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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。
The non-equilibrium solidified test bars of AZ91 + 0.75% Er (mass fraction) rare earth magnesium alloy were prepared by copper die casting. The effects of low temperature aging and high temperature solid solution on the microstructure and microhardness of the alloy were studied. The results show that the addition of rare earth elements and cooling rate are conducive to the refinement of AZ91 magnesium alloy, of which the latter effect is more obvious. The solute retention effect under quenching conditions can also eliminate the Al-Er acicular phase in the as-cast rare-earth magnesium alloy. Unbalanced solidified alloy after 200 ℃ aging treatment, β-phase precipitation from supersaturated solid solution. After aging for 16 h, the Mg-Er rare earth compound phase formed from the matrix in the form of particle agglomeration. When the solid solution treatment at 420 ℃, the β phase dissolves in the non-equilibrium solidified alloy, and the grain morphology changes into the polygonal equiaxed grain structure. The average grain size increases with the increase of solution time. Unbalanced solidification and subsequent aging treatment can effectively improve the microhardness of the rare earth magnesium alloy, while the alloy solution hardness decreased.