真空离心铸造冷却速率对7055铝合金组织和力学性能的影响

采用真空离心铸造技术制备了7055铝合金铸管，通过添加中间包进行保温来改变合金凝固冷却速率，并对铸管进行组织和性能测试.结果表明，冷却速率较慢的1#铸管组织分布不均，其晶粒沿着外、中、内层由等轴晶逐渐变为粗大树枝晶，且晶粒间分布着更多的第二相；而冷却速率较快的2#铸管组织均为细小的等轴晶，且分布着少量的第二相.经过均匀化后，两种铸管的第二相分布数量由外、中、内层逐渐增多，且1#铸管残余的第二相数量更多;合金硬度值较铸态时有所增大，但2#铸管硬度值增大幅度更大，拉伸性能优于1#铸管.

Effect of the Cooling Rate of Vacuum Centrifugal Casting on Microstructure and Mechanical Properties of 7055 Aluminum Alloy

Casting tubes of 7055 aluminum alloy were prepared by the vacuumed centrifugal casting technology. The cooling rate of the casting was changed by the addition of the tundish and the corresponding microstructure and mechanical properties of the alloys were studied. The results show that the microstructure of the casting tube sample with the slow cooling rate(Casting tube 1#) is unevenly distributed. The grains change from the equiaxed grains to the coarse dendritic ones along the solidification direction of the cross-section plane， and some second phases are distributed at the grain boundaries. However， the microstructure of the casting tube sample with the fast cooling rate(Casting tube 2#)consists of the fine equiaxed grains and a small amount of second phases. After homogenization process， the amount of second phases along the solidification direction in both samples increase gradually， and the second phases of Casting tube 1# is greater， while the hardness increment and the tensile properties of Casting tube 2# is higher.