MgCO_3对AZ31镁合金晶粒的细化

研究了MgCO3对AZ31镁合金凝固组织的影响。结果表明:随着MgCO3的增加,合金中的β-Mg17Al12相由晶内分布变为晶间分布。在AZ31中添加0.6%的MgCO3,于760℃时保温10min,细化效果最佳。α-Mg晶粒的尺寸由基体合金的570μm降至100μm,降低幅度约为82.5%,抗拉强度提高了57.9%,延伸率约提高了11.1%。通过能谱分析,结合能计算及自由能计算证实,细化机理是MgCO3反应后生成的部分Al4C3质点作为异质核心细化晶粒。多余的Al4C3质点钉扎晶界阻碍晶粒长大。Al元素随固/液界面前沿被快速推至晶界,生成沿晶界生长的β-Mg17Al12相,起到进一步固定晶界的作用。合金元素的分布均有改变。

Refinement effect of MgCO_3 in AZ31 magnesium alloy

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.