| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系 === 102 === Strain-induced melt activation (SIMA) is a process with development potential due to its simplicity and low cost. The semisolid billet of AZ61 Mg alloy was fabricated by the hot extruded SIMA process. The effects of extrusion ratio and heating condition on the microstructure feature, the semi-solid forming mechanism and compressive properties were discussed. The grain became more globular with appropriately increasing the reheating temperature and holding time. The dominant mechanism of grain coarsening at initial stage was grain coalescence, while Ostwald ripening at longer holding time. The deformation resistance of Mg alloys after SIMA process was lower than as-extruded at 500℃, 520℃, and 540℃. SIMA Mg alloys had the advantage of near net shape. To evaluate ductility of SIMA and as-extruded Mg alloys was by bending test. The ductility of SIMA Mg alloys was improved after heating treatment.
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