均匀化处理对Mg-9.8Gd-3.5Y-2Zn-0.5Zr合金微观组织的影响

Effect of homogenization treatment on microstructure of Mg-9.8Gd-3.5Y-2Zn-0.5Zr alloy

采用DSC、SEM、EDS、OM等检测方法研究了Mg-9.8Gd-3.5Y-2Zn-0.5Zr合金铸锭在505~535℃均匀化处理0~84 h后的组织演变规律。结果表明,铸态组织呈枝晶状,第二相含量为19.86%,晶间第二相主要由白色点状共晶相和块状LPSO相组成,晶内第二相为少量针状LPSO相、花瓣状Zr团簇相和方形富稀土相。均匀化处理后的LPSO相形貌为晶间块状和晶内片层状两种。晶内片层状LPSO相的含量受均匀化温度和均匀化时间的影响。在505~525℃下,晶内片层状LPSO相随均匀化温度的升高,生长速度加快,数量增多。在相同均匀化温度下延长保温时间,晶内片层状LPSO相沿晶界向基体内部析出,贯穿晶粒后开始粗化。535℃下晶间块状LPSO相转变为W相,晶内片层状LPSO相溶解进入基体。晶间LPSO相对晶界迁移起钉扎作用,在505~525℃均匀化,随着保温时间的延长,晶粒长大幅度并不明显。在535℃均匀化,晶间LPSO相大量溶解,晶粒开始急剧长大。

Microstructure evolution of Mg-9.8 Gd-3.5 Y-2 Zn-0.5 Zr alloy ingot after homogenization treatment at 505-535 ℃ for 0-84 h was studied by means of DSC, SEM, EDS and OM. The results show that the as-cast microstructure is dendrite, and the content of the second phase is 19.86%. The intergranular second phase mainly consists of white spot-like eutectic phase and massive LPSO phase, and the intragranular second phase consists of a small amount of needle-like LPSO phase, petal-like Zr cluster phase and square rare-earth rich phase. The morphology of LPSO phase after homogenization treatment is intergranular block and intragranular lamellar. The content of intragranular lamellar LPSO phase is affected by homogenization temperature and time. At 505-525 ℃, the growth rate of intragranular lamellar LPSO phase increases with the increase of homogenization temperature. The intragranular lamellar LPSO phase precipitates along the grain boundary into the matrix with the extension of holding time at the same temperature and begins to coarse after penetrating the grain. At 535 ℃, the intergranular massive LPSO phase transforms into W phase, and the intragranular lamellar LPSO phase dissolves into matrix. The intergranular LPSO phase plays a role of pinning relative to grain boundary migration. Homogenized at 505-525 ℃, with the extension of holding time, grain growth is not obvious. Homogenized at 535 ℃, the intergranular LPSO phase dissolved in large quantities and the grains begin to grow rapidly.