Microstructural characterisation and liquation behaviour of laser welded joint of fine grained AZ91 magnesium alloy thin sheets

Abstract

Fine grained AZ91 sheets of 1 mm in thickness were successfully welded by autogenous laser beam welding and laser beam welding with filler strip. Both welded joints are characterised by fine equiaxed dendrites in the fusion zones and free from significant grain coarsening in the heat affected zones. There are two kinds of liquation reactions in the partially melted zone of the autogenous laser beam welding joint, which are associated with the melting of residual bulky β-Mg 17 Al 12 phase and the constitutional liquation of submicrometre β-Mg 17 Al 12 precipitates. No liquation reaction is detected in the welded joint obtained by laser beam welding with filler strip. The laser beam welding joint with filler strip for AZ91 thin sheets is free from evident collapse.