The high-strength Al-Zn-Mg-Cu alloy provides much better dent resistance and weight-reduction potential compared to the conventional Al alloys used for the automobile body panels.However,natural ageing(NA)significantl...The high-strength Al-Zn-Mg-Cu alloy provides much better dent resistance and weight-reduction potential compared to the conventional Al alloys used for the automobile body panels.However,natural ageing(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 decrease 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 30 HV.As revealed by the complementary DSC and TEM observations,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 40 HV.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 response.展开更多
For a series of Al-0.34／%Mg-1.05／%Si-0.08／%Cu alloys, the effects of pre-treatment on natural aging, bake hardening response and plasticity were investigated using Vickers hardness test and tensile test. Differenti...For a series of Al-0.34／%Mg-1.05／%Si-0.08／%Cu alloys, the effects of pre-treatment on natural aging, bake hardening response and plasticity were investigated using Vickers hardness test and tensile test. Differential scanning calorimetry （DSC） analysis was conducted to reveal corresponding precipitation mechanisms. The results showed that pre-straining and pre-aging alone couldn＇t completely suppress natural aging and improve bake hardening response simultaneously. The sensitivity of the pre-straining and pre-aging on the mechanical properties was evaluated. It was found that pre-aging was the main factor which greatly improved bake hardening response and pre-treatment had a weak influence on plasticity in pre-treated samples. DSC analysis showed that the dissolution trough of clusters disappeared in pre-treated samples, both β”and β＇ precipitation peak shifted to lower temperature and were reduced in pre-strained and pre-aged samples. It was concluded that the formation of Mg/Si clusters was replaced by the accelerated precipitation ofβ” andβ＇ phases, which caused the suppression of natural aging and the improvement of bake hardening response （BHR）.展开更多
基金financial support from National Natural Science Foundation of China(Nos.U2032117,51675538,11872380)the National Key R&D Program of China(No.2017YFB0306300)+3 种基金Natural Science Foundation of Hunan Province(No.2018JJ3655)National Science and Technology Major Project(No.2017ZX04005001)the Fundamental Research Funds for the Central Universities of Central South University(2021zzts0638)the Innovation fund of National commercial aircraft manufacturing engineering technology centre(No.COMAC-SFGS-2019-4284)。
文摘The high-strength Al-Zn-Mg-Cu alloy provides much better dent resistance and weight-reduction potential compared to the conventional Al alloys used for the automobile body panels.However,natural ageing(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 decrease 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 30 HV.As revealed by the complementary DSC and TEM observations,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 40 HV.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 response.
基金supported by the Fundamental Research Fund for the Central Universities(No.CDJZR10130018)the Chongqing Science and Technology Commission (No.2011GZ0039)
文摘For a series of Al-0.34／%Mg-1.05／%Si-0.08／%Cu alloys, the effects of pre-treatment on natural aging, bake hardening response and plasticity were investigated using Vickers hardness test and tensile test. Differential scanning calorimetry （DSC） analysis was conducted to reveal corresponding precipitation mechanisms. The results showed that pre-straining and pre-aging alone couldn＇t completely suppress natural aging and improve bake hardening response simultaneously. The sensitivity of the pre-straining and pre-aging on the mechanical properties was evaluated. It was found that pre-aging was the main factor which greatly improved bake hardening response and pre-treatment had a weak influence on plasticity in pre-treated samples. DSC analysis showed that the dissolution trough of clusters disappeared in pre-treated samples, both β”and β＇ precipitation peak shifted to lower temperature and were reduced in pre-strained and pre-aged samples. It was concluded that the formation of Mg/Si clusters was replaced by the accelerated precipitation ofβ” andβ＇ phases, which caused the suppression of natural aging and the improvement of bake hardening response （BHR）.
