新型高强韧低淬火敏感性Al-7.5Zn-1.65Mg-1.4Cu-0.12Zr合金

Novel Al-7.5Zn-1.65Mg-1.4Cu-0.12Zr alloys with high strength high toughness and low quench sensitivity

利用传统技术制备新型高强韧低淬火敏感性的Al-7.5Zn-1.65Mg-1.4Cu-0.12Zr合金,研究合金在制备加工以及不同热处理状态下的微观组织和性能。结果表明:该新型合金铸态组织具有枝晶间非平衡共晶相AlZnMgCu相对较少的特点,经过(440℃,12h)+(475℃,24h)双级均匀化处理、挤压变形和(475℃,50～120min)固溶处理后,组织均匀,固溶充分,除弥散分布的Al3Zr粒子外,仅残留有少量的Al7Cu2Fe相颗粒;经过单级、双级和三级时效处理,合金可以获得比较理想的组织和性能:T6态合金的抗拉强度590MPa,电导率20.4MS/m;经T7双级时效处理后,合金的抗拉强度、屈服强度、断后伸长率和电导率分别达到500～550MPa、460～520MPa、17.0%～17.3%和23.4～25.0MS/m;经三级时效处理后,合金的组织和力学性能兼顾了T6和T7两种制度的优势,与T6状态相比,在抗拉强度仅降低3%的情况下,电导率显著增加至23.1MS/m;合金具有低的淬火敏感性,室温水端淬试验测得的淬透深度可以达到120mm以上;新型合金具有优异的室温断裂韧性,其T6态的KIC值明显高于本研究同时制备的7150合金。

A novel Al-7.5Zn-1.65Mg-1.4Cu-0.12Zr alloy with high strength high toughness and low quench sensitivity was prepared by conventional ingot metallurgy.The microstructure and properties of the novel alloy under different processing and temper conditions were investigated.The results indicate that there are less coarse non-equilibrium AlZnMgCu phases in the as-cast alloy.After two-step homogenization（440 ℃, 12h＋475 ℃, 24h） followed by hot extrusion and solid-solution treatment at 475 ℃ for 50-120 min, the microstructure of the novel alloy is homogeneous with few undissolved phases existing in the matrix except a few indissolvable Al7Cu2Fe particles and dispersed Al3Zr phases.When one-step aging, two-step aging and three-step aging are performed, optimum microstructure and properties of the novel alloy are obtained.When T6 temper is performed, the ultimate tensile strength（UTS） and electrical conductivity values are 590 MPa and 20.4 MS/m, respectively.After T7 temper treatment, the UTS, tensile yield strength（TYS）, elongation and electrical conductivity values are 500-550 MPa, 460-520 MPa, 17.0%-17.3% and 23.4-25.0 MS/m, respectively.When three-step aging are performed, the alloy can obtain a good combination with T6 and T7 temper, the electrical conductivity is increased up to 23.1 MS/m and the UTS values is decreased only by 3% while in comparison with T6 temper.The novel alloy has low quench sensitivity, the quench sensitivity value of the alloy can reach more than 120 mm from the quenching end.The novel alloy also has better fracture toughness with higher KIC values than that of the 7150 alloy inT6 temper prepared by the same processing.