非平衡凝固AZ91+0.75%Er镁合金及其热处理

Non-equilibrium Solidification of AZ91+0.75%Er Magnesium Alloy and Subsequent Heat Treatment

采用铜模喷铸技术制备出AZ91+0.75%Er(质量分数)稀土镁合金非平衡凝固试棒,研究了低温时效及高温固溶对合金组织和显微硬度的影响规律。结果表明,稀土元素的添加及冷却速率的提高均有利于细化AZ91镁合金组织,其中后者影响效果更加明显。急冷条件下的溶质截留效应还可以消除铸态稀土镁合金中的Al-Er针状化合物相。非平衡凝固合金经200℃时效处理后,β相从过饱和固溶体中析出。时效16 h后,Mg-Er稀土化合物相以颗粒团聚状从基体中形成。420℃固溶处理时,非平衡凝固合金中β相发生溶解,晶粒形貌转变为多边形等轴晶组织,平均晶粒尺寸随固溶时间的延长而不断增加。非平衡凝固及后续时效处理可有效提高稀土镁合金的显微硬度,而固溶条件下合金硬度值有所降低。

Non-equilibrium solidification samples of AZ91＋0.75wt%Er magnesium alloy were fabricated by a copper mould spray-casting technique. The effects of aging and solid solution treatments on microstructure and micro-hardness were researched. It is shown that both the addition of rare earth element and increase of cooling rate are advantageous to the refinement of AZ91 alloy, among which the latter plays a more important role. Moreover, the solute trapping from rapid quenching eliminates the occurrence of acicular A1-Er compound. After aging at 200 ℃, β phase precipitates from the super-saturated solid solution. With increasing isothermal time to 16 h, Mg-Er phase is generated with cluster distribution. As for solution temperature of 420 ℃, the grain appears distinctly because of the dissolution of eutectic phase, and the average size of primary grain increases with extending solution time. The hardnesses of non-equilibrium solidified and aged AZ91＋0.75%Er alloy are enhanced continuously in comparison to that of as-cast ingot. However, a weak reduction of hardness occurs after solution treatment.