RE对铝合金表面氧化膜保护效果的影响

采用减压凝固试验法，研究了RE对A356铝合金熔体氢含量的影响规律。通过X射线衍射、扫描电镜等分析了RE对A356铝合金表面氧化膜成分及形貌的影响。结果表明，A356合金中加入一定量的RE后，熔体氢含量显著降低。加入RE后，表面氧化膜出现大量RE氧化物和铝氧化物形成的LaAl11O18的复合氧化物，这种复合氧化物使铝合金表面氧化膜更加致密。扫描电镜分析表明，不加RE的氧化膜表面凹凸不平，有明显开裂后愈合的痕迹，而添加RE后，表面比较平整，致密度显著增加，几乎没有看到开裂的现象，这大大减少了新鲜的铝液暴薅在空气中的几率，降低了熔体中的氢含量。

Influence of Strontium and Rare Earth Elements on the Surface Oxide Films Protective Effect of A356 Aluminum Alloy Melt

Effects of Re modification and Sr modification on constituent and morphology of surface oxidized film of A356 aluminum alloy have been observed by X-ray and SEM.The influential mechanism of Re modification and Sr modification on hydrogen content in A356 melt has been understood from view of compactness and completeness of surface oxidized film.The results indicate that compound LaAl_ 11O_ 18 was formed on surface oxidized film on Re modified A356 alloy,which makes surface oxidized film more compact and very flat with almost no-crack defects to effectively prevent reaction of Al from water.While a large number of compound SrAl_2O_4 was formed on the surface oxidized film of Sr modified alloy,which deteriorates the compaction of surface oxidized film to generate amounts of track from crack in the surface oxidized film to greatly promote the reaction between Al and water due to the fresh liquid Al continuously exploding over air,resulting in the sharp increase of hydrogen content in the melt.