本研究使用AZ91合金作為基材，使用粒徑尺寸50 nm與1 μm SiC顆粒，固定添加碳化矽比例2 wt.%分別製成單一粒徑尺寸(50 nm、1 μm)複合材料與同時添加不同粒徑尺寸(50 nm+1 μm)複合材料，以攪拌鑄造的方式製成鎂基複合材料，並對成分、顯微結構、機械性質進行分析，探討同時添加不同粒徑碳化矽之比例對AZ91合金影響。
研究結果顯示，SiC顆粒製成之鎂基複材，其相組成均為α-Mg、Mg17Al12、Al-Mn相及SiC。透過顯微結構觀察發現，添加SiC具有晶粒細化及提高共晶相生成的作用，複合材料的晶粒尺度由420 μm下降至94 μm，共晶比例由23%提升至40%。此外1 μm粒徑尺寸碳化矽顆粒有相互團聚的現象，當添加量超過1 wt.%時碳化矽顆粒會於晶界處大量團聚形成孔洞，造成複合材料抗拉強度與延性下降。本研究最佳之不同粒徑SiC添加比例為同時添加1 wt.% 1 μm與1 wt.% 50 nm，SiC在材料內均勻分布，材料內部無孔洞，與AZ91合金相比其降伏強度由57 MPa增加至115 MPa， 抗拉強度由86 MPa增加至195 MPa，伸長率由1.1%增加至4.7%。

In this study, AZ91 alloy was used as the matrix, and SiC particles with different amount and particle size were used as reinforcement. The magnesium-based composite material was prepared by stirring casting. SiC particles with particle size of 50 nm and 1 μm, and a fixed amount of 2 wt%, was used to make a single particle size (50 nm, 1 μm) composite and with bimodal particle size (50 nm+ 1 μm) composite materials. Analysis of composition, microstructure, and mechanical properties was performed to study the effect of bimodal size of SiC on the AZ91 alloy.
The results show that the phase content of magnesium-based composites was α-Mg, Mg17Al12, Al-Mn particles and SiC. Through the microstructure observation, it was found that the addition of SiC resulted in grain refinement and increase of eutectic phase. The grain size of the composite decreased from 420 μm to 94 μm, and the eutectic ratio increased from 23% to 40%. In addition, the 1 μm particle size SiC particles have agglomeration. When the amount of SiC exceeds 1 wt.%, the SiC particles will agglomerate at a large amount at the grain boundary to form pores, resulting in a decrease in tensile strength and ductility of the composite. In this study, the optimum ratio of SiC added with different particle sizes is 1 wt.% 1 μm and 1 wt.% 50 nm. SiC is evenly distributed in the composite material. There is no pore inside the material. Compared with AZ91 alloy, the yield strength increased from 57. MPa to 115 MPa, the ultimate strength increased from 86 MPa to 195 MPa, and the elongation increased from 1.1% to 4.7%.

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