在预先装入固态MgF2的密封熔炼炉中,研究了熔炼温度和炉内空气含量对AZ91D镁合金保护效果的影响,并对表面膜形貌、成分和成分分布进行了研究.结果表明:保护效果随熔炼温度和气氛中空气含量增加而逐渐变差;当气氛中空气体积分数为25%,实验温度＜750℃时,AZ91D镁合金很好被保护;当熔炼温度为650℃,气氛中空气体积分数＜30%时,AZ91D镁合金很好被保护.所有表面膜由MgF2和MgO组成,表面膜厚度随熔炼温度和气氛中空气含量的增加而增加,表面膜中MgF2的数量也随熔炼温度和气氛中空气含量的增加而显著增加;膜表面平整度随气氛中空气含量的增加而变差,熔炼温度增加对膜平整度影响不大.固态MgF2在熔炼温度下蒸气压较高,其蒸气与空气中氧气一起参与AZ91D镁合金表面膜的形成.
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