Metallurgical analysis of magnetic pulse welds of AZ31 magnesium alloy

Magnesium AZ31 sheets have been lap welded with magnetic pulse welding using H shaped symmetric coils connected to a Pulsar MPW-25 capacitor bank. The joints displayed an increasing trend in strength with discharge energy. The weld morphology consisted of twin bond zones separated by an unbonded centre zone. Metallographic examination of the unbonded centre zone revealed anisotropic deformation and a lack cleaning from the interface. This zone forms as a result of normal impact in the initial stage of collision. Transmission electron microscopy of the bond zone revealed a continuous interface having an 8–25 μm thick interlayer with dislocation cell structure and distinct boundaries with adjacent material. The interlayer may have formed in a semisolid state at elevated temperature. The interlayer corresponds to a ductile fracture surface and is responsible for the joint's high strength. Nanoscale grains were found beside the interlayer as well as larger, highly elongated grains.