Effects of Magnesium Aluminides on Dissimilar Metal Laser Welds between Magnesium Alloy and Aluminum Alloy

摘要

Dissimilar metal laser welding of magnesium alloy AZ31B and aluminum alloy 6061 was conducted on both lap and butt joints. Magnesium aluminides(MgAls) β-Mg_2Al_3 andγ-Mg_(17)Al_(12) were identified in laser welds which affected weldability and joint properties. The weld microstructure exhibited three distinct regions as a narrow fusion band, an MgAl depleted zone and a dense MgAl dendrite zone. The fusion band is composed of α-Mg and γ-Mg_(17)Al_(12) eutectic and nonepitaxially grown MgAl column dendrites. MgAl depleted and dense dendrite zones of lap welds consist of β-Mg_2Al_3 phase and Al solid solution matrix, while Mg solid solution is an additional matrix constituent in butt welds. Limited tensile strength is achieved of the butt welds. Failure occurred in the interfacial region of MgAl depleted zone and dense dendrite zone. The marginal weld strength is attributed to the relatively tougher MgAl depleted zone characteristic of quasi-cleavage.