Effect of Artificial Aging on the Mechanical and Fatigue Properties of the Hot-Stamped 6022 Aluminum Alloy

The mechanical and fatigue properties of the 6022 aluminum alloy were investigated experimentally using U-bend samples fabricated through the hot-stamping process. The hot-stamping process was carried out at 550 °C before conducting artificial aging under several conditions. The alloy obtained via the hot-stamping process exhibited a lower degree of internal strain and a higher formability with a lower spring back compared with that obtained via the cold-stamping process. As the hot-stamping process was conducted at a temperature close to the solution temperature of the 6022 alloy, precipitation hardening occurred after artificial aging. The hardness of the hot-stamped 6022 alloy increased with increasing the aging temperature, and the high hardness was detected at 170 °C for 4 and 12 h due to the different strengthening mechanisms, namely dislocations and Mg2Si base precipitates. Like the results of the hardness, a high ultimate tensile strength and a high fatigue strength were obtained for the hot-stamped 6022 alloy after artificial aging at 170 °C for 4 h. The tensile strength is more than 35% higher than that of the cold-stamped sample. Although a high tensile strength was obtained after the aging process, the resistance to crack growth was not very high. This was attributed to the high crack driving force caused by the weak crack closure and low strain energy of the aged 6022 alloy. The failure characteristics of the hot-stamped 6022 samples were investigated via several experimental approaches to understand in detail the material properties of the aged 6022 alloy.