Microstructure, mechanical properties, and strengthening mechanisms of ultra-high strength Al-Zn-Mg-Cu alloy prepared by continuous extrusion forming process

In recent years, the strategy of obtaining ultra-high strength bulk Al-Zn-Mg-Cu alloys materials through implementing severe plastic deformation (SPD) has emerged as the prominent trend in structural lightweight development in aerospace and transportation fields. However, the inherent poor formability makes the SPD process of high-alloying Al-Zn-Mg-Cu alloys a great challenge. In the present work, a continuous SPD process named the Conform, utilizing a rotational speed of 4 rpm and a mold preheating temperature of 300 °C, was performed on the high-alloying 7055 Al alloy and prepared rod materials with excellent mechanical properties. The results indicated that violent shear deformation accompanied by rapid temperature rise contributes to the specific grain refinement mechanism of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). The grain configuration formed by this cooperative mechanism is advantageous for the alloy's compatible deformation capability. As a result, a synergistic improvement in the strength and ductility of the Conformed 7055 Al alloy was obtained. Additionally, the strengthening mechanisms induced by the Conform process were quantitatively calculated, revealing that solid solution strengthening and dislocation strengthening were the primary reasons for the enhanced strength of processed alloys.