稀土对Mg_2Si/AZ91D复合材料中Mg_2Si相的影响

Effect of RE,Yttrium on Morphology of Primary Mg2_Si Phases in Mg_2Si /AZ91D Composites

研究了不同含量的富La混合轻稀土(RE)和钇(Y)对Mg2Si/AZ91D复合材料中初生Mg2Si相形貌的影响。结果表明,混合轻稀土RE和Y对Mg2Si/AZ91D复合材料中的初生Mg2Si相均有明显的细化变质效果,但Y对初生Mg2Si相的细化变质效果优于等量混合轻稀土。合金液经0.8%的混合轻稀土RE或Y变质后,初生Mg2Si相由粗大的树枝状转变为细块状或颗粒状;当RE或Y加入量达到1.2%时,均出现过变质现象,初生Mg2Si相再次明显粗化。其变质机理主要与RE、Y和它们的化合物富集于Mg2Si相生长表面,从而抑制其生长有关。

Effects of different contents of RE（rich La） or Yttrium on morphologies of primary Mg2 Si pha- ses in MgzSi/AZ91D composites were investigated. The results show that RE and Yttrium can all effec- tively refine the primary Mg2 Si phases in Mg2 Si/AZ91D composites, and the modification effect of Yttri- um is superior to that of RE. Morphologies of the primary MgzSi phases are changed from coarse den- drites to fine polygonal particles with 0.8% RE or Yttrium addition. Over-modification of the primary Mg2 Si phases can be observed with RE or Yttrium addition to 1.2 %, and primary Mg2 Si phase is coars- ened again. Modification mechanism is attributed to the enrichment of RE ,Yttrium and their intermetal- lic compounds on the growth faces of the primary Mg2Si crystals restraining the growth of primary phase.