銅、鎂含量與熱處理對Al-14.5Si-Cu-Mg合金拉伸、熱穩定與磨耗性質之影響; Effects of Cu, Mg contents and heat treatment on tensile, thermal stability and wear properties of Al-14.5Si-Cu-Mg alloys

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Title:	銅、鎂含量與熱處理對Al-14.5Si-Cu-Mg合金拉伸、熱穩定與磨耗性質之影響;Effects of Cu, Mg contents and heat treatment on tensile, thermal stability and wear properties of Al-14.5Si-Cu-Mg alloys
Authors:	吳志庭;Chih-Ting Wu
Contributors:	機械工程研究所
Keywords:	磨耗;富鐵相;拉伸性質;過共晶;熱處理;銅鎂含量;熱穩定性;Cu and Mg contents;Tensile properties;Thermal stability;Wear;Iron-bearing phase;Heat treatment;Hypereutectic
Date:	2011-08-22
Issue Date:	2012-01-05 12:33:57 (UTC+8)
Abstract:	本研究配製三種不同銅、鎂含量之Al-14.5Si-Cu-Mg合金，探討銅、鎂含量與熱處理對Al-14.5Si-Cu-Mg合金拉伸、熱穩定和磨耗性質的影響。結果顯示低銅鎂比合金中含有文字形Al8Mg3FeSi6富鐵相;高銅鎂比合金則含有針狀β-Al5FeSi富鐵相，經T6熱處理後，前者之拉伸強度與伸長率皆較後者為佳，高銅鎂比合金中的針狀β-Al5FeSi6富鐵相和伴隨針狀β-Al5FeSi6富鐵相產生之縮孔皆是導致拉伸強度與伸長率下降之原因。高銅高鎂合金因含較多質硬的Al2Cu與Al5Cu2Mg8Si6相，在鑄態合金中硬度最高，但經T6熱處理後，該合金硬度卻不如高銅低鎂合金，增加鎂含量雖可析出更多λ’(Al5Cu2Mg8Si6)強化相，但卻也減少了θ’(Al2Cu)強化相的析出，導致λ’和θ’總析出量降低，影響析出硬化的效果。經300℃x100h等溫熱處理後，λ’和θ’析出強化相轉變成λ和θ平衡相，導致T6熱處理合金硬度大幅降低，熱穩定性遠不如鑄態合金。此外，不論鑄態或T6熱處理合金經等溫熱處理後，高銅含量有較佳之硬度表現，高鎂含量則無顯著影響。試片經等溫熱處理後進行磨耗試驗，在10N的荷重下，主要磨耗型式是研磨磨耗;在40N的荷重下，則呈現粘著磨耗，磨耗率隨著荷重增加而顯著上升，T6熱處理低銅低鎂合金磨耗率最高，而鑄態高銅高鎂合金之磨耗率最低，磨耗率隨著硬度增加而減少。增加銅含量可降低磨耗率，鑄態合金之抗磨耗性較T6熱處理合金為佳。 Three Al-14.5Si-Cu-Mg alloys with different copper and magnesium contents were prepared to investigate the effects of copper, magnesium contents and heat treatment on tensile, thermal stability and wear properties of Al-14.5Si-Cu-Mg alloys. The results indicated that the low copper to magnesium ratio alloy contained Al8Mg3FeSi6 and high copper to magnesium ratio alloy contained the acicular β-Al5FeSi. The tensile strength and elongation of the low copper to magnesium ratio alloy is superior to those of the high copper to magnesium ratio alloy. The presence of the acicular β-Al5FeSi and shrinkage porosity caused by acicular β-Al5FeSi in the high copper to magnesium ratio alloy were responsible for the reduction in tensile strength and elongation. Due to its large amount of the hard Al2Cu and Al5Cu2Mg8Si6, the alloy with high copper and high magnesium contents had the highest hardness in as-cast condition. After T6 heat treatment, the hardness of the alloy which contained high copper and low magnesium contents was superior to that of the alloy which contained high copper and low magnesium contents. Adding more magnesium could increase the precipitation of λ’(Al5Cu2Mg8Si6) but it also lowered that of θ’(Al2Cu), decreasing the total precipitation of λ’ and θ’. The λ’ and θ’ strengthening precipitates converted to stable λ and θ phases led to a severe decrease in hardness following isothermal heat treatment at 300℃ for 100h. The thermal stability of the T6 heat-treated alloys was much worse than that of the as-cast alloys. In addition, increasing copper content could enhance the hardness of as-cast and T6 heat treated alloys after isothermal heat treatment. This result could not be obtained by increasing magnesium content. The specimens were isothermally heat-treated prior to wear test. The type of wear was abrasive wear under 10N applied load and adhesive wear was observed under 40N applied load. The wear rate markedly increased with increasing applied load. The T6 heat-treated alloy with low copper and low magnesium contents had highest wear rate; the as-cast alloy with high copper and high magnesium contents had the lowest wear rate. The wear rate decreased with the increase in the hardness. Increasing copper content could lower wear rate. The wear resistance of the as-cast alloys was better than that of the T6 heat-treated alloys.
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