自然时效对7A99铝合金后续人工时效行为的影响

Effect of natural aging on subsequent artificial aging behavior of 7A99 aluminum alloy

采用扫描电镜、透射电镜、维氏硬度计、拉伸试验机、差示扫描量热仪等研究了7A99合金在室温自然时效不同时间及后续人工时效处理后的显微组织和力学性能。结果表明:自然时效对7A99铝合金硬化率影响较大,自然时效时间在0~96 h时,合金的时效硬化率较快,之后随自然时效时间的延长提升缓慢。淬火态、自然时效96 h和自然时效720 h的合金达到峰值硬度所需的时间分别是10、30和22 h。合金经不同时间自然时效后进行120℃×24 h人工时效,发现自然时效96 h后合金的强度存在明显下降,之后随着自然时效时间的延长强度开始回升。DSC分析计算出合金η′相的形成激活能在淬火态、自然时效96 h和自然时效720 h分别为106.3、120.2和114.4 kJ/mol。

Microstructure and mechanical properties of 7 A99 alloy after natural aging at room temperature for different time and subsequent artificial aging treatment were studied by means of scanning electron microscopy, transmission electron microscopy, Vickers hardness tester, tensile testing machine and differential scanning calorimeter. The results show that the natural aging has great influence on the hardening rate of the 7 A99 aluminum alloy. When the natural aging time is 0-96 h, the aging hardening rate of the alloy is faster, and then increases slowly with the increase of the natural aging time. The time required to reach the peak hardness of the alloy in quenched state, natural aged for 96 h and natural aged for 720 h is 10 h, 30 h and 22 h, respectively. After natural aging at room temperature for different time and subsequent artificial aging at 120 ℃ for 24 h, the strength of the alloy with natural aged for 96 h decreases significantly, and then with the increase of the natural aging time, the strength begins to rise. DSC results indicate that the formation activation energies of η′ phase of the alloy in quenched state, natural aged for 96 h and natural aged for 720 h are 106.3 kJ/mol, 120.2 kJ/mol and 114.4 kJ/mol, respectively.