Effect of Rare Earths on Hot Cracking Resistant Property of Mg-Al Alloys
来源期刊：JOURNAL OF RARE EARTHS2006年第3期
论文作者：Guo Xutao Zeng Daben Zheng Weichao Tang Bin Li Shuangshou
Key words：Mg-Al alloys; hot cracking; rare earths;
Abstract: 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 MgAl 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 α-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.
Guo Xutao1，Zeng Daben1，Zheng Weichao2，Tang Bin3，Li Shuangshou2
(1.Department of Mechanical Engineering;
2.Fundamental Industry Training Center;
3.Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China)
Abstract: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 MgAl 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 α-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.
Key words:Mg-Al alloys; hot cracking; rare earths;
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