Assessment of the impact of process parameters on the final material properties in forming of EN AW 7075 employing a simulated forming process

Abstract

The impacts of various thermo-mechanical process routes in forming of EN AW 7075 alloy on mechanical properties, microstructure and corrosion resistance were investigated. A simulated forming process of two very different conditions, i.e., T6 and W-Temper is the focus of the present study. Irrespective of soaking time and pre-deformation, specimens quenched in water exhibited superior mechanical properties compared to air-cooled ones. A shorter solution heat-treatment soaking time in the pre-deformed condition, i.e., T6-Temper, caused a drop in the elongation at fracture. Microstructural analysis revealed, regardless of pre-deformation and soaking time, a high fraction of fine η′ strengthening precipitates with stoichiometry close to MgZn upon artificial ageing in the specimens quenched in water. Mechanical properties and microstructural evolution indicate that pre-deformation of solution heat treated specimens before the ageing treatment, i.e., W-Temper, leads to dislocation multiplication and, eventually, further nucleation sites for precipitation. Thus, forming the W-Temper condition caused very similar resulting mechanical properties and microstructure compared to that of the T6 condition. However, W-Temper forming was found to be detrimental for stress corrosion cracking. Corrosion behaviour of air-cooled specimens was found to be very poor in general. Results obtained in the present work can facilitate the development of thermo-mechanical process routes for EN AW 7075 to eventually tailor mechanical properties, corrosion behaviour and microstructure.