Characterisation of precipitate phases in magnesium alloys using electron microdiffraction |
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Authors: | J. F. Nie X. L. Xiao C. P. Luo B. C. Muddle |
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Affiliation: | a Department of Materials Engineering, Monash University, Clayton, Victoria 3800, Australia b Department of Mechano-Electronic Engineering, South China University of Technology, Guangzhou, China |
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Abstract: | Recent results of the characterisation of the structure, morphology and orientation of fine-scale, strengthening precipitate phases in selected magnesium alloys using transmission electron microscopy and microdiffraction are reviewed. The strengthening precipitate phases in Mg–Y–Nd alloys, aged to maximum hardness at 250°C, have been found to include two metastable precipitate phases β′ and β1, and the equilibrium precipitate β. The β′ phase has a globular form, a base-centred orthorhombic structure (potential point group of mmm), and an orientation relationship such that (100)β′//(110)α, [001]β′//[0001]α. The β1 phase has an f.c.c. structure (space group and an orientation relationship that may be described by (100)β1//[0001]α, and forms as plates parallel to The β phase has an f.c.c. structure (space group ) and also forms as plates on with an orientation relationship with the matrix phase that is identical to that observed for β1 phase. Precipitates in Mg–Al alloys, aged isothermally at 200°C, invariably have the b.c.c. structure of the equilibrium precipitate phase β (Mg17Al12). Three orientation relationships have been observed between β and the matrix phase. Most precipitates have an irrational orientation relationship that approximates to the Burger's relationship, (001)β//(0001)α, and a faceted lath morphology with habit plane parallel to (0001)α. A minor fraction of precipitates posses an orientation relationship that is of the form Full-size image and have a prismatic rod morphology. The long axes of these rods are parallel to [0001]α, and their faceted surfaces are parallel to A few precipitates are observed to have an orientation relationship such that Full-size image and a rod shape, with their long axes apparently inclined with respect to [0001]α. |
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Keywords: | Magnesium alloys Crystal structure Precipitate morphology Orientation relationships Transmission electron microscopy Electron microdiffraction Microstructure |
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