An entrainment defect (also known as a double oxide film defect or bifilm) acts a void containing an entrapped gas when submerged into a light-alloy melt, thus reducing the quality and reproducibility of the final castings. Previous publications, carried out with Al-alloy castings, reported that this trapped gas could be subsequently consumed by the reaction with the surrounding melt, thus reducing the void volume and negative effect of entrainment defects. Compared with Al-alloys, the entrapped gas within Mg-alloy might be more efficiently consumed due to the relatively high reactivity of magnesium. However, research into the entrainment defects within Mg alloys has been significantly limited. In the present work, AZ91 alloy castings were produced under different carrier gas atmospheres (i.e., SF₆/CO₂, SF₆/air). The evolution processes of the entrainment defects contained in AZ91 alloy were suggested according to the microstructure inspections and thermodynamic calculations. The defects formed in the different atmospheres have a similar sandwich-like structure, but their oxide films contained different combinations of compounds. The use of carrier gases, which were associated with different entrained-gas consumption rates, affected the reproducibility of AZ91 castings.

夹带缺陷（也称为双氧化膜缺陷或双膜）在浸入轻合金熔体中时会形成包含夹带气体的空隙，从而降低最终铸件的质量和再现性。以前用铝合金铸件进行的出版物报道，这种捕获的气体随后会被与周围熔体的反应消耗掉，从而减少空隙体积和夹带缺陷的负面影响。与铝合金相比，由于镁的反应活性较高，镁合金中的夹带气体可能被更有效地消耗掉。然而，对镁合金夹带缺陷的研究受到了很大的限制。在目前的工作中，AZ91合金铸件是在不同的载气气氛（即SF ₆ /CO₂，SF ₆ /空气）。根据显微组织检查和热力学计算，提出了AZ91合金夹带缺陷的演变过程。在不同气氛中形成的缺陷具有类似的三明治结构，但它们的氧化膜含有不同的化合物组合。载气的使用与不同的夹带气体消耗率有关，影响了 AZ91 铸件的再现性。