissimilar aluminum alloys for enhanced performance.