稀土在铝、镁合金中的应用

稀土元素作为微量元素加入铝、镁合金中,可以净化合金熔体,细化、变质微观组织,减少夹杂.随着稀土元素加入量的增加,可以显著提高铝、镁合金的综合性能特别是高温力学性能.综述了含稀土铝合金和稀土镁合金的研究、发展和应用现状,着重介绍了稀土对铝镁合金冶炼、工艺和合金化的影响.展望了稀土铝、镁合金的发展前景.     

Electron Theory Research in Mg-Y Alloy

Adding yttrium to magnesium can improve the mechanical properties, especially the mechanical behavior at high temperature. The valence electron structures of Mg-Y alloy were analyzed with the empirical electron theory of solids and molecules (EET). Calculation shows that yttrium is on the fifth hybrid level and magnesium is on the third one in pure metal crystals. By comparing with aluminum in Mg-Al alloy, it is shown that the reason why the solution strengthening effect of yttrium is better than that of aluminum in Mg-Al alloy is the enhanced bond energy according to EET. And it is concluded from EET analysis that intermetallies Mg24Y5 can significantly improve the properties of magnesium alloys because yttrium atoms oceupy the centers of the oetahedron and Mg-Y bonds efficiently strengthen the alloy matrix.     

添加混合稀土对纯镁及其合金中元素含量的影响

对纯镁及AZ91D镁合金中添加富铈混合稀土的收得率及其各元素含量的变化规律进行了研究。试验结果表明，混合稀土的收得率随着其添加量的增加而降低，添加适量的混合稀土，纯镁中的混合稀土收得率可达到75％以上，AZ91D合金中的混合稀土收得率可达到90％，以上；镁熔体对混合稀土存在着吸收极限，该试验条件下纯镁的吸收极限为1．6％左右，AZ91D合金的吸收极限为1．9％左右；添加适量的混合稀土可降低纯镁及AZ91D合金中的Cl元素含量至10^-5以下；添加混合稀土会降低镁熔体中的Al含量，对合金元素Zn、Mn以及杂质元素Fe、Cu、Ni、Si的含量不产生影响。     

Effect of Rare Earths on Hot Cracking Resistant Property of Mg-Al Alloys

The effect of rare earths （RE） ranging from 0.1% to 1.2%（mass fraction） on hot cracking resistant property of Mg-Al alloys was investigated. The results show that hot cracking resistant property of Mg-Al alloys remarkably declines with an increase of RE addition. The causes of the decline are as follows： First, grain coarsening of Mg-Al alloys caused by RE addition reduces the fracture strain required for hot crack initiation. Second, RE reduces the eutectic microstructure of Mg- Al alloys, and as a result, shortens the time that the feeding channel remains open, making it difficult to feed the alloy. Furthermore, RE elevates the eutectic reaction temperature, which leads to the decrease in the strength of the interdendritic liquid film at the late stage of solidification. Third, when a-Mg dendrites form continuous skeletons, the interdendritic Al11 RE3 phase tends to block the feeding channels and increases the difficulty of feeding. Last, the shrinkage ratio discrepancy between Al11RE3 phases and α-Mg matrix is prone to cause shrinkage stress and promote hot crack initiation.     

Grain Coarsening Behavior of Mg-Al Alloys with Mischmetal Addition

Small addition of mischmetal （MM） into aluminum alloys can lead to grain refinement. However, it is still uncertain whether the same effect applies to Mg-Al alloys. This work indicated that small amount of mischmetal addition ranging from 0.1% to 1.2% （mass fraction） did not cause grain refinement in Mg-Al alloys. On the contrary, they tended to coarsen the grains. When added into Mg-Al alloys, MM reacted preferentially with Al to form Al11 MM3 phase. As Al11 MM3 phase mainly distributed within α-Mg grains than at grain boundaries, it had little effect in restricting grain growth. In addition, MM reacted with Al8（Mn, Fe）5 or ε-AlMn particles to form Al-MM-Mn compounds, thus it reduced the amount of heterogeneous nuclei in the melt and resulted in remarkable grain coarsening.     

高温相变材料Al-Si合金选择及其与金属容器相容性实验研究

对高温相变材料铝硅合金的相变温度和潜热进行了分析测定,研究了其热稳定性,并对此类相变材料与金属容器的相容性进行了实验研究。实验结果表明,相变材料AlSi12相变温度适中而潜热大,可作为蓄热介质来储存太阳能；温度对AlSi12与不锈钢材料之间的扩散渗透影响显著。     

混合稀土去除再生镁合金中的夹杂

在镁合金废料经过熔剂精炼后,依次添加0.05%～0.9%混合稀土,考察混合稀土对合金液净化效果的影响.结果表明:镁合金液中夹杂的体积分数由0.6%以上降低至0.2%以下.分析认为混合稀土的加入减少了合金液的氧化,反应形成了含稀土氯化物和氧化物的夹杂与镁合金液具有较大的密度差,有利于夹杂的沉降去除.因此,添加适量混合稀土可以起到净化镁合金液的作用.     

稀土耐热镁合金发展现状及展望

介绍了稀土耐热镁合金在俄罗斯、欧美、日本和中国的发展历史及现状。初步讨论了稀土元素对镁合金耐热性能的影响机理。对稀土耐热镁合金的研制开发、应用前景进行了简单分析。     

稀土元素对AZ91D合金晶粒细化的影响

研究了不同混合稀土添加量对AZ91D合金晶粒细化的影响。试验结果表明混合稀土对AZ91D合金有明显的细化效果。当混合稀土的添加量为0．05％(质量分数)时，混合稀土中的Ce，Nd和Pr等在未形成A1-RE化合物之前，大部分以质点的形式弥散分布在AZ91D合金熔体中，可能起到非均匀形核的作用；随着混合稀土添加量的增多，RE优先与Al生成A1-RE化合物，这些化合物大部分偏聚在晶界上，阻碍了晶粒的长大，从而细化了晶粒。     

稀土在耐热镁合金中的应用

本文介绍了稀土对耐热镁合金发展的影响 ,概括了稀土耐热镁合金的发展历史及现状。初步讨论了稀土元素对镁合金耐热性能的影响机理。对稀土耐热镁合金的研制开发、应用前景进行了展望。