Cold Metal Transfer joining of magnesium AZ31B-to-aluminum A6061-T6

In this study, welding of 1 mm thick magnesium AZ31B-to-1 mm thick aluminum A6061-T6 using a 1.6 mm diameter aluminum filler wire 4047 was investigated. Cold Metal Transfer (CMT) arc welding technique was adopted. The key feature of this process is that the motion of the wire has been integrated into the overall control of the process. The wire retraction motion assists droplet detachment during the short circuit, thus the metal can transfer into the welding pool without the aid of the electromagnetic force. In this way the heat input and spatter can be controlled and the IMP formation minimized thereby improving the joint strength. Extensive experiments were performed and analyzed. It was found that although extensive efforts have been exercised to control the heat input, Mg-rich intermetallic γ-Al12Mg17 and Al-rich intermetallic β-Al3Mg2 were still produced in the weld. Fracture surfaces of CMT welded AZ31B-Al6061-T6 joints exhibited the Mg-rich intermetallic (γ-Al12Mg17) which contributes to the weld strength degradation. To improve the joint, minimizing the content of the intermetallics especially Mg-rich intermetallics (γ-Al12Mg17) is essential.