Regulation mechanism of cooling rate and RE (Ce, Y, Gd) on Mg17Al12 in AZ91 alloy and it's role in fracture process

Abstract

AZ91-xRE(Ce, Y, Gd, x = 0, 0.3, 0.6, 0.9) alloys with different cooling rates were prepared by die casting. Effects of cooling rate and rare earth elements (Ce, Y and Gd) on Mg17Al12 compound in the alloy and the role of Mg17Al12 compound in fracture process were studied. The results show that the Mg17(Al, Zn)12 compound will be formed in AZ91 alloy, the cooling rate and rare earth elements (Ce, Y and Gd) both can regulate the size, distribution and content of Mg17Al12 compound. The cooling rate can regulate the size and distribution of Mg17Al12 compound in the alloy, but has less effect on the content of Mg17Al12 compound. The addition of rare earth elements can significantly reduce the content of Mg17Al12 compound and refine its size. The reduction effect of Ce on the content of Mg17Al12 compound in alloy is the largest, and the size optimization effect is also the most significant. The effects of Y are the second, and the effects of Gd are relatively poor. The Mg17Al12 compound in alloy is the main crack source and important crack propagation path because of its large size and low strength. Increasing the cooling rate and adding rare earth elements Ce, Y and Gd can make Mg17Al12 compound play a better role in second phase strengthening by optimizing the size, distribution, and content of Mg17Al12 compound.

Keywords

• Magnesium alloy
• Mg17Al12 compound
• Rare earth elements
• Cooling rate
• Microstructure regulation