Improved creep forming efficiency and retained performance via a novel two-stage creep aging process of Al–Zn–Mg–Cu alloys

Abstract

A novel two-stage creep aging forming (CAF) process with an elevated temperature followed by peak-aging temperature was developed to notably improve the creep forming efficiency and to achieve a favorable combination of strength and corrosion resistance in an Al–Zn–Mg–Cu alloy. Compared with traditional single-stage creep aging, the proposed two-stage creep aging (TSCA) halved the formation time while doubling the creep deformation without sacrificing strength. This specific aging procedure can manipulate precipitation evolution, thus effectively affecting the deformation and performance of the studied alloy. The creep responses, properties, microstructure evolution and their relationship of 7B50 aluminum alloy subjected to TSCA were investigated and discussed through creep and property tests, transmission electron microscopy, and differential scanning calorimetry. Both precipitate dissolution and high temperatures were beneficial for the exceptional creep response in the high-temperature creep aging process, whereas the re-precipitation of new Guinier–Preston (GP) zones in the low-temperature stage could practically counteract the strength loss at elevated temperatures. Moreover, the corrosion resistance was persistently enhanced throughout the process owing to coarse and discrete grain boundary precipitates. These results are of significance in the development of CAF technology for Al–Zn–Mg–Cu alloy components.