Effect of holding time on microstructure of Mg-9Al-1Si alloy during
semisolid isothermal heat treatment
(Center for Biomedical Materials and Engineering, College of Materials Science and Chemical Engineering,
Harbin Engineering University, Harbin 150001, China)
Harbin Engineering University, Harbin 150001, China)
Abstract: The effects of isothermal holding time on the semisolid microstructure of Mg-9Al-1Si (mass fraction,%) alloy were investigated. The research results indicate that the Mg-9Al-1Si alloy with non-dendritic microstructure can be produced by the semi-solid isothermal heat treatment. With holding time varying from 5 to 30 min, the volume fraction of liquid is gradually enlarged from 29.3% to 38.6%, the morphology of α-Mg grains changes from initial dendritic shape to spherical types and their average sizes increases from 41.1 to 56.1 μm. In addition, during the isothermal heat treatment, the eutectic Mg2Si phase changes from the initial Chinese script shape to granule and/or polygon shape in Mg-9Al-1Si alloy. The modification of Mg2Si phase is possibly attributed to a shift of the eutectic composition of the liquid in semi-solid slurries, towards lower silicon contents with increasing Al content due to a redistribution of Al during isothermal heat treatment.
Key words: Semi-solid; isothermal heat treatment; Mg2Si phase; modification