研究了添加Si对Zn?38Al?2.5Cu合金显微组织、力学性能及热疲劳性能的影响。结果表明：Si的添加使锌铝合金产生成分过冷。当Si添加量为0.55%时，合金组织细化显著，力学性能最优。继续添加Si，Si相聚集长大，晶粒粗化，合金力学性能下降。由于塑性变形形成的凹坑及氧化是热疲劳裂纹萌生的主要原因。在裂纹扩展前期，裂纹附近形成的疏松多孔的氧化区加快裂纹生长，符合 Paris 公式，裂纹主要沿晶界扩展。裂纹扩展后期，二次裂纹的快速生长吸收了主裂纹生长所需的部分能量，裂纹进入缓慢增长阶段，裂纹变为沿晶和穿晶混合的扩展特征。
The influence of Si addition on microstructure, mechanical properties and thermal fatigue behavior of Zn?38Al?2.5Cu alloys was investigated. The results show that constitutional supercooling of ZA38 alloys is formed because of the Si addition. Zn?38Al?2.5Cu?0.55Si alloy shows the dramatically refined microstructure and the best mechanical properties. When the Si addition exceeds 0.55%,αdendrites develop and Si phases become larger and aggregate along the dendrites boundaries, decreasing the mechanical properties. Oxides and pits formed by the plastic deformation are the main factors of cracks initiation. During the early stage of crack propagation, the cracks grow at a high speed well described by Paris law because of the porous and loose oxide, and mainly propagate along the dendrites boundaries. During the slow-growth stage, secondary cracks share the energy of crack growth, delaying the propagation of cracks, and the cracks propagate and fracture by the mixture of intergranular and transgranular modes.
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