Abstract
The effects of calcium oxide (CaO) particle size on the microstructure and properties of AZ91 alloy were investigated using commercial AZ91 (Mg-9Al-1Zn, wt%) alloy and CaO nano (50 nm), sub-micro (200 nm, 500 nm) and micro (1000 nm) particles as grain refiners. The results showed that the grain size of AZ91 alloy decreased non-linearly with the increase of CaO particle size from nano to micro. When the particle size was sub-micro (500 nm), the grain size decreased from 167.8 µm to the lowest value of 33.7 µm. Due to the in-situ replacement reaction between CaO and Mg matrix, a newly formed Al2Ca phase distributed uniformly, consuming elemental Al, which greatly reduced the content of the β-Mg17Al12 phase. As a result, AZ91-CaO500 nm alloy has relatively high mechanical properties and corrosion resistance. In addition, the research revealed that nano-CaO particles were too small to melt into AZ91 alloy completely and undissolved CaO particles residual in the form of a mixed aggregate, resulting in lower mechanical properties and corrosion resistance of AZ91-CaO50 nm alloy compared with AZ91-CaO500 nm alloy, and even lower than other alloys in this study.
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