Si對Al-64vol%SiC複合材料機械與熱性質之影響;Effect of Si on the mechanical and thermal properties of Al-64vol%SiC composite

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题名:	Si對Al-64vol%SiC複合材料機械與熱性質之影響;Effect of Si on the mechanical and thermal properties of Al-64vol%SiC composite
作者:	高廷鈞;Kao, Ting-Jun
贡献者:	材料科學與工程研究所
关键词:	鋁矽合金;鋁-碳化矽複合材料;體積分率;顆粒尺寸;硬度;抗彎強度;導熱係數;熱膨脹係數
日期:	2025-08-06
上传时间:	2025-10-17 11:49:29 (UTC+8)
出版者:	國立中央大學
摘要:	本研究採用低壓滲透法，並於常溫環境條件下，分別以三種Si含量（0、7、12 wt%）之鋁合金為基材，製備SiC體積分率為50%與64%，且顆粒尺寸分別為120μm與40μm之Al-SiC複合材料，藉此探討Al基Si含量對不同SiC體積分率與顆粒尺寸之複合材料密度、微結構、硬度、抗彎強度、導熱係數與熱膨脹係數之影響。研究結果顯示，Si元素可降低Al合金熔點，提升其流動性，使液態鋁更容易滲透至SiC顆粒間隙，從而提高材料之緻密性與整體密度。此外，Al-50 vol% SiC複合材料由於體積分率較低且顆粒尺寸較大，使其顆粒間距相對增加，有助於液態鋁充分滲入，導致其緻密度高於Al-64 vol% SiC複合材料。而由於Si與SiC皆具高硬度，且SiC顆粒尺寸縮小可增加其與基材之界面面積，進一步強化複合材料的硬化效果。抗彎強度則因材料緻密性提升而初步上升；然而，隨Si含量提高，共晶Si比例上升，而該相為硬脆相，於抗彎測試下易破斷並成為裂紋起始點，導致抗彎強度呈現先升後降之趨勢。另一方面，SiC體積分率提高與顆粒尺寸縮小可有效阻擋裂紋擴展，故Al-64 vol% SiC複合材料之抗彎強度普遍高於Al-50 vol%者。此外，片狀共晶Si會干擾電子與聲子之傳遞路徑，使比熱隨Si含量上升而下降，且SiC體積分率提高與顆粒尺寸縮小皆會增大界面面積，進一步提高電子與聲子散射機率，使Al-64 vol% SiC複合材料之比熱普遍較低。另一方面，因複合材料緻密度隨Si含量上升而提升，使電子與聲子散射機率降低，進而使熱擴散係數上升。然而，在Al-7Si與Al-12Si製備之Al-50 vol% SiC複合材料中，由於兩者孔隙率相近，但由於 Al-12Si基地內部共晶Si比例較高，使得其所製複材之熱擴散係數反而下降。最後，由於Si與SiC的熱膨脹係數較Al低，因此其含量增加可使材料受熱時有效抑制基材膨脹，致使整體熱膨脹係數降低。此外，顆粒尺寸縮小使基材與SiC界面面積增加，也進一步提升抑制基材的膨脹，進一步降低複合材料的熱膨脹係數。 ;Using a low-pressure infiltration method at room temperature, aluminum alloys with three different silicon contents (0, 7, and 12 wt%) were used to fabricate Al-SiC composites with SiC volume fractions of 50% and 64% and particle sizes of 120 μm and 40 μm, Then discuss the effects of silicon content on the density, microstructure, hardness, flexural strength, thermal conductivity, and thermal expansion behavior of the composites were systematically investigated. The results show that the addition of silicon lowers the melting point of the aluminum alloy, thereby enhancing the fluidity of the molten aluminum. This facilitates infiltration into the interstitial spaces between SiC particles, improving the densification and overall density of the composites. Furthermore, due to the lower volume fraction and larger particle size, the Al–50 vol% SiC composites exhibited wider particle spacing, which facilitated the full infiltration of the aluminum melt and resulted in a higher density compared to the Al–64 vol% SiC composites. Both Si and SiC possess high hardness, and the reduction in SiC particle size increases the interfacial area with the matrix, thereby enhancing the hardening effect of the composites. Bending strength initially increased with improved densification; however, increasing Si content also led to a higher proportion of eutectic Si. As a hard and brittle phase, eutectic Si is prone to fracture and tends to act as a crack initiation site under bending loads, resulting in a trend where bending strength first increases and then decreases. On the other hand, a higher SiC volume fraction and smaller particle size effectively hindered crack propagation, resulting in Al–64 vol% SiC composites generally exhibiting higher bending strength than their 50 vol% counterparts. In addition, the lamellar eutectic Si phase disrupted the pathways of electron and phonon transport, causing specific heat capacity to decrease with increasing Si content. A higher SiC volume fraction and smaller particle size also enlarged the interfacial area, raising the scattering probability of electrons and phonons, which made the specific heat of Al–64 vol% SiC composites generally lower. However, since densification improved with higher Si content, the scattering of electrons and phonons was reduced, thereby increasing thermal diffusivity. Finally, due to the significantly lower coefficients of thermal expansion of Si and SiC compared to Al, increasing their content effectively restrained the thermal expansion of the Al matrix, resulting in a lower overall CTE. Additionally, the smaller SiC particle size increased the interfacial area between the matrix and the reinforcement, further limiting the expansion of the matrix and reducing the CTE of the composite.
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