密封熔炼炉中空气分压对镁合金保护效果的影响

Effect of Partial Pressure of Air in HFC134a/N_2/Air Atmosphere on Protection of Magnesium Alloy in a Sealed Smelting Furnace

在一次性充入0.01%(体积分数)HFC134a/N2/空气保护气氛的密封熔炼炉中,研究了气氛中空气含量、表面搅拌和保温时间对AZ91D镁合金在760℃下保护效果的影响和气氛对熔炼坩埚内壁的腐蚀情况,并对表面膜形貌、厚度和成分进行了研究。研究结果表明,气氛中空气分压为8.0kPa时,经过10h保温,AZ91D熔体依然被保护,表面搅拌不影响保护效果。随着气氛中空气分压从2.3kPa增加到80.0kPa,AZ91D表面平整度降低,当空气分压为80.0kPa时,表面膜分为两层,最表层呈网状;表面膜中氧的原子分数从11.98%升高到26.62%,C的原子分数从0.98%降低到0,表面膜厚度从1.1μm增加到1.7μm,熔炼坩埚内壁从没有红锈腐蚀到大片氧化铁皮脱落。因此在密封熔炼炉含0.01%(体积分数)HFC134a气氛中熔炼AZ91D,气氛中空气含量越少,金属镁的氧化量越少。

The mixed gas of 0.01 %(volume fraction)HFC134a/N2/air was fed into a sealed smelting furnace once,for the protection of AZ91D magnesium alloy subjected to smelting in the furnace.The influences of the air partial pressure in the mixed gas,stirring of the smelted Mg alloy,and holding time of smelting on the protection outcome of the Mg alloy smelted at 760℃ were investigated,while the corrosiveness of the mixed protective gas to the inner wall of the smelting crucible was examined.Moreover,the morphology,thickness,and composition of the surface film of the smelted Mg alloy were analyzed.The results showed that at an air partial pressure of 8.0 kPa the mixed atmosphere had good protection to the AZ91D alloy smelted at 760℃,for a holding time of 10 h,and the protection was not affected by surface agitation.With the increase of the air partial pressure from 2.3 kPa to 80.0 kPa,the smoothness of the smelted Mg alloy decreased,the content(atom fraction)of 0 in the surface of the smelted Mg alloy Journal of Materials Protection increased from 11.98% to 26.62% and that of C decreased from 0.98% to 0,accompanied by the increase in the thickness of the film from 1.1 μm to 1.7 μm and the transformation from the absence of red-rust corrosion on the inner wall of the furnace to large flakelike peeling of iron oxide.When the air partial pressure rose to 80.0 kPa,the corresponding smelted Mg alloy was characterized by twolayer structure,and the top layer was dominated by loose reticulation-like structure.Therefore,it was suggested to control the air partial pressure of the mixed 0.01 % HFC134a/N2/air atmosphere in the sealed smelting furnace at a rationally low level so as to get rid of severe oxidation of the Mg alloy.