Study On The Laser-TIG Hybrid Butt Welding Of Dissimilar Magnesium Alloy And Steel With Cu-Zn Alloy As Interlayer

Magnesium alloys, due to the unique properties, have been considered as promising structure materials to lower weight and energy consumption in automobile industry. However, steels are the most common materials for structural components in the current auto body. The reliable dissimilar combination of magnesium alloys and steel will expand utilization of magnesium alloys in vehicle fabrication. Therefore, it’s drawing increasing attention to join together magnesium alloys and steel to achieve acceptable properties.Preliminary studies have shown that the dissimilar magnesium alloy and steel were lap welded by Laser-TIG hybrid welding with interlayer set in between. The maximum shear strength of direct joint could reach170MPa. However, butt joining of dissimilar magnesium alloy and steel has not been the case of study in hybrid laser-TIG welding process.To further expand utilization of magnesium alloy, the paper focuses on the butt welding of Mg/steel dissimilar joints. In the current experiment, AZ31B magnesium alloy and Q235steel are welded by hybrid laser-TIG welding process with Cu-Zn alloy interlayer. Angle butt welding was investigated, to provide service basis for Mg/steel butt welding.To taking advantage of gradient thermal distribution of hybrid welding, the laser beam shifted to the steel side and the hybrid laser-TIG welding setup was fixed with laser beam ahead of TIG along the welding direction. The sound Mg/steel butt joints with tensile strength of203MPa were achieved with the above method. The effect of Al content in Mg alloys on the interface bonding of Mg/steel dissimilar joints with Cu-Zn alloy interlayer was investigated. The presence of Al could form the reaction-layer along the Mg/steel interface.The joining mechanism of AZ31B/Q235dissimilar joints was studied. the addition of Cu-Zn alloy interlayer, expecially Zn, could significantly lower the reaction temperature of Fe-Al IMCs at the Mg/steel interface and promote the formation of the reaction-layer along the interface. The intimate interface bonding of AZ31/Q235joints could be attributed to the synergistic effect of element Cu and Al. Element Cu sets a bridge between the steel and Mg weld seam due to the dissolving of Cu into the steel and the interaction of Cu/Mg by the formation of MgCuZn. Al content in Mg alloy, forming the reaction-layer of Fe/Al/Mg/Cu/Zn IMCs (about3.66%Fe,11.09%Al,28.38%Mg,37.10%Cu,19.77%Zn (wt.))along the interface, further promotes and strengthens the interface bonding of Mg/steel dissimilar joints.