Phase selection of ternary intermetallic compounds during solidification of high zinc magnesium alloy

摘要

The phase selection of ternary intermetallic compound τ phase (Mg32 (Al,Zn)49) and φ phase (A12Mg5Zn2) in high zinc magnesium alloys was studied by using scanning electron microscope,X-ray diffractometer and differential scanning calorimeter,etc.The results indicate that,when adding element Si in Mg-8Zn-4Al-0.3Mn (ZA84) alloy,φ phase is promoted,whereas τ phase is inhibited.The Chinese script-type Mg2Si and matrix microstructure are greatly refined,the formation of τ phase is facilitated and φ phase is restrained when modifier Al-AlP master alloy is added in ZA84 alloy containing Si.The kinetics study of phase selection indicates that there is a critical degree of undercooling of the melt.If the undcrcooling exceeds the critical value,τ phase preferentially forms while φ phase is restrained; otherwise,φ phase preferentially forms while τ phase is restrained.