利用高分辨透射电镜和扫描电镜分析了Mg-4Zn-2Al-0.5Ca合金时效沉淀过程中的相演变。结果表明：试验合金的时效硬化曲线呈现典型的时效硬化特征。试验合金在160℃时效达到峰值硬度时其沉淀相有：平行于（0001）Mg的圆盘状沉淀相、（梳齿状）块状沉淀相以及大量的亚稳过渡相。随时效时间的延长,生成长条状相,但基体中依然存在很多后析出的细小的弥散分布的粒状沉淀相。120℃×230 h时效处理后的微观组织中存在着蜂窝状组织,宽度为3～4 nm的长条状沉淀相,直径为5～7 nm的球状沉淀相;这些沉淀相的存在大大提高了合金的硬度。
Evolution of precipitated phases in the process of ageing treatment of Mg-4Zn-2Al-0.5Ca alloy was investigated by transmission electron microscopy（TEM） and scanning electron microscopy（SEM）.The results indicate that precipitation hardening curves of the alloy show a typical characteristic of aging at different temperatures.The alloy reaches peak hardness,containing disc shaped and block shaped precipitates and a large number of metastable transition phase after ageing at 160 ℃ for 108 h.With prolonging of aging time,elongated precipitates are formed,but a lot of fine and dispersively distributed precipitate particles are still observed in the matrix.The microstructure of the alloy is honeycombed with long strip-shaped precipitates about 3-4 nm in width and disc precipitates about 5-7 nm in diameter after ageing at 120 ℃ for 230 h.These precipitates significantly increase the hardness of the alloy.
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