Microstructure control of AZ31 alloy by self-inoculation method for semisolid rheocasting
(1. State Key Laboratory of Gansu Advanced Nonferrous Metal Materials,
Lanzhou University of Technology, Lanzhou 730050, China;
2. Key Laboratory of Nonferrous Metal Alloys and Processing, Ministry of Education,Lanzhou University of Technology, Lanzhou 730050, China)
Lanzhou University of Technology, Lanzhou 730050, China;
2. Key Laboratory of Nonferrous Metal Alloys and Processing, Ministry of Education,Lanzhou University of Technology, Lanzhou 730050, China)
Abstract: A novel rheocasting process, self-inoculation method (SIM), was developed for the microstructure control of semisolid wrought Mg alloy. This process involves mixing between liquid alloy and particles of solid alloy (self-inoculants), subsequently pouring the mixed melt into a special designed multi-stream fluid director. The primary phase with dendritic morphology in the conventionally cast AZ31 alloy has readily transformed into near spherical one in the slurry produced by SIM from melt treatment temperature between 690 °C and 710 °C and self-inoculants addition of 3%-7%. Achievement of the non-dendritic microstructure at the higher melt treatment temperature requires more self-inoculants addition or decreases in the slope angle of fluid director. Primary phase in the slurry thus produced has attained an ideally globular morphology after isothermal holding at 620 °C for 30 s. The increasing holding time leads to decrease of shape factor but the coarsening of particle size. The spheroidization and coarsening evolution process of solid particles during the isothermal holding were analyzed by Lifshitz-Slyozov-Wagner (LSW) theory.
Key words: AZ31 alloy; microstructure; semisolid rheocasting; self-inoculation method