Identification of the threshold stress and true activation energy for characterizing the deformation mechanisms during hot working. (5th January 2017)

• Record Type: Journal Article
• Authors: Wang, S.; Luo, J.R.; Hou, L.G.; Zhang, J.S.; Zhuang, L.Z.
• Is Part Of: Materials & design. Volume 113(2017)
• Page Start: 27
• Page End: 36
• Publication Date: 2017-01-05
• Subjects: True activation energy -- Aluminum alloy -- Constitutive model -- Creep -- Threshold stress; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2016.10.018
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: For characterizing the origins of threshold stress and the evolution of deformation mechanisms in hot working region, the hyperbolic-sine constitutive analyses were conducted to determine the threshold stress σ 0, the true stress exponent n t and the true activation energy Q t in AA7050 Al alloys. The origins of σ 0 could be related to the four bypassing mechanisms of dislocations overcoming an obstacle. The origins of σ 0 are the local climb at 603–633 K, and it may change from the local climb to the detach stress with increasing strains at 663–693 K. The n t and Q t after Young's modulus and threshold stress correction can be associated with the specific deformation mechanism. The deformation mechanisms at peak strains may change from the climb-controlled dislocation creep (lattice diffusion) at 603 K to the Zn diffusion controlled solute drag creep which is controlled by (sub)grain boundary diffusion at 693 K. The n t and Q t decrease with increasing strains may be attributed to the grain boundary self-diffusion accelerated by the fluxes of vacancies for lower temperatures (603–663 K) and the atom diffusion controlled solute drag creep accelerated by the vacancies, (sub)grain boundaries, and the motion of high angle grain boundaries for higher temperatures (663–693 K), respectively. Graphical abstract: Highlights: The hyperbolic-sine constitutive analyses were conducted to determine the true stress exponent and activation energy in hot working region. The origins of threshold stress could be related to the bypassing mechanism of dislocations over a particle. The evolution of deformation mechanisms during hot working could be reflected by the true stress exponent and activation energy. The effects of temperature and strain on the true stress exponent and activation energy were discussed.