The friction stir welding (FSW) process was recently developed to overcome the difficulty of welding non-ferrous alloys and steels. In this study, dissimilar butt joints between 6061-T6 aluminum alloy and AISI 316 stainless steel were welded by FSW using different processing parameters. The grain structure and precipitates at the different welded zones of the various joints were intensively characterized by the electron backscattering diffraction technique (EBSD). Subsequently, the FSWed joints were tensile tested to examine the mechanical strength compared with that of the base metals. The micro-indentation hardness measurements were conducted to reveal the mechanical responses of the different zones in the joint. The EBSD results of the microstructural evolution showed that a significant continuous dynamic recrystallization (CDRX) occurred in the stir zone (SZ) of the Al side, which was mainly composed of the weak metal, Al, and fragmentations of the steel. However, the steel underwent severe deformation and discontinuous dynamic recrystallization (DDRX). The FSW rotation speed increased the ultimate tensile strength (UTS) from 126 MPa at a rotation speed of 300 RPM to 162 MPa at a rotation speed of 500 RPM. The tensile failure occurred at the SZ on the Al side for all specimens. The impact of the microstructure change in the FSW zones was significantly pronounced in the micro-indentation hardness measurements. This was presumably attributed to the promotion of various strengthening mechanisms, such as grain refinement due to DRX (CDRX or DDRX), the appearance of intermetallic compounds, and strain hardening. The aluminum side underwent recrystallization as a result of the heat input in the SZ, but the stainless steel side did not experience recrystallization due to inadequate heat input, resulting in grain deformation instead.

Attempt was made to improve the surface hardness and wear properties of AISI M2 high speed tool steel. Laser surface melting (LSM) of tool steel was conducted with 2.2 KW Nd:YAG laser as heating source. Conventional hardening of the tool steel was applied. Characterizing the LSM, with optical and field emission scanning electron microscopy and surface hardness technique was used to evaluate the micro-hardness and mechanical behaviour of different regions of melting pool. AISI M2 tool steel is approximately HV 260, hardness after conventional treatment was 850 HV and the hardness after laser surface heat treatment is around 900 HV. It was found that there is a considerable influence of the laser power density and scanning velocity on the melted zone dimensions and the re-solidified structure. Increasing laser energy and reducing the laser scanning rate results in deeper and wider melt pool formation.

Plasma arc machining (PAM) has emerged as a cost-effective alternative to laser cutting forsheet-metal fabrication. However, thermo-fluid interactions during plasma cutting of ultra-thinbrass sheets remain insufficiently understood because of the material’s high thermal sensitivityand susceptibility to heat-induced damage. In particular, the combined effects of arc current andtraverse speed on kerf formation and surface integrity have not been systematically clarified forthin brass sections. Therefore, this study investigates the thermo-metallurgical behavior of 0.8mm brass sheets during plasma arc cutting using a Taguchi L16(4²) experimental design. Theinteraction between arc current and traverse speed was evaluated through kerf geometry, surfaceroughness, heat-affected zone (HAZ) evolution, microstructural changes, and hardnessdistribution to determine stable low-damage cutting conditions.The results showed that cutting performance is governed by the interaction between heat inputand melt-ejection stability. Higher arc current increased localized melting, resulting in greaterdross adhesion, kerf widening, and grain coarsening within the HAZ. Increasing traverse speedreduced thermal exposure and improved kerf quality; however, excessively high speeds slightlydegraded surface finish because of unstable molten-material evacuation. Microstructural analysisindicated that thermal accumulation controlled grain growth behavior, whereas hardnessremained nearly unchanged due to shallow thermal penetration in thin-sheet machining. Optimalcutting conditions were achieved at 30 A and 1500 cm/min, producing minimal kerf deteriorationand limited microstructural damage. These findings provide insight into heat-input control andmelt-flow stability during plasma cutting of thermally sensitive copper-based alloys.