Preparation of non-dendritic microstructure of AM60 alloy for rheoforming using self-inoculation method

Abstract

A rheocasting process, i.e. self-inoculation method (SIM), has been developed for preparing sound semisolid slurry of AM60 alloy. This process involves mixing between alloy melt and particles of solid alloy (self-inoculants in SIM) and subsequent pouring of the mixed melt with a multistream fluid director. Results show that the combined action of self-inoculants and fluid director can create high nucleation and survive rate of the primary α-Mg phase even with high superheat (85°C) in the AM60 alloy. The melt treatment temperature and addition amounts of self-inoculants are the main factors influencing the slurry microstructure. In order to prepare high quality semisolid slurries, proper melt treatment temperature range of 680–700°C and self-inoculants addition range of 5–7% are suggested. The grain multiplication derives from the heterogeneous nucleation induced by self-inoculants and free crystals and dendrite fragments enhanced by the fluid director; globular grain growth and coarsening of particles should be contributed to the microstructure formation.

Keywords:

• Non-dendritic microstructure
• AM60 alloy
• Semisolid
• Nucleation and survive

This work is sponsored by the Major State Basic Research Development Program of China (973 Program, grant no. 2007CB613700) and the National Natural Science Foundation of China (grant no. 50964010).