【摘要】 研究了添加混合稀土（0．02%—1．2%,质量分数）对AZ91D镁合金晶粒大小、枝晶大小、共晶组织,凝固曲线特征参数和力学性能的影响．结果表明,混合稀土与合金中Al₈（Fe,Mn）₅或ε-AlMn相反应生成Al-RE-Mn三元相,减少了合金熔体中异质形核核心的数目,从而导致晶粒和枝晶的粗化；混合稀土还与Al反应生成Al₁₁RE₃相,消耗了部分Al,使得共晶组织减少．在砂型凝固条件下,随着混合稀土添加量的增加,AZ91D镁合金的初晶形核最低温度从595．2升到597．3℃；共晶最低温度先从427．7升到431．2℃,再降到428．7℃；共晶生长温度先从428．7升到431．8℃,再降到429．9℃；共晶再辉温差则存在波动．添加混合稀土降低了AZ91D镁合金的室温强度,但提高了合金的高温强度和延伸率．更多还原

【Abstract】 The effects of mischmetal addition ranging from 0.02% to 1.2% on the grain size, dendrite size,eutectic microstructure,characteristic parameters in the cooling curve and mechanical properties of AZ91D magnesium alloy were investigated.The results showed that mischmetal reacted with Als（Fe,Mn）₅ orε-AlMn phases as the heterogeneous nuclei in the melt,and formed Al-RE- Mn phases,thus the amount of the heterogeneous nuclei reduced,resulting in the grain and dendrite coarsening.In addition,mischmetal reacted with aluminum to form Al₁₁RE₃ phases,which consumed a portion of aluminum atoms,and reduced the amount of the eutectic microstructure.Under the condition of the sand mold,the lowest temperature of primary phase nucleation rose with increasing the amount of mischmetal addition,while the minimum temperature and growth temperature of the eutectic reaction both increased firstly and then decreased.Consequently,the temperature difference of the eutectic recalescence fluctuated.The addition of mischmetal decreased the room temperature strength,but improved the elevated temperature strength and elongation of AZ91D alloy.更多还原