A new unequal channel angular pressing (UCAP) procedure is proposed for ultrafine-grained metals and alloys. The microstructures and mechanical properties of Mg-5.8Zn-1.2Y-0.7Zr alloys subjected to unequal channel angular pressing (UCAP) are investigated. It is found that the optimum condition in UCAPed alloy is obtained at 523 K with a largest elongation to failure of 13.1% and ultimate tensile strength of ~400 MPa. Microstructural observations show that the grain size is refined to ~1.0 μm during UCAP. The probable mechanisms for these high mechanical properties are attributed to grain size and destroyed secondary phase strengthening effects and fine precipitates formed during pressing at high temperature by severe shear and plastic deformation.
Mg-5.8Zn-1.2Y-0.7Zr alloy consists of α-Mg, Mg3Zn6Y and Mg3Zn3Y2 phases in the unpressed condition. The microstructure of the cast alloy in the homogenized state was coarse-grained with an average grain size of about 110 µm, processing by UCAP produced considerable grain refinement. Mg3Zn6Y phases were destroyed into small particles. These particles played a strengthening role in the UACPed alloy and led to a final ultimate tensile strength of ~400 MPa and sufficient ductility of ~ 13.1%.
5. Acknowledgements
The study was financially supported by both the Key Science and Technology Program of Shanxi Province, China (No. 20090322007), and the project of innovation of Shanxi Province Postgraduates (No. 20100392).
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