Hot deformation and microstructural evolution of ultrasonically fabricated as-cast Al-7.3Zn-2.2Mg-2Cu alloy

Abstract

Al-7.3Zn-2.2 Mg-2Cu alloy is known for its high strength, achieved because of higher alloying concentration. However, the higher alloying concentration presents challenges during the hot deformation process. Nevertheless, hot deformation proves to be an effective method for optimizing the microstructural and mechanical properties of the material. The research presented in the study focuses on investigating the hot working response of an ultrasonically fabricated age-hardening as-cast Al-7.3Zn-2.2 Mg-2Cu alloy. The objective is to observe the attainment of a uniform and dendrite-free microstructure after a single-step hot compression. The flow stress of the deformed specimens showed a notable increase as the temperature and deformation time decreased. This increase in stress was influenced by various factors, including deformation variables and precipitate size. The accurate prediction of the hot deformation behaviour was achieved by combining the constitutive equations and a workability map. The 3-dimensional workability map revealed a gradually increasing power dissipation efficiency (PDE) from 40% to 50% with increasing strain. At the end of 50% compression, four specific optimum working regions (PDE > 40%) were identified. Through detailed microstructural analysis, the best region for hot forging of ultrasonically mixed as-cast alloy for chemical homogeneity and upgraded property is obtained in the range of (350–450 °C) & (0.1–0.001 s−1). The highest extent of recrystallization (73%) was exhibited after deformation at 450 °C-0.001 s−1. The mechanism of dynamic softening during deformation is observed due to DRV, CDRX, and PSN. The microstructural response in 0.1–0.001 s−1 and 350–450 °C indicated dynamic recrystallization, whereas strained and non-working zone was observed at low deformation temperatures (≤350 °C).