RRA过程中预时效时间对7A85铝合金组织性能的影响

系统研究了RRA处理过程预时效时间对7A85铝合金微观组织演变和性能的影响。利用Jmat-Pro软件计算了相变规律和TTT图,测试了硬度和拉伸性能指标,利用TEM表征了微观组织。结果表明,热力学平衡状态下,410 ℃开始析出MgZn₂相,体积分数达到9.5%左右;等温过程最先析出GP区,析出温度为室温~175 ℃,鼻尖温度在150 ℃左右;随着预时效时间的延长,硬度先升高后降低,20 h时达到峰值硬度192 HV;RRA处理过程,预时效时间为12 h时,屈服强度和抗拉强度达到峰值,分别为625 MPa和675 MPa;120 ℃保温20 h峰值时效状态下,η′-MgZn析出相尺寸在5~10 nm;预时效时间为12 h时,RRA处理后晶界处的Al-Zn-Mg-Cu四元相粒子呈不连续分布,尺寸在50~125 nm范围。

Influence of pre-aging time on microstructure and properties of 7 A85 aluminum alloy during RRA process

Influence of pre-aging time on microstructure and properties of the 7A85 aluminum alloy during RRA process was investigated. The thermodynamic equilibrium phase transformation and TTT curves were calculated by Jmat-Pro. The hardness and tensile properties were tested and microstructure was characterized by means of TEM. The results indicate that MgZn₂ phase begins to precipitate at 410 ℃ under thermodynamic equilibrium, volume fraction of which reaches about 9.5%. The GP zone is precipitated first during the isothermal process in the temperature range of room temperature to 175 ℃, and the nose tip temperature is about 150 ℃. With the extension of pre-aging time, the hardness first increases and then decreases, and reaches a peak hardness of 192 HV after aging for 20 h. The yield strength and tensile strength reach the peak value of 625 MPa and 675 MPa, respectively, when the pre-aging time is 20 h during the RRA process. During the heat preservation process at 120 ℃, under the peak aging state of 20 h, the size of the η′-MgZn precipitated phase is 5-10 nm. When the pre-aging time is 12 h, the Al-Zn-Mg-Cu quaternary phase particles with the size of 50-125 nm at the grain boundaries are discontinuously distributed after RRA treatment.