An Al-5Zr-1.1B grain refiner was prepared by in-situ synthesis from Al melt and K2ZrF4+KBF4 mixed powder. The microstructure of Al-5Zr-1.1B grain refiner was analyzed by XRD, SEM and EDS. The effect of Al-5Zr-1.1B grain refiner on the microstructure and mechanical properties of AZ91D magnesium alloy were studied. Results show that a large number of fine ZrB2 particles were observed in the Al-5Zr-1.1B grain refiner and the ZrB2 particles could act as the heterogeneous nuclei of α-Mg grains. With the increase of the addition amount of Al-5Zr-1.1B grain refiner, the α-Mg grains of AZ91D magnesium alloy were refined from coarse dendrites to equiaxed grains. When the addition amount of Al-5Zr-1.1B grain refiner increased to 0.6%, the α-Mg grains of AZ91D magnesium alloy were refined to fine equiaxed grains with an average diameter of 45 μm, and the tensile strength and elongation of AZ91D magnesium alloy were improved to 195.3 MPa and 3.94%, respectively. The α-Mg grains average diameter of AZ91D magnesium alloy decreased by 73.5% and the tensile strength and elongation improved by 25.9% and 27.9% compared with that of AZ91D magnesium alloy without adding the Al-5Zr-1.1B grain refiner. It is concluded that the Al-5Zr-1.1B is an effective grain refiner to refine the α-Mg grains of AZ91D magnesium alloy.
Microstructure and mechanical properties of AZ91D magnesium alloy by expendable pattern shell casting with different mechanical vibration amplitudes and pouring temperatures
