Effects of mould temperature and grain refiner amount on microstructure and tensile properties of thixoforged AZ63 magnesium alloy

The effects of mould temperature and addition amount of MgCO3 refiner on the microstructure and tensile properties of thixoforged AZ63 alloy have been investigated. The results indicated that both the mould temperature and addition amount of MgCO3 refiner have large effects on the microstructure and tensile properties of the thixoforged AZ63 alloy. The mould temperature affects the solidification behavior, plastic deformation and recrystallization during thixoforging through changing solidification rate. But the effects of the refiner are realized through altering the morphology and size of primary alpha-Mg particles and the Al content of liquid phase. Generally, high mould temperature or high refiner addition amount are beneficial for obtaining a compact microstructure with uniform deformation, and thus for improving tensile properties. The properties with ultimate tensile strength of 310 MPa and elongation of 10.7% can be obtained using the thixoforging. Crack propagation path during tensile testing changes from completely or partially along the secondarily solidified structures between the primary particles to completely across the alpha-Mg particles as the temperature or the refiner addition amount increases. Work hardening from the plastic deformation plays an important role for the tensile properties and this effect also varies with the temperature or the refiner amount. A new technology has been developed for producing AZ63 alloy components with uniform and small grains. (C) 2012 Elsevier B.V. All rights reserved.