Thermomechanical pretreatment of Al-Zn-Mg-Cu alloy to improve formability and performance during creep-age forming

Thermomechanical treatment is often conducted to improve the formability and performance of high-strength aluminum alloys simultaneously. This paper presents an improved creep-age forming (CAF) processing technology that combines thermomechanical pretreatment and CAF. The proposed processing technique is expected to enhance the forming efficiency and comprehensive properties of Al-Zn-Mg-Cu alloys subjected to CAF. Creepaging behavior and properties of the 7150 aluminum alloy undergoing retrogression and re-aging (RRA) with 3 % pre-strain treatment was experimentally investigated in this study. Results obtained reveal greater creep deformation in thermomechanically pretreated samples than in those pretreated using RRA or 3 % pre-strain exclusively. Mechanical properties, electrical conductivity, and exfoliation corrosion of creep-aged samples with thermomechanical pretreatment were closely match those of the traditional RRA-treated sample. Microstructure observation discovered eta(2) phase in the creep-aged RRA pretreated sample in addition to conventional GP /eta' phase, eta phase and coarse and discrete grain-boundary precipitates. Low concentration of solutes in matrix in RRA pretreated sample impeded dislocation motion less and pre-strain-induced dislocations increased the creep strain significantly. Moreover, hardening effect of eta(2) phase and dislocation hardening compensated the strength loss due to precipitation coarsening. The proposed thermomechanical pretreatment process provides an appropriate initial temper for CAF of Al-Zn-Mg-Cu alloys, thereby improving the creep formability and comprehensive properties remarkably. The findings of this study could aid in the development of CAF technology for Al-Zn-Mg-Cu alloys, especially in terms of manufacturing aviation components.