Investigation on Yield Behavior of 7075-T6 Aluminum Alloy at Elevated Temperatures

Jianping Lin,Yong Hou,Jiajie Chen,Xingyu Bao,Zhimin Tao,Xinlei Qu,Junying Min

doi:10.1186/s10033-020-00494-8

Abstract

Aluminum alloys have drawn considerable attention in the area of automotive lightweight. High strength aluminum alloys are usually deformed at elevated temperatures due to their poor formability at room temperature. In this work, the yield behavior of 7075 aluminum alloy in T6 temper (AA7075-T6) within the temperature ranging from 25 °C to 230 °C was investigated. Uniaxial and biaxial tensile tests with the aid of induction heating system were performed to determine the stress vs. strain curves and the yield loci of AA7075-T6 at elevated temperatures, respectively. Von Mises, Hill48 and Yld2000-2d yield criteria were applied to predicting yield loci which were compared with experimentally measured yield loci of the AA7075-T6. Results show that yield stress corresponding to the same equivalent plastic strain decreases with increasing temperature within the investigated temperature range and the shape of yield loci evolves nearly negligibly. The experimental yield locus expands with an increase of equivalent plastic strain at the same temperature and the work hardening rate of AA7075-T6 exhibits obvious stress-state-dependency. The non-quadratic Yld2000-2d yield criterion describes the yield surfaces of AA7075-T6 more accurately than the quadratic von Mises and Hill48 yield criteria, and an exponent of 14 in the Yld2000-2d yield function gives the optimal predictions for the AA7075-T6 at all investigated temperatures.

Highlights

Lightweight materials, e.g., advanced high strength steels and aluminum alloys, have been identified as a key priority for improving fuel efficiency of automotive [1, 2]. 7xxx-series aluminum alloys (AlZnMgCu) offer a potential to replace a portion of high strength steels [3,4,5]; formability of AA7xxx at ambient temperatures is limited
The formability of aluminum alloys under warm conditions can be evaluated by forming limit curves (FLCs) [10, 11]
EN AW-7075-T6 using the Nakazima tests and found that the major strain of FLC raised from 0.15 to 0.3 at plane strain condition as the temperature increased from room temperature to 230 °C

Summary

Introduction

Lightweight materials, e.g., advanced high strength steels and aluminum alloys, have been identified as a key priority for improving fuel efficiency of automotive [1, 2]. 7xxx-series aluminum alloys (AlZnMgCu) offer a potential to replace a portion of high strength steels [3,4,5]; formability of AA7xxx at ambient temperatures is limited. The accuracy of numerical simulation is dependent on the constitutive model which describes the plastic deformation behavior of sheet metals. Studies have been carried out on the influence of constitutive models on the prediction accuracy of finite element analysis (FEA) for the sheet metal forming processes. There are some investigations on the yield behavior of sheet metals at elevated temperatures. Sheet metals are usually subjected to multiple deformation paths during forming processes, and the multiaxial formability of sheets cannot be merely investigated through the uniaxial tests. There are few works focused on the yield behavior of AA7075-T6 under biaxial loading condition at warm temperatures, and the applicability of various constitutive models requires further investigation. The influence of the exponent in the Yld2000-2d criterion on yield loci was investigated to improve the prediction accuracy

Experimental Details

Results and Discussion

Conclusions