Study on Fe reduction in AZ91 melt by B2O3

Abstract This article studies the effects of B 2 O 3 on the reduction of Fe content in scrap AZ91. The Fe concentration in a scrap can be decreased to less than 0.001 wt.% when the scrap melt is refined by a B 2 O 3 -containing flux. Experimental results suggest that the best effect can be got when the B 2 O 3 addition is 0.61 wt.% of the melt. Optimal process temperature and holding time are 735 °C and 2400 s, respectively. Microstructures of the B 2 O 3 -processed samples were investigated by OM, SEM, EDS. Immersion corrosion tests were conducted to study the corrosion resistance. Homogeneous precipitations of a kind of Mg–Al–C–O particles were observed in the refined samples. These particles can refine grains and in turn improve the mechanical properties of the alloy. B 2 O 3 processing reduced the immersion corrosion rate from 15 to 0.3 mg cm −2 per day. The mechanism of Fe reduction by B 2 O 3 processing is analyzed thermodynamically. Formation of FeB and settling of it into melting sludge are suggested to be the primary mechanism of Fe reduction by B 2 O 3 processing.