WELDING OF DISSIMILAR METALS (ALUMINIUM 8000 SERIES WITH ALUMINIUM 6000 SERIES) USING COLD METAL TRANSFER (CMT) WELDING TECHNIQUE

Abstract

The present study investigates the successful fabrication of dissimilar aluminum alloys AA6061 and AA8011 using the Cold Metal Transfer (CMT) welding technique. CMT welding, characterized by its low heat input and stable arc behavior, has emerged as an effective process for joining aluminum alloys with distinct thermal and mechanical properties. This research aims to optimize the key input parameters—welding current, welding speed (WS), and gas flow rate (GFR)—and to evaluate their influence on critical output responses such as ultimate tensile strength (UTS), percentage strain, hardness in the weld fusion zone (WFZ), and residual stress. A comprehensive statistical analysis was performed using Analysis of Variance (ANOVA) to quantify the significance of each input parameter. The results confirmed that all three input variables significantly affected the output responses, as indicated by P-values below the 0.05 threshold. The F-values for UTS (21.96), percentage strain (15.32), hardness (18.13), and residual stress (16.81) further validated the statistical significance of the developed models and the strong influence of input parameters on weld performance. Microstructural characterization revealed that the weld fusion zone predominantly consisted of Mg₂Si precipitates and globular primary α-Al phases, with α-particles aligning along the grain boundaries. The heat-affected zone (HAZ), subjected to a more intense thermal cycle, exhibited a decreased population of α-Al particles and a lower level of precipitate formation, distinguishing its structure from that of the base metal. These microstructural transformations played a critical role in determining the mechanical behavior of the joint. The mechanical testing results highlighted a maximum UTS of 108.74 MPa for sample 11 and a minimum of 72.69 MPa for sample 5. The enhanced mechanical properties, particularly in the WFZ, were attributed to the refined grain structure and the formation of fine secondary phases. The hardness in the weld zone corresponded well with these microstructural features. Residual stress analysis indicated that the maximum compressive stress of -65 MPa occurred at a welding current of 80 A, WS of 10 mm/s, and GFR of 14 l/min. Conversely, the lowest compressive stress of -9 MPa was observed at a current of 60 A, WS of 10 mm/s, and GFR of 18 l/min. These findings underline the crucial role of process parameters in controlling residual stress levels, which in turn affect joint integrity. Through numerical optimization, the ideal set of process parameters was determined to be a welding current of 77.86 A, a welding speed of 9.26 mm/s, and a gas flow rate of 15.26 l/min. At these conditions, the predicted optimized output responses were an ultimate tensile strength of 89.19 MPa, percentage strain of 11.36%, hardness of 78.88 HV, and residual stress of -36.47 MPa.