本研究在探討含Cu之Al-12.5Si-1.0Mg合金之高溫（300℃）熱穩定性與耐磨性。結果顯示，低Cu（2.55wt.%）合金之鑄態微結構包括鋁矽共晶相、Al2Cu相(θ)、Al5Cu2Mg8Si6相(λ)及Mg2Si相(β)，而高Cu（4.53wt.%）合金之鑄態微結構除了未觀察到Mg2Si相(β)外，其餘組成與低Cu合金相似。合金經固溶處理後，高Cu合金鋁基地中的Cu原子固溶量比低Cu合金高，時效處理後，析出大量Al2Cu相(θ)、Al5Cu2Mg8Si6相(λ)，提升合金之硬度。高Cu合金於鑄態時，鋁基地中晶出大量Al2Cu相與Al5Cu2Mg8Si6相，而此晶出相經300℃×10hr處理後仍然存在於鋁基地中，致使合金硬度下降幅度減少（約HRF89→HRF75），熱穩定性良好。而時效處理後之合金雖有析出相提升合金硬度，但析出相經300℃×10hr後會產生明顯過時效現象，致使合金硬度大幅下降（約HRF104→HRF57），熱穩定性不如鑄態合金。在低荷重（10N）進行磨耗時，含高低Cu之鑄態與時效處理後之合金，經300℃×100hr處理後之磨耗量相似；但在高荷重（40N）時，合金耐磨性之趨勢與硬度相符，鑄態高Cu合金經300℃×100hr處理後硬度最高，具有最佳耐磨性。

Effect of Cu content on microstructure and mechanical properties of Al-12.5Si-1.0Mg alloys were investigated by adding two kinds of Cu contents (2.55wt.%, 4.53wt.%) into the alloys. The results indicate that microstructural constituents of low-Cu alloys consist of eutectic Al-Si, Al2Cu, Al5Cu2Mg8Si6 and Mg2Si coexist at the Al-matrix. Increasing the Cu content will reduce Mg2Si but increase Al2Cu and Al5Cu2Mg8Si6. Effect of soluting atoms and precipitation hardening increases with the increasing of Cu content, this leads to higher hardness in high-Cu alloys. But the precipitation phase change from coherence or semi-coherence to non- coherence, and the hardness of alloys will decline. The foundry high-Cu alloys after 300℃×100hr treatment contains much intermetallic compounds and shows the best thermal stability. After wear test with 10N load, each alloy shows the same wear rate. When load is 40N, the foundry high-Cu alloy after 300℃×100hr treatment shows the lowest wear rate.

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