2022 Volume 72 Issue 11 Pages 631-637
Initial stages of the refractory degradation process by molten Al-5Mg alloy were investigated by analyzing the degradation structures caused by an interaction with molten metal during heat cycles. The refractory aggregate, found to be poly-crystalline, consisting of cristobalite (SiO2) and mullite (Al6Si2O13), was deteriorated ahead of the surrounding matrix. Metal permeated into the refractory, forming a thin metal layer along the crucible surface below the molten metal line at an early stage of degradation process, which would later serve as the bases for the metal infiltration path through the refractory above the molten metal line. A discontinuous film (thickness<3μm), most likely MgAl2O4, was formed at the “melt / refractory” interface. At the experimental temperature of 1150°C, Mg in the molten metal would build up as Mg gas at MgAl2O4 film/refractory interface and easily diffuse into the aggregate body and react with the aggregate components of SiO2 and Al6Si2O13 to form MgAl2O4 and Al-Mg-Si-O compounds. This was followed by the molten metal infiltration into the refractory while reducing the Al-Mg-Si-O compound to form MgAl2O4. Through the initial degradation process MgAl2O4 would finally form in a successive chain of reactions, resulting in deterioration of the crucible.
