Spheroidal microstructure formation and thixoforming of AM60B magnesium alloy prepared by SIMA process
(College of Materials Science and Engineering, Harbin University of Science and Technology, Harbin 150040, China)
Abstract: The microstructure development in the semi-solid state of AM60B magnesium alloy prepared by strain induced melt activation (SIMA) was described. In the SIMA route, cyclic extrusion compression (CEC) and conventional compression were used to predeform as-cast AM60B, respectively. Partial remelting and thixoforming were also carried out within the semi-solid zone. The results showed that coarse-grained structure disappeared and a fine-grained structure resulted in the CEC formed alloy. However, coarse grains and recrystallized grains co-existed in the compression formed alloy. During partial remelting, the alloy treated by CEC exhibited ideal, fine microstructure, in which completely spheroidized grains contain little entrapped liquid. Polygonal grains were spheroidized to some extent but the previous irregular shape was still obvious in the compression formed alloy. The mechanical properties of the thixoformed AM60B produced by CEC plus partial remelting were better than those of the thixoformed alloy produced by compression plus partial remelting.
Key words: magnesium alloy; microstructure; mechanical properties; thixoforming; partial remelting; cyclic extrusion compression; semi-solid state