Microstructure and mechanical properties of AZ91D alloy prepared by a semi-solid diecasting process

Semi-solid processing has been combined with die-casting for the magnesium alloy AZ91D. The microstructure of the semi-solid diecast AZ91D has been examined by optical microscopy and scanning electron microscopy. No pores were visible under optical microscopy, indicating a very low porosity. Mechanical properties of the semi-solid diecast AZ91D alloy have also been tested. High ultimate tensile strength and elongation have been achieved due to the low porosity and the fine microstructure. The fracture surfaces have been investigated by scanning electron microscopy in order to reveal the fracture mechanism. A typical inter-granular fracture surface was observed, indicating that the alloy fails in a brittle manner. The vertical-section microstructure of the fractured sample has indicated that the crack mainly propagates along the grain boundaries through the brittle fracture of the eutectic phase or the interface decohesion of the primary Mg phase and the eutectic phases.