Stress Relaxation Aging Behavior and Constitutive Modelling of AA7150-T7751 under Different Temperatures, Initial Stress Levels and Pre-Strains

Yixian Cai,Jianguang Wang,Lan Hu,Qing Wang,Xing Zhao,Gengquan Jin,Minghui Huang,Canyu Tong,Lihua Zhan,Lingzhi Xu,Chunhui Liu,Yongqian Xu

doi:10.3390/met9111215

Yixian Cai, Jianguang Wang + Show 10 more

Open Access

https://doi.org/10.3390/met9111215

Copy DOI

Abstract

Age forming is an advanced manufacture technology for forming large aluminum panels. Temperature, initial stress level and pre-strains have a great effect on the formability and performance. The stress relaxation aging behavior of AA7150-T7751 under different temperatures, initial stress levels and pre-strains was studied through stress relaxation tests, tensile tests and TEM observations. The results show that the formability can be improved with the increase of temperature, initial stress levels and pre-strains. Deformation mechanisms during stress relaxation of the material were analyzed on the basis of creep stress exponent and apparent activation energy. The aging precipitates of the studied alloy were not sensitive to the age forming conditions, but drastically coarsened at over aging temperature, which decreased the mechanical properties. In addition, the relationship between stress relaxation behavior and aging strengthening is discussed. Based on the dislocation theory and the modified Arrhenius equation, a stress relaxation constitutive equation considering the initial mobile dislocation density and temperature dependent activation energy was established. This model can predict very well the stress relaxation behavior under various temperature, stress level and pre-strain conditions, with an average error of 2%.

Highlights

Age forming (AF) technology was conceived in the 1970s by Textron Aerostructures to produce components with high strength and complex curvatures in the aeronautical industry [1]
In this paper, based on the Asinh(Bσ) model and the hardening and recovery theories, we proposed a stress relaxation model with considering the pre-strains, initial stress and temperature
When the temperature rises by 30 ◦ C, the initial stress level increases by 100 MPa and pre-strain value increases by 3%, relaxing efficiency increased by 16.48%, 7.96% and 17.72%, respectively, compared with SRA at 300 MPa under 140 ◦ C for 16 h

Summary

Introduction

Age forming (AF) technology was conceived in the 1970s by Textron Aerostructures to produce components with high strength and complex curvatures in the aeronautical industry [1]. Zhan et al [4] and Zheng [5] outlined several important process parameters that affect the quality and precision of age forming, including aging time, aging temperature and initial stress level. Metals 2019, 9, 1215 simulation regarding the deformation behavior and mechanical property evolution of materials in age forming relies on the establishment of a unified constitutive equation on the basic of deformation and strengthening mechanism. In order to realize the precise manufacturing of components, it is necessary to understand the comprehensive influence of process parameters and initial states on age forming so as to come up with an accurate prediction model

Results

Discussion

Conclusion