Existing forms of Gd in AZ91 magnesium alloy and its effects on mechanical properties

AZ91 -xGd (x = 0, 0.3, 0.6, 0.9 wt%, mass fraction) magnesium alloy specimens were prepared by die casting, the main existing forms of rare earth Gd in AZ91 magnesium alloy at different cooling rates and their effects on microstructure and room temperature tensile properties were investigated. The results show that rare earth Gd exists in AZ91 magnesium alloy mainly in the forms of Al2Gd phase and a small amount of solid solution in magnesium matrix, and it can refine the grain of alloy, reduce the number of beta-Mg17Al12 phase and make it disperse. Gd can improve the room temperature strength of alloy by solution strengthening, fine grain strengthening and decreasing the weakening effect of beta-Mg17Al12 as a crack source. However, the strength of alloy can be reduced by the formation of Al2Gd which is easy to crack. The cooling rate of the alloy affects the solid solution quantity of Gd, the grain size of alloy, the amount of Al2Gd phase and the amount and distribution of beta-Mg17Al12, thus the effects of Gd on the microstructure and properties of the alloy were affected. In this experiment, when the Gd content is 0.62%, the cooling rate is 39.6 degrees C.s(-1) , the comprehensive mechanical properties of alloy are the best, the tensile strength is 248.67 MPa, the elongation is 3.4%.