Effect of pre-aging and precipitation behavior on mechanical properties of 7055 aluminum alloy processed by hot-forming quenching

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 sys-tematically studied using High Resolution Transmission Electron Microscopy-Selected Area Electron Diffraction (HRTEM-SAED). The results revealed the precipitation nature of eta phase in 7055 aluminum alloys is that GP zone I evolves into GP zone II, on which eta' phases directly nucleate and multiply, resulting in the transformation from eta' phases into eta phases. By comparing the three processes, it is found that HFQ + PA + SB has high-density and finely distributed eta' 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 eta' 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.

Automated summary

Hot-forming Quenching (HFQ) can significantly alter the microstructure of high-strength aluminum alloys for car body sheet and achieve desired performance through effective control. Three designed processes, HFQ + Natural Aging (NA) + Simulate Baking (SB), HFQ + Pre-aging (PA) + SB and HFQ + Peak-aging (T6), were systematically studied using HRTEM-SAED to understand the evolution of precipitated phases. The results showed that HFQ + PA + SB had high-density and finely distributed eta' phases, with small and discontinuously distributed grain boundary precipitates. Adjusting the pre-aging temperature and time provided ample nucleation sites for precipitation during the baking stage, ensuring the formation of eta' phases with high quantity density. The end product exhibited a tensile strength of 660.1 MPa and a yield strength of 639.4 MPa, making it a promising material for future car body applications.