Hot tensile deformation behavior of twin roll casted 7075 aluminum alloy

Abstract

High temperature deformation behavior of the 7075 aluminum alloy sheets fabricated by twin roll casting and rolling was investigated by hot tensile tests at different temperatures from 350 to 500°C and various initial strain rates from 1×10 -3 to 1×10 -2 s -1. The results show that flow stress increased with increasing initial strain rate and decreasing deformation temperature. A large elongation of 200% was obtained at relatively high strain rate of 5×10 -3 s -1 at 450°C. It is closely related with the grain boundary sliding at elevated temperature attributed to the recrystallized fine grains and the large volume fraction of high-angle grain boundaries. The fracture transformation mechanism changes from ductile transgranular fracture to ductile intergranular fracture due to the recrystallized fine grains at high temperature. High density and uniform cavities observed in large elongation samples at high temperature reveals the contribution of grain boundary sliding. Necking-controlled failure mode was characterized by rare cavities with low elongation.

Effects of Temperature and Strain Rate on the Fracture Behaviors of an Al-Zn-Mg-Cu Alloy

“…As a general trend, fracture strain rises with the elevation of temperature at each strain rate in Figure 2 . It can be found that flow stress rises with the increasing of strain rate at given temperature, as depicted in Figure 3 , mainly due to the enhanced deformation storage energy [ 5 ].…”

“…However, high contents of alloying elements may simultaneously weaken the hot workability of the alloy [ 1 ]. It has been widely acknowledged that deformation mechanisms of work hardening (WH) [ 2 , 3 ], dynamic recrystallization (DRX) [ 4 , 5 ], and dynamic recovery (DRV) [ 6 , 7 ] can result in different deformation behavior of Al-Zn-Mg-Cu alloy. Therefore, the problem of how to enhance the mechanical properties and optimize the formability of Al-Zn-Mg-Cu alloy has become a research hotspot in recent years, and some researches have been made to explore its hot deformation behaviors at quasi-static strain rate [ 8 , 9 , 10 ].…”

“…Heretofore, investigating microstructural evolution would be an effective method to explore the underlying mechanism of the macroscopic fracture [ 13 , 14 , 15 ]. Wang, L. et al [ 5 ] found that recrystallized grains and a high proportion of high-angle grain boundaries at high temperature can lead to grain boundary sliding (GBS), which results in a large elongation of 200% of twin roll casted (TRC) 7075 aluminum alloy at strain rate of 5 × 10 −3 s −1 and temperature of 450 °C. El-Magd, E. et al [ 16 ] asserted that under tensile loading, nucleation, growth, and the coalescence of microvoids dominates the failure of AA7075 alloy.…”

Aluminum Alloys Behavior during Forming

“…At high temperatures from 350 to 500°C and strain rates from 1 × 10 −3 to 1 × 10 −2 s −1 , hot tensile test was performed. The results showed that by increasing the strain rate and decreasing deformation temperature, flow stress was increased [9]. Similarly, three aluminum alloys containing different silicon contents were studied at a temperature range of 573-773 K with strain rates of 0.01, 0.1, 1 and 5 s −1 [10].…”

Effect of Pre-Aging Treatment on Bake-Hardenability of Al-8.0Zn-2.5Mg-2.0Cu Alloy Sheet Fabricated by Twin-Roll Casting Process

“…또한 용체화 처리 후 자연시효된 7075 합금을 소부경화처리할 경우, 불균일하고 조대한 시효 석출상 (MgZn 2 )이 형성되어 강도 상승을 저해하는 것으로 보고되 었다 [13]. 또한 기존 차체용으로 사용되는 Al-Mg-Si계 합 금의 경우에는 예비시효(Pre-aging) [3,15,16] 및 예비변형 정도로 매우 크기 때문에 미세한 주조 조직을 얻을 수 있으며, 정출상의 크기를 미세화할 수 있는 장점 이 있다[19,20]. 전기로를 사용하여 720 o C에서 Al, Zn C에서 1시간 열처리 후, 두께 3.0 mm까지 열간압연을 행하였다.…”