In this work, multi-pass friction stir processing (FSP) was successfully applied to AA6061 to reinforce SiC nanoparticles producing defect-free processes. It can be inferred that Nano SiC particles were fragmented totally and uniformly distributed in sixth pass FSP. Agglomeration of SiC particles decreases with increases in the number of FSP pass. In the first pass, the SiC powder with lower formability than the base metal was concentrated inside the groove, so their flow was difficult, and most of them remained at the center of the SZ. The amount of SiC in the surface composite was further decimated after the second pass FSP cycle. At the same time, a progressive and substantial fragmentation of SiC particles ensues after the fourth and sixth passes, respectively, due to improving material mixing and dispersion. The tensile strength of AA6061 exhibited 275.7 MPa, and a percentage strain of 10.9. After implementing multi-pass FSP with nanoparticles of SiC on the AA6061, the tensile properties were enhanced simultaneously as the FSP pass increases. The tensile strength of one pass, two passes, four passes, and six passes was observed as 291.8, 307.5, 330.5, and 348 MPa, respectively, caused by strain-free fine grains during dynamic recrystallization mechanism. In contrast, Vickers’s hardness value along the centerline (stir zone) was observed as 101, 119, 125, and 134 HV with 1, 2, 4, and 6 FSP pass, respectively.

Standard and pulsed gas metal arc welding (GMAW) were performed at a constant welding speed of 300, 600, and 1000 mm/min with eight different wire feed rates (WFR). The effect of input parameters on arc stability, metal transfer mode, penetration depth, hardness, and microstructure was discussed. Voltage and current transients recorded by oscilloscope were used to analyse the arc stability and metal transfer mode by plotting probability density distribution (PDD) graphs of arc voltage and welding current. With an increase in WFR, standard GMAW transformed from bimodal to unimodal (due to the absence of short-circuiting mode and activation of pulsed mode) and the pulsed GMAW graph transformed from multimodal to bimodal (due to faster droplet detachment and lowered background current duration). In addition, a nonlinear mathematical model was generated to adequately predict bead profile parameters. For both standard and pulsed GMAW, maximum penetration depth was achieved at the lowest welding speed and highest WFR. But deeper penetration was achieved in pulsed G compared to the standard for the same input parameters. Hardness and the number of non-diffusional phases in the weld and heat-affected zone (HAZ) increased with welding speed.