Effects of liquid cooling rate (VLC) and Zn content on microstructures and mechanical properties of unidirectionally solidified and T5-treated Mg-4.0%RE-0.7%Zr-x%Zn alloys (x=0, 2.2, 3.1, 3.9 and 5.7) were investigated. Equiaxed grain size reduces with acceleration of VLC. The amount of Mg-RE-Zn eutectic compounds increases as VLC and Zn content in the alloys increase. Zn in the matrix of as-cast alloys is condensed with decreasing VLC and with increasing Zn in the alloys. Tensile strength,

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... gation, and impact properties decrease, but 0.2% proof stress and Brinell hardness increase with increasing Zn content in the alloys. The T5-treated alloys strengthen proportionally with Zn content in the matrix of solidified structures. Tensile properties, Brinell hardness, maximum load and crack initiation energy are improved as VLC increases.