Development of novel grain morphology during hot extrusion of magnesium AZ21 alloy |
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Authors: | MA Azeem A Tewari S Mishra S Gollapudi U Ramamurty |
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Affiliation: | 1. Department of Materials Engineering, Indian Institute of Science, Bangalore 560 012, India;2. GM Technical Centre India Pvt. Ltd., Whitefield Road, Bangalore 560 066, India |
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Abstract: | Microstructure and microtexture evolution during static annealing of a hot-extruded AZ21 magnesium alloy was studied. Apart from fine recrystallized equiaxed grains and large elongated deformed grains, a new third kind of abnormal grains that are stacked one after the other in a row parallel to the extrusion direction were observed. The crystallographic misorientation inside these grains was similar to that of the fine recrystallized grains. The large elongated grains exhibited significant in-grain misorientation. A self-consistent mechanistic model was developed to describe the formation of these grain morphologies during dynamic recrystallization (DRX). The texture of pre-extruded material, although lost in DRX, leaves a unique signature which manifests itself in the form of these grain morphologies. The origin of abnormal stacked grains was associated with slow nucleation in pre-extruded grains of a certain orientation. Further annealing resulted in large secondary recrystallized grains with occasional extension twins. |
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