Microstructure and mechanical behaviour of semi-solid die-casting AZ91D magnesium alloy

Microstructures and mechanical properties of an AZ91D magnesium alloy prepared with semi-solid die-casting (SSDC) were characterized in as-cast conditions. The SSDC alloy exhibits a unique microstructure featuring primary alpha-Mg globules uniformly distributed in the matrix of fine secondary alpha-Mg grains and beta-Mg17Al12 intermetallic. High ultimate tensile strength and elongation have been achieved before fracture. Observations on the vertical-section microstructure of the fractured sample by scanning electron microscopy (SEM) show that the crack mainly originated from the brittle fracture of the eutectic phase causes the interface decohesion of the ductile Mg phase, making fracture a rather critical event. Before that, the deformation of ductile alpha-Mg phase in the matrix as well as the "pulling out" of primary alpha-Mg phase combines to provide the SSDC alloy a certain strain. (c) 2006 Elsevier B.V. All rights reserved.