Design of the multi-stage quenching process for 7050 aluminum alloy

• Single-stage quenching tests were conducted based on the end quenching equipment.
• Multi-stage quenching tests are reasonably designed from the experimental results.
• Coupling control of the cooling rate and the residual stress has been achieved.

In order to attain good hardenability in the single-stage quenching process of Al–Zn–Mg–Cu alloys, rapid cooling rate is often desirable. But this would inevitably increase the residual stress. Therefore, the aim of this study is to achieve coupling control of the cooling rate and the residual stress by using the multi-stage quenching process. First, a series of single-stage quenching tests were conducted based on the end quenching equipment. Then in the double-stage quenching tests, a higher cooling rate was obtained comparing to the single-stage quenching. Based on this discovery, three kinds of multi-stage quenching processes were designed based on the experimental results of the single-stage quenching tests. The mechanism of the multi-stage quenching has been analyzed by comparing the cooling curves, the microstructure, the hardening depth, and the maximum residual stress. Furthermore the optimal multi-stage quenching process for 7050 aluminum alloy plate was obtained.