Investigation on microstructure and mechanical properties of Al-Zn-Mg-Cu alloys with various Zn/Mg ratios

The effects of Zn/Mg ratios on microstructure and mechanical properties of Al-Zn-Mg-Cu alloys aged at 150 degrees C have been investigated by using tensile tests, optical metallography, scanning electron microscopy, transmission electron microscopy and atom probe tomography analyses. With increasing Zn/Mg ratios, the ageing process is significantly accelerated and the time to peak ageing is reduced. T' phase predominates in alloys of lower Zn/Mg ratios while eta' phase predominates in alloys with a Zn/Mg ratio over 2.86. Co-existence of T' phase and eta' phase with a large number density is beneficial to the high strength of alloys. Such precipitates together with narrow precipitate free zones cause a brittle intergranular fracture. A strength model has been established to predict the co-strengthening effect of T' phase and eta' phase in Al-Zn-Mg-Cu alloys, including the factors of the grain boundary, solid solution and precipitation. (C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

The study investigated the effects of Zn/Mg ratios on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloys aged at 150 degrees C. It was found that an increase in Zn/Mg ratios significantly accelerates the aging process, with the co-existence of T' phase and eta' phase beneficial to the high strength of the alloys.