Effects of reheating temperature and time on microstructure and tensile properties of thixoforged AZ63 magnesium alloy

Abstract

The effects of two main processing parameters such as reheating temperature and reheating time on microstructure and tensile properties of thixoforged AZ63 magnesium alloy have been investigated. The results indicate that these two parameters all have large effects on the microstructure and tensile properties. However, in contrast, the effects of the reheating temperature on liquid fraction and liquid composition of semisolid ingot, and thus the subsequent solidification behaviour and plastic deformation during thixoforging, are larger than those of the reheating time. Therefore, the effects of the former parameter on the microstructure and tensile properties are relatively larger than those of the latter parameter. It is also just this reason that the fracture regime during tensile testing varies as the reheating temperature rises, while the regime always maintains transgranular mode with the variation of the reheating time. Stress concentration that results from the plastic deformation obviously affects the tensile properties, while the primary particle size or grain size only has small effect. The appropriate reheating technique is the heating for 60 min at 595°C when mould temperature is maintained at 350°C. The ultimate tensile strength and elongation of the resulting alloy are up to 310 MPa and 10·7% respectively.

Keywords:

• Magnesium alloy
• Thixoforming
• Microstructure
• Tensile properties
• Fracture

The authors wish to express thanks to financial support from the National Basic Research Program of China (grant no. G2010CB635106), the Program for New Century Excellent Talents in University of China (grant no. NCET-10-0023) and the Program for Hongliu Outstanding Talents of Lanzhou University of Technology.