The 7000 series aluminum alloys are high-strength materials widely utilized for weight reduction in transportation equipment and aerospace applications. Among these, the AA7075 alloy is notable for its exceptional strength, making it increasingly attractive for use in aircraft components, sporting goods, and other demanding fields. However, its high resistance to deformation often results in surface defects, such as tearing on product surfaces, and contributes to reduced tool life, thereby limiting productivity. The primary factors contributing to short tool life include the inherently high strength and adhesive wear caused by alloying elements, such as zinc. Die coatings have been employed to mitigate adhesion. However, the correlation between coating strength and service life remains unclear. To address this, the present study focused on optimizing die materials to minimize adhesion during forming, with the goal of enhancing the extrusion productivity of AA7075 alloy. The application of cobalt-chromium-molybdenum (CoCrMo) alloy, recognized for its superior wear resistance, was proposed as an innovative die tool material. Hot friction tests and extrusion trials demonstrated that CoCrMo alloy significantly reduced the adhesion of magnesium (Mg), Zn, and copper (Cu)—key alloying elements in AA7075—when compared with the conventional AISI H13 die material. Furthermore, the surface roughness of the products were more uniform. The improved performance is attributed to the formation of a stable oxide film at high temperatures, which effectively suppresses adhesion and enhances the surface quality of the final products.
Funazuka et al. (Thu,) studied this question.