二次时效7055-T7951铝合金微观组织及力学性能

Microstructures and Mechanical Properties of Secondary Aged 7055-T7951 Aluminum Alloy

通过对峰时效与T7951二次时效7055铝合金力学性能测试、微观组织与断口分析,研究了显微组织、基体析出相、晶界析出相与晶界无沉淀析出带对材料强度与断裂韧性的影响,并分析了断裂机理。研究表明T7951二次时效产生的位错强化、细晶强化效应与基体内出现平衡η相导致的弱化作用之间的竞争机制导致材料强度较峰时效损失不大;晶界析出相的团聚粗化是造成二次时效7055铝合金断裂韧性提高的主因;7055铝合金室温拉伸断口表明断裂机理为韧脆混合型断裂,二次时效较峰时效表现出更强的韧性断裂特征。

The influences of microstructures, matrix precipitates, grain boundary precipitates and precipitate free zone on the strength and fracture toughness of 7055 aluminum alloy after peak aging and secondary T7951 heat treatments were studied through mechanical property tests, microstructures and fractography analyses. Results show that the strength of 7055-T7951 does not decrease dramatically compared with that of the peak aged material because of the competition between the softening effect of r/phase precipitating and the strengthening effects of dislocation and fine grains. The improvement of fracture toughness after secondary aging is mainly attributed to the aggregation and coarsening of grain boundary precipitates. Fractographic analyses indicate that the fracture mechanism is a mixture of both ductile and brittle features, but there are more ductile features in the secondary aged materials.