铸态Mg-3Zn-1Y合金高温热处理显微结构的电子显微研究

SEM-BSE, TEM and HREM observations have been carried out to characterize the microstructural variations for the as-cast Mg-3Zn-1Y (at%) alloys subjected to high-temperature heat treatment at 500℃. The results show that the characteristic network structure formed in the as-cast Mg-3Zn-1Y (at%) alloy is constructed with most primary W-phase (fcc, Mg3Y2Zn3 type) and a small amount of coexisting icosahedral quasicrystal phase (I-phase). After heat treated at 500℃ for 4 hrs, the network structure retained without apparent morphological variation even through the I-phase melted down and disappeared. In addition, a large number of platelet-shaped fcc W'-phases were observed to precipitate in the matrix due to the heat treatment, and relative increase of Zn-concentration in the Mg matrix was also detected. These variations are responsible for the significant hardness enhancement of the heat-treated alloy. HREM observations indicate a ledge growth mechanism for the platelet-shaped W'-phase whose interface exhibits a semi-coherent relationship with the Mg-matrix. The orientational relationships between the W' precipitate phase and the Mg-matrix have been determined to be as follows: [-233]W'∥[110]Mg，(311)W'∥(-110)Mg，(02-2)W'∥(001)Mg.