Cu含量對鑄造Mg-3Zn-xCu-0.6Zr鎂合金時效析出行為的影響Effects of Cu addition on aging precipitation behavior of cast Mg-3Zn-xCu-0.6Zr magnesium alloys

研究銅含量對鑄造Mg-3Zn-xCu-0.6Zr 鎂合金時效行為的影響，利用金相顯微鏡、掃描電鏡、透射電鏡、顯微硬度計和X 射線衍射儀確定T6 時效處理后Mg-3Zn-xCu-0.6Zr 鎂合金中主要析出相的形態、數量和種類。結果表明：含Cu 的Mg-3Zn-0.6Zr 合金經180 ℃時效后，主要析出強化相是以其軸線垂直于基面(0001)Mg 的板條狀β 2′ -MgZn2，其次是以其軸線平行于基面(0001)Mg的短棒狀β-MgZn；晶界共晶組Mg+(Mg2Cu，CuMgZn)基本保持不變；Cu 含量越大(w(Cu)＜2.0%)，析出相的數量越多、分布越彌散，平均晶粒尺寸越小；Cu 的加入一方面提高合金的固溶溫度，提高固溶處理后合金中的空位濃度，因而顯著促進析出相的空位形核和析出密度；另一方面，Cu 的加入還能有效促進 Zn 在鎂基體中的擴散，隨 Cu 含量的增加，β 2′ -MgZn2數量隨之增多，Zn 的消耗隨之增加，β-MgZn 相卻減少。

The effects of Cu addition on the aging behavior of cast Mg-3Zn-xCu-0.6Zr alloys were investigated. The morphology, number and type of the precipitates formed in T6 aging Mg-3Zn-xCu-0.6Zr alloys were determined by optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy(TEM), Vickers-hardness and X-ray diffractometry (XRD). The results show that the primary strengthening precipitate formed in the Cu-containing Mg-3Zn-0.6Zr alloys aged at 180 ℃ is the lath-shaped β 2′ -MgZn2 with its axis perpendicular to the base plane (0001)Mg, and the second one is the shot-rod shaped β-MgZn with its axis parallel to the base plane (0001)Mg. The grain boundary eutectic Mg+(Mg2Cu, CuMgZn) does change during the aging course. With increasing Cu content to 2% (mass fraction), the precipitates increase and distribute dispersively, and the average sizes decrease. The addition of Cu can enhance the solution temperature for the alloys, thus increasing the density of the vacancy which is supposed to play a crucial role in the precipitate nucleation and hence in increasing the precipitation density. In addition, Cu can promote the diffusivity of Zn in the Mg matrix, therefore facilitating the nucleation and growth of the precipitates. With increasing Cu content the amount of β 2′ -MgZn2 increases, on the other hand, the amount of β-MgZn decreases with the increasing consumption of Zn.

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