Effect of calcium oxide particle size on microstructure and properties of AZ91 Mg alloy

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 mu m to the lowest value of 33.7 mu m. 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 beta-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 un-dissolved CaO particles residual in the form of a mixed aggregate, resulting in lower mechanical properties and corrosion resistance of AZ91-CaO(50 nm )alloy compared with AZ91-CaO500 (nm) alloy, and even lower than other alloys in this study. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The grain size of AZ91 alloy decreases non-linearly with the increase of CaO particle size. The in-situ replacement reaction between CaO and Mg matrix improves mechanical properties and corrosion resistance, while nano-CaO particles affect the performance of the alloy.