Study on the effect of enhanced magnesium and copper contents on microstructure and property of Al-Zn-Mg-Cu alloys with high zinc element content during fabrication processes

Abstract

Magnesium and copper elements can significantly influence precipitation characteristics, and furtherly change the property of final products in Al-Zn-Mg-Cu alloys. The current work chose a high Zn-containing Al-Zn-Mg-Cu alloy with synchronously enhanced magnesium and copper contents. Related microstructure and property were thoroughly investigated during the preparation process. The results showed that the solidification phase in as-cast microstructures was mainly AlZnMgCu. At the same time, the amount of it was enhanced with the increased content of magnesium and copper elements. After homogenization by 400°C/10h+472°C/56h, the eutectic ones dissolved into the α(Al), and only a sporadically distributed Fe-rich phase was observed. Mg(Zn, Cu, Al)2 phases with dense distribution and small size existed in extruded microstructure, most of them were re-dissolved in the α(Al) by solution treated with a regime of 472°C/4h. After single aged by 120°C/24h, the strength possessed an incremental trend with the increased content of magnesium and copper elements, while the elongation and electrical conductivity showed an opposite trend. MMC alloy possessed the largest fracture toughness value. When the alloys were aged by double-stage regimes, the strength, and electrical conductivity had incremental trends, while elongation possessed a decremental trend, as same as the single-aging ones.