Effect of Cu Additions on the Evolution of Eta-prime Precipitates in Aged AA 7075 Al–Zn–Mg–Cu Alloys

Abstract

In the present study, after solid solution treatment, four different artificial aging treatments (100, 120, 140 and 160 °C) were performed on Al-5.98Zn-2.86Mg-1.61Cu (wt.%) alloy, denoted as 7075-LCu, and Al-5.91Zn-2.83Mg-1.98Cu (wt.%) alloy, denoted as 7075-HCu. Peak aging conditions were determined for each aging temperature at various hold time intervals of up to 24 h. It was found that both alloys possessed the optimal strengths after artificial aging at 120 °C for 24 h. Under this condition, the ultimate tensile strengths (UTSs) were 618 MPa (7075-LCu) and 623 MPa (7075-HCu), respectively. Moreover, a method was used to calculate the average sizes and number density of the major strengthening precipitates, η′, under peak aging conditions in these two alloys from transmission electron microscopy (TEM) images and electron energy loss spectroscopy (EELS). The above results indicated that for the 7075-LCu and 7075-HCu samples with the optimal UTS strengths, the former possessed an average thickness of 2.15 nm, and a number density of 3.27 × 1017 cm−3; the latter, 2.04 nm and 3.52 × 1017 cm−3.

Research Status and Prospective Properties of the Al-Zn-Mg-Cu Series Aluminum Alloys

“…An increase in Zn and Mg elements can improve the yield strength of the alloy. Cu provides a certain contribution to the strength of the alloy that improves the corrosion resistance [1,2]. But there is a threshold for each element, for which the difference is obvious for different components of the alloy.…”

Phase Composition and Microstructure of Cast Al-6%Mg-2%Ca-2%Zn Alloy with Fe and Si Additions

“…This solubility sharply decreases with cooling, resulting in the precipitation of metastable precursors of MgZn 2 and/or Al 2 Mg 3 Zn 3 phases. For example, this effect was successful in AA7xxx alloys based on the Al-Zn-Mg system [25][26][27][28][29].…”