四种Al-Zn-Mg-Cu合金淬火敏感性研究

Quench sensitivity of four Al-Zn-Mg-Cu aluminum alloys

摘要:

采用第一性原理在JMatPro7.0软件的Al基数据库完成四种Al-Zn-Mg-Cu合金时间-温度-转变(TTT)曲线和CCT曲线计算。结论是: 7055合金的主合金元素总量及Cu含量最高,TTT曲线和CCT曲线在左上方；7085合金的Cu含量最低且Zn/Mg比值最高,TTT曲线和CCT曲线在右下方,平衡相析出的孕育期最长,开始析出温度和鼻尖温度最低,合金的淬火敏感性最低；7075合金Zn/Mg比值最小且晶内存在非共格的E(Al₁₈Cr₂Mg₃)相,合金的淬火敏感性最高。实验研究表明与冷却速率960℃/s处相比,冷却速率1.8℃/s处7075、7055、7050和7085四种合金淬火态的电导率差值和时效态的硬度下降率均减小,硬度下降率分别为35.5%、19%、13.8%和9.5%,此处四个合金固溶体的晶格常数及淬火析出相的尺寸及面积分数依次减小,因此其淬火敏感性依次降低。

Abstract:

The time-temperature-transformation(TTT) curves and CCT curves of four Al-Zn-Mg-Cu alloys were completed in the Al-based database of software JMatPro7.0 with the first principles. To conclude, for 7055 alloy with the highest gross amount of main alloying elements and highest Cu element content, TTT and CCT curves were at the top left. For 7085 alloy with the lowest Cu element content and highest Zn/Mg ratio, TTT and CCT curves were at the bottom right, thus the incubation of equilibrium phase precipitation was the longest, start precipitation temperature and the nose temperature were the lowest, and therefore the quench sensitivity was the lowest. For 7075 alloy with the lowest Zn/Mg ratio and the incoherent E (Al₁₈Cr₂Mg₃) phase within grains, the quench sensitivity was the highest. The results show that compared with the conductivity of as-quenched and hardness as-aged at 960℃/s, the conductivity difference and hardness drop rates for 7075,7055,7050,7085 four alloys cooled at 1.8℃/s were decreased and the hardness drop rates were 35.5%, 19%, 13.8% and 9.5% respectively. The lattice constant and the size and area fraction of the quench-induced phases for the four alloys cooled at 1.8℃/s reduced, and thus the quench sensitivity decreased.