Ce对AZ91镁合金铸态组织细化的影响

INFLUENCE OF CERIUM ADDITION ON AS-CAST MICROSTRUCTURE REFINEMENT OF AZ91 MAGNESIUM ALLOY

加入少量的Ce(0．2％-0．8％,质量分数)可明显细化α-Mg基体,随Ce量增加,合金中的β-Mg17Al12相数量减少,且由连续网状形态变为非连续分布．同时, Ce与合金中的Al结合形成针状或杆状的Al4Ce化合物．能谱分析和液淬显微组织观察表明,组织细化机制主要归结为Ce加入引起结晶界面前沿的成分过冷,增加均质形核的数量．显微组织的改善导致了合金的力学性能和腐蚀性能明显提高．

Adding 0.2%-0.8%Ce（mass fraction） in AZ91 magnesium alloy can decrease obviously the α-Mg grain size. The morphology of β-Mg17Al12 phase in the alloy changed from continuous network to discontinuous one, and their amount decreased with increasing Ce content. Meanwhile, the rod-like or needle-like Al4Ce phases mainly distributed at grain boundaries have been observed. EDXS and the observation of water-quenched microstructure showed that the grain refinement mechanism is attributed to the addition of Ce induced the constitution undercooling at solidification interface front, which increased the number of homogeneous nucleation. The mechanical properties and corrosion resistant performance of the alloys containing Ce were improved obviously. KEY WORDS AZ91 magnesium alloy, cerium, microstructure refinement, mechanical property, corrosion