Microstructure of Al-4.99Zr-1.1B Master Alloy and Its Grain Refinement Effect on AZ31 Magnesium Alloy

An Al-4.99Zr-1.1B master alloy was fabricated by in-situ synthesis from Al melt and K2ZrF4+KBF4 mixed powder. The microstructure of the Al-4.99Zr-1.1B master alloy and its grain refinement effect on AZ31 magnesium alloy were studied by XRD, OM, SEM and EDS. Results show that a large number of fine ZrB2 particles can be observed in the Al-4.99Zr-1.1B master alloy. With increasing the addition amount of Al-4.99Zr-1.1B master alloy, the primary α-Mg grains of AZ31 magnesium alloy are further refined and the network structure of the intermetallic β-Mg17Al12 phase is changed into small blocky structure. Upon adding 0.6% Al-4.99Zr-1.1B master alloy, the average size of primary α-Mg grains is reduced from 170 μm to 45 μm. The present results indicate that the ZrB2 particles can act as the effective heterogeneous nuclei of α-Mg grains and is responsible for the grain refinement of AZ31 magnesium alloy.