Abstract:

The influence of MgCO₃ on the microstructure of AZ31 magnesium alloy has been investigated.The results show that the morphology of β-Mg₁₇Al₁₂ Phase in the alloy changed from continuous network to diseontinuous one, and their amount deereased with inereasing MgCO₃ content. AZ31 magnesium alloy has the best refining effect when the AZ31 magnesium alloy with addition of 0.6% MgCO₃ in 760 ℃, the average grain size of the α-Mg grain decreases from about 570 μm of AZ31 base alloy to 100μm, the reduced extent is about 82.5%, tensile strength are improved by 57.9%, the elongation percentage increases to 11.1%. Based on the analysis of EDS, Ebind and Gibbs free energy, the mechanism of grain refiner was generation of Al₄C₃ that can be used as crystallization center of the Mg when MgCO₃ added. Due to the generation of Al₄C₃ in AZ31 magnesium alloy, the grain boundary is pined and the grain growth is limited.The Al element was quickly pushed to the grain boundary along with the solid/quid interface, and generated the β-Mg₁₇Al₁₂ phase along the grain boundary which has an effect of immobilizing the grain boundaries. The distribution of alloying elements have changed.

Key words: metallic material, AZ31, MgCO₃, grain refinement, Al₄C₃