Mechanism and Modelling Studies of Elastic-plastic Stress Relaxation of Aluminium Alloys Based on Thermally Activated Plastic Theories

doi:10.3901/JME.2022.06.042

Abstract

Abstract: Aiming at the inconsistent of mechanisms and insufficient prediction models for stress relaxation of aluiminium alloys in elastic and plastic regions, a method that utilises thermally activated plastic deformation theories for mechanism characterisation and modelling during stress relaxation ageing (SRA) process in both elastic and plastic regions is proposed. The apparent activation volumes obtained from the theories for AA7B04 and AA6082 alloys indicate a dislocation-obstacles interaction mechanism for stress relation in both elastic and plastic regions. The stress relaxation behaviour in elastic region is found to be mainly affected by the effective stress, while the more significant stress relaxation in plastic region has been attributed to the combined effect of increasing effective stresses and decreasing apparent activation energies, which have been quantified by the theories in this study. Based on these theoretical analysis results, a simple constitutive model considering the changing apparent energies has been proposed, providing an effective way to successfully predict the different stress relaxation behaviour of aluminium alloys under various stress levels in the elastic-plastic deformation range for potential CAF process applications. The proposed method overcomes limitations of the conventional creep stress exponent analysis method for SRA behaviour analysis, and provides abundant information (i.e. stress components, apparent activation volumes and energies) to support the characterization of deformation mechanisms in SRA and enable accurate prediction of different SRA behaviour in elastic and plastic regions.

Key words: aluminium alloys, stress relaxation, internal stress, effective stress, activation energy, constitutive modelling

CLC Number:

TG156

LI Yong, SHI Zhusheng, Lü Fenggong, RONG Qi, LI Dongsheng, LIN Jianguo. Mechanism and Modelling Studies of Elastic-plastic Stress Relaxation of Aluminium Alloys Based on Thermally Activated Plastic Theories[J]. Journal of Mechanical Engineering, 2022, 58(6): 42-51.

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