Mechanical Properties and Corrosion Behavior of Spray-Formed 7075 Alloy with One-Stage Aging
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JMEPEG https://doi.org/10.1007/s11665-019-03997-1
Mechanical Properties and Corrosion Behavior of Spray-Formed 7075 Alloy with One-Stage Aging Ruiming Su, Tong Liu, Yingdong Qu, Guang Bai, and Rongde Li (Submitted May 2, 2018; in revised form January 10, 2019) The mechanical properties, corrosion resistance and microstructure of the spray-formed 7075 alloy after one-stage aging treatments were studied by using a tensile tester, hardness tester, slow strain rate test, electrical test, intergranular corrosion test, electrochemical corrosion test, scanning electron microscope and transmission electron microscope. The results show that the strength and hardness of the alloy have double peaks with the one-stage aging treatments. With aging at 120 °C for 24 h (first peak), abundant tiny g¢ phases and g phases precipitate in the matrix. The tensile strength of the alloy increases to 760 MPa, and the elongation is 4.8%. After aging at 120 °C for 132 h (second peak), blocky g phases appear. The tensile strength and elongation of the alloy are 757 MPa and 5.9%, respectively. The grain boundary precipitates dissociate, and the precipitate-free zones are widened. The corrosion resistance of the alloy increases. Keywords
7075 alloy, aging, intergranular corrosion, mechanical properties, microstructure, spray forming, stress corrosion cracking
1. Introduction The 7075 (Al-Zn-Mg-Cu) alloy has been widely used in the aerospace industry due to its desirable specific mechanical properties (Ref 1-4). The tensile strengths of Al-Zn-Mg-Cu alloys using the spray forming method were improved to over 730 MPa in the 1990s (Ref 5-9). Studies on the 7075 alloy have been reported, but the reports focus on traditional forming and heat treatments, so the properties of the alloy may not be maximized (Ref 10-12). Yan et al. (Ref 13) found a double peak in the strength of AlZn-Mg-Cu alloys treated with one-stage overaging. YanÕs research was confirmed by Song et al. (Ref 14, 15), and the properties (especially at the second peak of the strength) of the traditional casting 7075 alloy after one-stage aging treatment were studied (Ref 16, 17). Some differences in the properties and microstructure of the alloy (e.g., solid solubility or grain size) between spray forming and traditional casting have been proven (Ref 18, 19). The properties and microstructure of spray-formed 7075 alloys are influenced by the aforementioned differences, and the relationships need to be studied. The corrosion sensitivity of 7075 alloys, especially intergranular corrosion (IGC) and stress corrosion cracking (SCC), increases after T6 treatment (Ref 20, 21). In some papers, the IGC and SCC behavior of 7075 alloys can be increased when subjected to a single-step aging by varying the aging times (Ref 22, 23). For corrosion resistance of spray-formed 7075 alloy, the influence of aging treatments is reported (Ref 24-26). Ruiming Su, Tong Liu, Yingdong Qu, Guang Bai, and Rongde Li, School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110870, Peop
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