大尺寸Al-6Mg-0.3(Sc,Zr)合金铸锭铸态和均匀化态微观组织对比

Research on microstructures of as-cast and homogenized large-sized Al-6Mg-0. 3Sc,Zr alloy ingot

采用高分辨电镜、透射电镜、扫描电镜、光学显微镜和显微硬度测试等方法,研究大尺寸Al-Mg-Sc-Zr铸锭均匀性及不同温度均匀化后组织性能的变化。结果表明,大尺寸铸锭铸态组织存在组织和性能不均匀,边部冷却速率高,晶粒小、析出相多、硬度高;中心存在镁偏析。均匀化热处理后,中心镁偏析部分消除,发生固溶强化;铸锭析出Al3(Sc,Zr)粒子起到析出强化作用。高于350℃析出粒子的直径大于临界直径,强化机制为Orowan绕过机制。析出粒子直径越大,强度增量△σOr值减小,温度升高而硬度下降。

The homogeneity of large-sized as-cast Al-Mg-Sc-Zr ingot and its microstructures after homogenization treatment at different temperatures were investigated by HRTEM,TEM,SEM,OM and micro-hardness measurements. The results show that microstructures and properties are inhomogeneous for the large-sized as-cast ingot,with smaller grain sizes,more precipitated phases,higher micro-hardness due to its higher cooling rate on the edge,and with Mg segregation in the center. After homogenization treatment,solid solution strengthens the alloy with Mg segregation partially disappearing,and Al3（ Sc,Zr） particles precipitate from the ingot cast and strengthen the alloy by precipitation strengthening. When the temperature increases higher than 350℃,the particles＇ average diameter exceeds the threshold. As a result,the strengthening mechanism is Orowan bypass mechanism. As the particle diameter increases,the strength increment △σOrdecreases. While the micro-hardness decreases with the heating temperature increasing.