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In order to improve welding efficiency and joint performance of friction stir welded aluminum alloy plates of different thickness, a new synergistically double-sided friction stir welding (SDS-FSW) technique was developed and investigated. The microstructure and mechanical properties of SDS-FSW, conventional single-sided FSW (SS-FSW) and conventional sequentially double-sided FSW (CDS-FSW) 6 mm thick 6061 aluminum alloy joints were systematically investigated and compared. The temperature field and material flow of these joints during welding were studied with numerical modelling. Results show that the microstructure of SDS-FSW joints is uniform and sound, with grains and second-phase particles in the weld nugget zone refined. When compared with the other two FSW processes, there is higher heat input and improved material flow in the SDS-FSW process at 1400 rpm and 600 mm/min. The microhardness and microstructure of the SDS-FSW joints are uniform along the weld thickness. The tensile strength is comparable to BM, while considerably higher than that of SS-FSW joints. In addition, when the upper and lower tools rotate in opposite directions, joint microstructure improved further.

The growing demand for lightweight materials in the automotive and aerospace industries has driven research on joining dissimilar lightweight alloys, particularly Al and Mg alloys (Al/Mg). Friction stir welding (FSW) is a promising technique for joining Al/Mg alloys, as it works below the base metal's melting temperature, leading to refined microstructures, reduced porosity, and enhanced productivity. The strength of Al/Mg friction stir weldment depends on the evolved interface, which is primarily characterized by micromechanical interlocks, type, and intermetallic compounds (IMCs) distribution. Different interfaces for butt joints have been discussed in the literature. However, the mechanism of interfacial interaction together with the ways to enhance the interface have not been reviewed yet. This review article fills the gap by analyzing the retrospective data for process parameters and mechanical properties. Joining mechanisms and the evolution of different interfaces at the microstructural level have been discussed. Lastly, ways to enhance the interface for improved mechanical properties are explained. By offering essential insights into FSW techniques and Al/Mg weld interfaces, this review article paves the way for developing FSW procedures for Al/Mg butt welds aiming for enhanced strength and performance. This review article is expected to be of interest to researchers and engineers working in the field of FSW, particularly for Al/Mg lightweight applications. It provides an overview of the current state of knowledge and identifies key areas for future research.

In recent years, the cost-effective wire arc additive manufacturing (WAAM) method is increasingly replacing traditional production methods for Ni-based superalloys. However, the effect of high heat input and elemental segregation in the WAAM method on machinability has not yet been adequately investigated. For this purpose, drilling of wrought and WAAM Inconel 625 samples with thermal (i.e., die-sinking micro-EDM and micro-EDM) and mechanical drilling techniques (i.e., orbital and conventional drilling) was investigated in this study. It was observed that thermal drilling methods formed a white layer with a thickness of 20-25 μm and 35-50 μm in the cross-section of wrought and WAAM specimens, respectively, while no white layer was formed in the mechanical methods. The average surface roughness of the inside hole, Ra, obtained in the conventional drilling process has improved by 46.15 %, 94.62 %, and 92.82 %, compared to the orbital, die-sinking, and micro-EDM methods, respectively. Because the drill cutting form and helix angle used in this method facilitated chip evacuation. The best surface roughness was obtained respectively by conventional (0.27–029), orbital (0.51–0.53), die-sinking (4.54–5.88), and micro-EDM drilling (3.54–4.25) methods. In addition, a larger kerf angle is obtained in the WAAM sample compared to the wrought one due to higher residual stress and higher dislocation density in the WAAM alloy. On the other hand, the higher hardness value of WAAM samples provided better surface quality in mechanical drilling methods than wrought material. An increase in surface hardness values up to 25 μm from the surface was detected due to the recast layer formed in thermal drilling methods and the strain hardening occurring on the surface in mechanical drilling methods.

In this study, the weldability of lower strength St 37 grade steel plate with a higher strength steel plate (i. e., St 44) using the friction stir welding technique has been studied. St 37 grade steel sheets are widely used in various industries. However, the joining of St 37 steel plates with higher strength grades such as St 44 grade steel is usually required when the strength of St 37 grade is not sufficient. Therefore, microstructural and mechanical properties of friction stir welded St 37-St 44 butt joints were investigated by conducting optical microscopy, microhardness measurements, and tensile testing. A fine-grained recrystallized microstructure was observed in the weld regions of the joints produced. The highest tensile strength, i. e. 385 MPa, was exhibited by the joint produced at 630 rev × min-1.

The present study deals with laser beam welding (LBW) and friction stir welding (FSW) applied to high-strength aluminum alloys used in aircraft industry and displays their advantages compared with the riveting technique regarding structural integrity, weight and material savings. First of all, it is shown with respect to different applications and strength levels which high-strength aluminum alloys represent the state-of-the-art and which aluminum alloys are proposed as substitutes in the future. Furthermore, the respective joining process principles are described and demonstrated on different joint configurations, whereby mechanical and microstructural properties of laser beam- and friction-stir-welded joints are discussed and compared. The current study clearly demonstrates that these two joining techniques are not competing but complementary joining techniques in the aircraft industry.

The present study investigates the microstructure and mechanical properties of the Co-free FeNiMnCrAlTi high-entropy alloy (HEA) after casting, homogenizing heat treatment, and hot rolling. The results show that the dendrite regions in the as-cast state were enriched in Cr and Fe and inter-dendritic regions were saturated with Ti and Al. By homogenizing heat treatment, the dendritic solidification structure is eliminated. Furthermore, the microstructure was refined after hot rolling. The EDS and XRD analyses show that despite the matrix and secondary phases' different chemical compositions, their crystal structures are the same. The as-rolled HEA revealed an excellent compromise in mechanical properties: 720 MPa yield strength, 922 MPa ultimate tensile strength, and 30% elongation. A typical ductile failure was observed on the fracture surface of the as-rolled HEA.

Controlling the amount of distortion and tensile residual stresses plays an important role during welding of high strength steels. The amount of distortion and residual stresses in high strength steel welds may be reduced and compressive residual stresses can be induced by lowering the transformation temperature with the use of low-transformation-temperature (LTT) welding electrodes. In this study, high strength Domex 500 plates (500 mm ´ 300 mm ´ 7 mm) were welded with conventional high strength electrodes and LTT filler electrodes with a diameter of 2.5 mm. The objective of the study is to compare the mechanical and microstructural properties of high strength steel joints (i.e., Domex 500) produced using both conventional electrodes and newly-developed prototype LTT electrodes.