Unravelling the influence of CMT characteristic parameters on process stability and joint properties in dissimilar aluminium-steel weld-brazing

Abstract

This study evaluates the stability and performance of Cold Metal Transfer (CMT) weld-brazed joints by examining the effects of boost current, boost duration, wait current, and wire feed rate (WFR) during the wait phase. Process stability improves on increasing boost current, while longer boost durations (>4 ms) or higher wait currents (>80 A) can cause instability due to arc disturbances and premature filler deposition. The WFR influences the deposition frequency but does not significantly impact stability. Wettability improves with increased boost current, boost duration, and wait current. However, excessive wettability can cause processing-induced defects such as solidification cracking due to both reduced cross-sectional area and presence of highly brittle intermetallic layer. The thickness of the intermetallic layer grows with increasing heat input. Shear-tensile tests revealed that the failure load rises with boost current, duration, and wait current up to an optimal level, then declines primarily due to excessive intermetallic layer thickness (>5 μm). The failure modes varied with layer thickness and wettability, with the highest load observed at a WFR of 10 m/min.