Impact of Aging Treatment on Microstructure and Performance of Al-Zn-Mg-Cu Alloy Thin Sheets

Abstract

Al-Zn-Mg-Cu alloy, recognized for its heat-treatable and super-high strength, is a pivotal material for critical structural components in aviation. Consequently, grasping the intricate relationship between heat treatment processes and the microstructural characteristics and properties of the Al-Zn-Mg-Cu alloy is of paramount practical significance. This study encompasses a spectrum of heat treatment methodologies, delving into the diverse effects of distinct aging treatments on the microstructure and performance of thin Al-Zn-Mg-Cu alloy sheets. The findings illuminate that short natural aging treatments bestow heightened strength and hardness upon the alloy, albeit at the expense of ductility. Nevertheless, the alloy retains commendable malleability, enabling significant cold deformation. In contrast, artificial aging markedly elevates the alloy’s strength and hardness, albeit concurrently inducing a precipitous decline in ductility, thereby attenuating the alloy’s cold formability.

Research on Alloy Design and Process Optimization of Al–Mg–Zn-Cu-Based Aluminum Alloy Sheets for Automobiles with Secured Formability and Bake-Hardenability

“…were performed under conditions of 470 °C/2 h of solution temperature and 120 °C of artificial aging, and, in order to learn more about the formation tendency of the GP zone, which is the nucleation site of the η' phase, the region between 0 and 1 h was enlarged and is shown in Figure 1. The heat treatment conditions used in the calculation were the commonly performed T6 heat treatment conditions for Al-Mg-Zn-Cu-based aluminum alloys [14][15][16]. It was confirmed that the GP zone was formed rapidly at a temperature of 120 °C, peaked within about 30 min of aging, and then transformed to η' and decreased.…”

“…Therefore, currently, Al-Mg-Si alloys are mainly used, which have high formability and relatively low yield strength, even after natural aging, and excellent bakehardening characteristics after paint bake treatment. On the other hand, in the case of Al-Mg-Zn-Cu alloys, it is generally known that maximum strength is obtained through artificial aging at a temperature of around 120 • C [14][15][16], and excellent mechanical properties of over 500 MPa can be secured [17,18]. But, despite their high-strength characteristics, they are not preferred due to increased yield strength due to natural aging, increased sheet-forming pressure, and reduced mechanical properties due to grain coarsening at bake-hardening temperatures [7,[19][20][21].…”