Improved solid solution treatment of two different Cu-containing Al-Zn-Mg-Cu alloys
Journal
Materials Science and Engineering: A
Journal Volume
931
Start Page
148157
ISSN
0921-5093
Date Issued
2025-06
Author(s)
Tz-En Chang
Ting-Jung Hsiao
Shu-Cheng Liang
Cheng-Ling Tai
Shih-Yuan Lu
Yu-Jen You
Chu-Jen Chen
Yo-Lun Yang
Chih-Yuan Chen
Jer-Ren Yang
Abstract
Multi-stage solid solution treatments (SSTs) for two 7075 aluminum alloys, Al-5.98Zn-2.86Mg-1.61Cu, wt. % (denoted as 7075-LCu) and Al-5.91Zn-2.83Mg-1.98Cu, wt.% (denoted as 7075-HCu), have been investigated. Due to their different Cu contents, the two alloys possess different volume fractions of the primary second phases in the as-received plates. In this work, X-ray diffraction (XRD) was employed to identify the second phases in the alloys and differential scanning calorimetry (DSC) to characterize the melting points of the second phases. To verify the types of second phases in specimens after each stage of solution treatment with the ageing treatments, electron probe micro analysis (EPMA) was also employed. The main micro-scale sized second phases in two as-received alloys are the η phase and the S phase; their nominal compositions are Mg(Zn, Al, Cu)2 and Al2CuMg, respectively. Therefore, multi-stage SSTs were designed respectively for these two alloys. In these SSTs, the temperature of each stage was set slightly lower than the melting points of the corresponding second phases (η phase and S phase) in an attempt to achieve complete solid solutioning in the matrix without incipient melting. After the SSTs, aging processes with natural aging (NA) and artificial aging (AA) were applied. Under the newly designed multi-stage SSTs with (NA + AA), both the strength and elongation of these two alloys were significantly improved as compared to their counterparts treated by conventional single-stage SST with (NA + AA). The results showed that the elongation of 7075-LCu improved from 11.8 % (single-stage SST with NA + AA) to 15.0 % (multi-stage SST with NA + AA), a 27 % increase, and the corresponding ultimate strength improved from 597 MPa to 606 MPa. Similarly, the elongation of 7075-HCu improved from 12.6 % (single-stage SST with NA + AA) to 15.2 % (multi-stage SST with NA + AA), a 20 % improvement, and the corresponding ultimate strength improved from 596 MPa to 613 MPa. The effects of the elimination of second phases in the aluminum matrix without incipient melting on the properties of subsequent peak-aging treatments are discussed.
Subjects
Al-Zn-Mg-Cu alloy
Cu addition
Differential scanning calorimetry (DSC)
Electron probe micro analysis (EPMA)
Incipient melting
Second phase
Solid solution treatment
Transmission electron microscopy (TEM)
X-ray diffraction (XRD)
SDGs
Publisher
Elsevier BV
Type
journal article