中文摘要：

采用MTS809型电液伺服疲劳试验机、扫描电镜研究了不同冷却速度对A319铝合金圆形加载路径下的疲劳特性.结果表明：当冷速为10℃·s~（-1）时,材料中二次枝晶臂间距、硅颗粒及孔洞尺寸较冷速为0.1℃·s~（-1）时要小.二次枝晶臂间距较小时,滞后回线面积小,材料应力应变近乎同相,且附加强化效果明显.不同冷速条件下裂纹萌生位置不同,在冷速为10℃·s~（-1）的材料中,裂纹在大硅颗粒处萌生,随着冷速降低至0.1℃·s~（-1）时,裂纹位于孔洞处萌生.对于A319铸造铝合金来说,冷速的变化对其轴向与切向循环特性并无直接影响,轴向表现为先硬化再软化,切向表现为先硬化后稳定的趋势.

英文摘要：

The effects of cooling velocity on the multiaxial fatigue properties of A319 alloy under circular loading conditions was studied by using the MTS809 servo-hydraulic testing system and scanning electron microscopy.The results indicate that the solidification cooling velocity of 10 ℃·s~（-1）leads to decrease in the size of microstructures,such as second dendrite arming space,Si particle,and void compared.Hysteresis loops with smaller second dendrite arming space show that there is almost no phase angle between strain and stress along the axial direction.Furthermore,the decrease in second dendrite arming space size manifests as a more remarkable additional hardening effect compared to that of the sample with a cooling velocity of 0.1 ℃·s~（-1）.The local regions of crack initiation are completely different.The cracks in samples solidified at a cooling velocity of 10 ℃·s~（-1）initiate and propagate from large Si particulars,in contrast to the cracks in samples solidified at a cooling velocity of 0.1 ℃·s~（-1）,which initiate from pores.It is also found the A319 samples under the two different cooling velocities show initial cyclic hardening followed by cyclic softening in the axial direction and initial cyclic hardening followed by stable tendency in the shear direction.