摘要
采用金相光学显微镜(OM)、扫描电子显微镜(SEM)、能谱仪(EDS)和X射线衍射(XRD)等手段,研究了不同Ce含量对Mg-3Al-2. 5Si合金中初生Mg_2Si相的变质效果。结果表明,加入适量Ce可以有效细化初生Mg_2Si相,初生Mg_2Si逐步由"骨骼枝"状和"花瓣"状向细小规则的多边形状转变。Ce的加入量为0. 2%和0. 6%时,对初生Mg_2Si相的变质机理主要以"吸附毒化"机制为主。当Ce加入量为1%时,对初生Mg_2Si相的变质和细化效果最好,尺寸减小到18μm以下。合金基体中形成了大量细小短杆状CeSi_2相,可成为初生Mg_2Si的有效形核核心,此时Ce对初生Mg_2Si的变质有"吸附毒化"和异质形核机制两方面作用;当Ce加入量超过1. 6%时,初生Mg_2Si再次粗化,表现出过变质效果。
Metallographic optical microscope( OM),scanning electron microscope( SEM),energy dispersive spectrum analysis( EDS) and X-ray diffraction( XRD) were used to study the metamorphism effect of the primary Mg_2 Si phase in Mg-3 Al-2.5 Si alloy with different Ce content.Results show that the addition of appropriate amount of Ce element can effectively refine the primary Mg_2 Si phase,and the primary Mg_2 Si gradually changes from the "skeletal branch" shape and the " petal" shape to the fine regular polygonal shape.When the addition amount of Ce is0.2% and 0.6%,the mechanism of metamorphism of the primary Mg_2 Si phase is mainly based on the mechanism of " adsorption poisoning".The optimal metamorphism and refinement effect on the primary Mg_2 Si phase is obtained with addition of about 1% Ce,and the size of the primary Mg_2 Si is reduced to 18 μm or less.A large number of short rod-like Ce Si_2 phases are formed in the alloy matrix,which can be the effective nucleation core of primary Mg_2 Si.At this time,Ce has the effects of"adsorption poisoning"and heterogeneous nucleation mechanism on the metamorphism of primary Mg_2 Si; However,when the addition of Ce exceeds 1.6%,the primary Mg_2 Si is coarsened again and exhibits an over-metamorphism effect.
引文
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