熔态Mg在Air/SF6保护气氛中形成的表面膜特征

研究了熔态Mg在Air/SF6保护气氛中形成的表面膜特征.随着镁液在保护气氛中暴露时间的增加,表面膜中F原子分数逐渐增加,而O的原子分数基本不变.因此认为保护性表面膜形成后,主要为F和Mg发生反应.部分近表面区域场发射SEM断面图中有多个不连续的白亮富F(约为74%原子分数)小半圆区域,而富F的小半圆亮区之间F含量显著降低(约为4.98%);部分为一条厚度不均匀的白亮带,其中F原子分数也很不均匀.随着暴露时间的增加,表面的结晶粒度逐渐增加.冷却凝固后的表面有很多裂纹,这些裂纹的形成可能是由于表面MgO膜疏松,晶粒不断长大收缩,快速凝固过程中,MgO膜下面的镁液凝固收缩而形成.

Characterization of Surface Films Formed on Molten Magnesium with Air and SF6 as Protective Gases

The characterization of surface films of magnesium melt protected by air and SF_6 gases was studied. As the exposure time increases, the atom fraction of fluorine in surface films increases, while the atom fraction of oxygen almost keeps unchanged. Therefore, the reaction between magnesium and protective gases should mainly happen between magnesium and fluorine after the initial film is formed. The SEM observations of the cross section of the surface films show that there are some discontinuous small semicircular white spots which contain about 74% atom fraction in some near surface zone; and there are some white cingula with different thickness in the other near surface zone with distinct uneven fluorine content. The crystal size in surface films increases with the increase of the exposure time under protective atmosphere. Many cracks appear on the surface films of the solidified magnesium, these cracks may result from the shrinkage of surface film with crystal growing up and the shrinkage of bulk magnesium when the temperature lowers down.