Abstract
Hot-forming Quenching (HFQ) can lead to significant changes in microstructure of high-strength aluminum alloys for car body sheet. Furthermore, through effective control, desired performance of the alloys can be achieved. Three designed processes, HFQ + Natural Aging (NA) + Simulate Baking (SB), HFQ + Pre-aging (PA) + SB and HFQ + Peak-aging (T6) were applied in this work, and the evolution of precipitated phases was systematically studied using High Resolution Transmission Electron Microscopy-Selected Area Electron Diffraction (HRTEM-SAED). The results revealed the precipitation nature of η phase in 7055 aluminum alloys is that GP zone I evolves into GP zone II, on which η’ phases directly nucleate and multiply, resulting in the transformation from η’ phases into η phases. By comparing the three processes, it is found that HFQ + PA + SB has high-density and finely distributed η’ phases, and grain boundary precipitates are small and discontinuously distributed. By adjusting the pre-aging temperature and time, it can provides a large amount of precipitation nucleation basis for the baking stage and ensure that η’ phase formation with high quantity density. The end product has a tensile strength of 660.1 MPa and a yield strength of 639.4 MPa, which is the most promising sheet material for future car body application.