Reversion of natural ageing and restoration of quick bake-hardening response in Al-Zn-Mg-Cu alloy

• 作者: Chunhui Liu Zhuangzhuang Feng Peipei Ma Yihui Zhou Guohui Li Lihua Zhan
• 来源期刊: 材料科学技术（英文版）
• 年，卷（期）: 2021,（36）
• 页码范围: 88-94
• 页数: 7页
• 语种: 英文

摘要

The high-strength Al-Zn-Mg-Cu alloy provides much better dent resistance and weight-reduction poten-tial compared to the conventional Al alloys used for the automobile body panels.However,natural age-ing (NA) significantly reduces the formability of Al-Zn-Mg-Cu alloy.The reversion of natural ageing has been systematically investigated by hardness test,tensile test,differential scanning calorimetry (DSC) and transmission electron microscopy (TEM).Substantial reversion of natural ageing and thus hardness de-crease occurs immediately upon thermal treatment at 120-210 ℃ in an Al-Zn-Mg-Cu alloy.Although the hardness of the most reverted state decreases with increasing temperature,the lowest hardness is still higher than the as-quenched state by 30HV.As revealed by the complementary DSC and TEM observa-tions,this is ascribed to the synchronization of the dissolution and the re-precipitation of the solutes in the NA clusters during reversion ageing.Reversion at 180-210 ℃ for less than 30 s leads to a hardness decline of 40HV.The hardening kinetics during NA after reversion is slower than that during first-time NA due to the reduced vacancy concentration.Artificial ageing at 180 ℃ for 30 min after secondary NA of less than 24 h induces intensive precipitation of plate-like pre-ηphases and a giant strength increase of 188-204 MPa.Potential use of high strength Al-Zn-Mg-Cu alloy in automobile body panels could be realized by appropriate reversion treatment improving the formability and the quick bake hardening re-sponse.