Neutron diffraction study on TIG dissimilar welding of AZ31 Mg alloy and 6061 Al alloy using ER5356 filler metal

Abstract

Mg alloy and Al alloy have many applications in many industries, and dissimilar joint between each alloy is necessary. Tungsten inert gas (TIG) is a welding technique which has been considered promising to weld between Mg alloy and Al alloy. However, the quality of the joint still remains as attractive issues. The main problem is the formation of brittle intermetallic compounds (IMC) in the fusion zone. Choosing proper filler metal is an alternative way to minimize the IMC formation. The purpose of this research is to study the phase composition and crystal structure of TIG-welded AZ31 Mg alloy and 6061 Al alloy by means of neutron diffraction. ER 5356 filler metal was used due to its excellent weldability and it was particularly fabricated for welding Al/Mg alloys. The welded sample was mounted on the sample table with the welding direction being perpendicular to the neutron beam. After careful beam alignment, neutron diffraction experiment was conducted on several zones including the fusion zone (weld area), heat affected zone (HAZ) of both Mg and Al side, as well as the base metal zone. The results showed the domination of Al phase in the weld area. Unusual peaks correspond to small amount of IMC phases were still found in the weld area. Al phase experienced lattice swelling and suppressed the Mg phase on its c axis.