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Texture control of AZ31 Mg alloy using {10-12} twin and enhanced stability of twin-structure

Title
Texture control of AZ31 Mg alloy using {10-12} twin and enhanced stability of twin-structure
Authors
이정훈
Date Issued
2015
Publisher
포항공과대학교
Abstract
The present dissertation aims at controlling texture using deformation {1 0 -1 2} twins and enhancing the effect of texture control to improve the mechanical properties of AZ31 magnesium alloy. First, the importance of initial {10-12} twins in the formation of deformation texture was investigated by conducting strain path change tests of rolled Mg-3Al-1Zn alloy in which {10-12} twinning dominated the deformation. The existence of initial twins changed a twinning process by preferring the growth of initial twins rather than the nucleation of new twins, which led to a non-Schmid behavior of twinning characteristics and consequently caused a completely different deformation texture compared with the counterpart without initial twins. Second, the effect of texture control using {1 0 -1 2} twins was capable of being significantly improved by thermal annealing. The removal of the residual tensile stress that developed inside these twins along the c-axis retarded detwinning activity during early deformation by increasing the detwinning stress, and this consequently led to a prolonged and enhanced activity of basal slip in the twinned region, increasing its contribution to the deformation. On the basis of this mechanism, the yield strength and elongation were improved simultaneously. Finally, a remarkable improvement in the tensile yield strength of rolled Mg-3Al-1Zn alloy with pre-existing {10-12} twins was achieved by compression causing double twinning. The formation of {10-12}-{10-12} double twins inside pre-existing {10-12} twin bands by compressive deformation effectively suppressed the detwinning of the pre-existing twins during subsequent deformation, and thereby maintained the effect of texture control using {1 0 -1 2} twins. This in turn led to a change in the dominant deformation mode from detwinning to slip, significantly increasing the yield strength. The mechanisms of this induced non-detwinning behavior are discussed.
URI
http://postech.dcollection.net/jsp/common/DcLoOrgPer.jsp?sItemId=000001914088
https://oasis.postech.ac.kr/handle/2014.oak/93016
Article Type
Thesis
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