Ce及铜模快冷对AZ91合金组织及热稳定性的影响

Grain Refinement and Thermal Stability of Copper-mould Chilled Magnesium Alloy Containing Rare Earth Ce

采用铜模喷铸与等温热处理相结合,对比研究不同冷速及固溶处理条件下稀土Ce在AZ91镁合金中的存在形式及稀土相的演变行为,揭示Ce对快冷镁合金组织的细化及热稳定性的影响。结果表明,稀土Ce在凝固界面前沿富集,抑制晶粒生长并促进形核,导致镁合金组织细化,但含量过高时会形成针状Al_(11)Ce_3相,降低成分过冷,不利于组织细化。由于过冷度的增加及凝固潜热对形核抑制影响的减弱,铜模喷铸镁合金晶粒细化显著,并且过饱和固溶体的形成可有效避免针状稀土相的形成。经420℃固溶处理后,颗粒状Mg_(12)Ce化合物的析出可有效抑制高温晶粒长大,提高快冷镁合金细晶组织的热稳定性。

Adopting copper mould spray casting combining with isothermal heat treatment,the existingform of rare earth Ce in AZ91 magnesium alloy with different cooling rate and its evolution behavior during solid solution treatment were analyzed.The influences of Ce on microstructure refinement and thermal stability of rapid cooled magnesium alloy were analyzed.The results show that Ce is enriched ahead of the solidification interface,which suppresses the grain growth and promotes nucleation.Consequently,grain refinement is achieved in magnesium alloy.However,accicular Al11Ce3 phase can be generated in the higher Ce content alloy,which reduces constitutional undercooling and harmful to refinement.Due to the increase of undercooling and the relief of inhibition effect of nucleation by latent heat,the grain refinement of spray casted alloy presents remarkable,and formation of the accicular rare earth phase can be avoided effectively by formation of supersaturated solid solution.After solid solution treatment at 420℃,the precipitation of fine granular Mg12Ce compounds can inhibit the grain growth at high temperature,which improves the thermal stability of fine grain structure in rapidly cooled magnesium alloys.