Cu含量对铸造Mg-3Zn-xCu-0.6Zr镁合金时效析出行为的影响Effects of Cu addition on aging precipitation behavior of cast Mg-3Zn-xCu-0.6Zr magnesium alloys

研究铜含量对铸造Mg-3Zn-xCu-0.6Zr 镁合金时效行为的影响，利用金相显微镜、扫描电镜、透射电镜、显微硬度计和X 射线衍射仪确定T6 时效处理后Mg-3Zn-xCu-0.6Zr 镁合金中主要析出相的形态、数量和种类。结果表明：含Cu 的Mg-3Zn-0.6Zr 合金经180 ℃时效后，主要析出强化相是以其轴线垂直于基面(0001)Mg 的板条状β 2′ -MgZn2，其次是以其轴线平行于基面(0001)Mg的短棒状β-MgZn；晶界共晶组Mg+(Mg2Cu，CuMgZn)基本保持不变；Cu 含量越大(w(Cu)＜2.0%)，析出相的数量越多、分布越弥散，平均晶粒尺寸越小；Cu 的加入一方面提高合金的固溶温度，提高固溶处理后合金中的空位浓度，因而显著促进析出相的空位形核和析出密度；另一方面，Cu 的加入还能有效促进 Zn 在镁基体中的扩散，随 Cu 含量的增加，β 2′ -MgZn2数量随之增多，Zn 的消耗随之增加，β-MgZn 相却减少。

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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