Investigation of process parameters of cold metal transfer welding-based wire arc additive manufacturing of AA7075 with TiC nanoparticles reinforced filler wire using response surface methodology

Abstract

Al-Zn alloys face difficulties during welding due to the development of secondary phases and solidification cracking. In molten pool solidification, the liquid films present at the boundaries of grains break apart within the mushy region, giving rise to a transitional semi-solid region. The TiC nanoparticles added to filler wire modify the welded material's microstructure, which acts as nucleate during welding. This paper uses TiC nano-treated filler to produce the weld-on-bead of AA7075 alloy through the cold metal transfer (CMT) welding process. To study the effect of input process parameters [i.e., wire feed rate (WFR), welding speed (WS), and gas flow rate (GFR)] on their responses (weld width, weld height, dilution %, and microhardness) were analyzed through response surface methodology (RSM). The central composite face-cantered design matrix was incorporated to assess the model's adequacy through variance analysis (ANOVA). The WFR is the most dominant parameter, followed by the WS and GFR for weld width, height, and microhardness responses. The heat input affects the microstructure of weld beads, and TiC nanoparticles prevent the dislocation and refine the grain size in the fusion zone. The microstructural and microhardness studies were conducted on the WAAM sample fabricated using the optimal input process parameters. The predicted optimal values of WFR, WS., and GFR are 8.5 m/min, 7 mm/s, and 19 L/min, respectively, which provide the maximum weld width of 8.21 mm, weld height of 3.59 mm, microhardness of 158.31 HV and minimum dilution of 33.90% of the weld bead. The microhardness of the bottom, middle, and top regions of WAAM using CMT have obtained 158 ± 2.43 HV, 152 ± 2.34 HV, and 147 ± 2.21 HV, respectively, which depend on the transfer of heat and heat accumulation in the material.