Modification of primary Mg2Si in Mg-5Si alloys with Y2O3
(Key Laboratory of Automobile Materials of Ministry of Education,
Department of Materials Science and Engineering, Jilin University, Changchun 130025, China)
Department of Materials Science and Engineering, Jilin University, Changchun 130025, China)
Abstract: The Y2O3 addition to Mg-5Si alloys has a good modification effect on the primary Mg2Si. With 0.05% or 0.1% (mass fraction) Y2O3 additions, the primary Mg2Si begins to change from coarse dendritic shape (about 100 mm) into small polyhedral shape and therefore the alloys exhibits sub-modified microstructure. With 0.2% Y2O3 addition, most of the primary Mg2Si becomes polyhedral shape and its average size is only 25 mm or less. The Mg-5Si alloy exhibits modified microstructure. In addition, the experiments show that the reaction between Mg and Y2O3 cannot occur in the sintered Mg-6Y2O3 compact; however, the reaction among Mg, Si and Y2O3 can occur in the sintered Mg-5Si-6Y2O3 compact. Apart from the adsorption and poisoning manners, other mechanisms may exist in the modification of Y2O3 addition on the primary Mg2Si.
Key words: microstructure; solidification; Mg2Si; Y2O3; Mg-5Si alloy