Enhanced mechanical properties and corrosion resistance of 7055 aluminum alloy through variable-rate non-isothermal aging

Abstract

The effect of variable-rate non-isothermal aging (VR-NIA) on the properties of 7055 aluminum alloy was investigated by hardness, electrical conductivity, tensile tests and immersion corrosion, stress corrosion and electrochemical corrosion experiments. A four-stage VR-NIA process is proposed and applied to 7055 alloy, and a good combination of mechanical properties and corrosion resistance can be obtained in a relatively short time. TEM and HRTEM images show that GPⅠ zones, GPⅡ zones and η' phases are formed during the heating process of 100→180 °C, which enhances the mechanical properties; in the process of 180→210→180 °C, GPⅠ zones, part of the small-sized GPⅡ zones and η' phases are redissolved into the matrix, while part of η' phases grows. Meanwhile, the grain boundary precipitates (GBPs) change from continuous to discontinuous, forming the proper width of the precipitate free zone (PFZ), which greatly improves the electrical conductivity and corrosion resistance. In the cooling process of 180→100 °C, "secondary precipitation" of the GPⅠ zones occurs, and the η' phases grow up, with a small part transforming into the η phases, but no remarkable coarsening occurs. During the process of VR-NIA, the content of Zn, Mg, and Cu elements in GBPs is increasing continuously.