Effect of Al-4B Master Alloy on Grain Size and Mechanical Properties of AZ31 Magnesium Alloy

Al-4B master alloy was prepared by reaction of KBF₄ with molten aluminum. The effects of Al-4B master alloy with different mass fraction (0%-2.0%) as inoculant on grain size and mechanical properties of AZ31 magnesium alloy were studied. The results show that Al-4B master alloy was composed of AlB₂ and α-Al phase. The addition of Al-4B master alloy could obviously refine the grain of AZ31 magnesium alloy, improve the uniformity of grain size and reduce the porosity. The grain refinement effect was the most obvious when the mass fraction of Al-4B master alloy was 1.0%. With increasing Al-4B master alloy content, the hardness, tensile strength, yield strength and percentage elongation after fracture of AZ31 magnesium alloy increased. The yield strength and grain size were in accordance with Hall-Petch relation. The improvement of mechanical properties of AZ31 magnesium alloy was mainly related to the fine grain strengthening, dispersion strengthening caused by AlB₂ phase and the decrease of porosity of casting microstructure.