High-temperature friction of 7075 aluminum alloy sheet during hot stamping

Aluminum alloys are lightweight materials widely used in the automobile industry because of their high specific strength. As the aluminum alloy with the highest strength at room temperature, 7075 aluminum alloy has great potential for usage in the manufacturing of structural parts. However, its formability at room temperature is poor and its springback is large. Although both good formability and high strength in aluminum alloys can be realized by hot forming, 7075 aluminum alloy has high susceptibility to adhesive wear, which means its tribological properties are poor during hot forming. Exploration of the influence of process parameters on the friction behavior and wear mechanism of 7075 aluminum alloy has great significance for the numerical simulation of the hot-stamping process and lubrication engineering. The high-temperature friction process of 7075 aluminum alloy during the actual hot forming–quenching integrated process was simulated by a self-made high-temperature strip friction tester. The upper and lower friction components were cooled and heated, respectively, to simulate the cooling and heating of the die (blank holder) in the actual hot-stamping process. The effects of the preheating temperature of the lower die, normal load, and sliding speed on the friction behavior and wear mechanism of 7075 aluminum alloy were analyzed. The results show that the friction coefficient of aluminum alloy increases with increase in the preheating temperature, and the wear mechanism changes from adhesive wear at 300 °C to adhesive, abrasive, and oxidative wear at 500 °C. The larger the normal load applied, the larger is the friction coefficient. The wear mechanism under different loads was determined to be adhesive wear with slight abrasive wear, with the degree of adhesive wear increasing with the increase in load. A high sliding speed leads to the formation of local oxides on the surface, which makes the friction coefficient decrease with an increase in the sliding speed. The main wear mechanisms are oxidative, abrasive, and adhesive wear when the sliding speed is 30 mm·s⁻¹.