Ca-Y复合变质对高硅Mg-Si-Zn合金组织与性能的影响

Effects of Ca-Y compound modification on microstructure and properties of Mg-Si-Zn alloy with high Si content

为提高高硅Mg-Si-Zn合金的性能,实验通过调整Ca、Y变质剂的含量,研究在Ca变质、Ca-Y复合变质作用下高硅Mg-Si-Zn合金的凝固组织与性能。结果表明:在Mg-4Si-4Zn合金中加入Ca,可使合金凝固组织中初生Mg2Si相由粗大的枝晶形貌转变为细小的矩形块状形貌,共晶组织由粗大的汉字状转变为点棒状;当Ca加入量为0.7%时(质量分数)变质效果最为明显;当Ca加入量超过0.7%后,合金中会形成CaMgSi棒状相,这是Ca变质效果下降的一个主要原因。当合金中Ca加入量为0.7%时,再加入Y会将初生Mg_2Si相由规则平整形貌转变为带有沟壑孔洞的复杂形貌,而相的尺寸基本不发生改变,这使得经Ca-Y复合变质的Mg-4Si-4Zn合金的硬度显著高于Ca单一变质合金的,硬度提高超过10%。

By changing the addition of Ca and Y,the solidified microstructure and properties of Mg-Si-Zn alloy with high Si content were investigated under the condition of Ca modification and Ca-Y compound modification.The results show that,the Ca addition in to Mg-4Si-4Zn alloy has obvious modification effect,with the primary phase morphology of Mg2Si transforming from big dendrite to small regular square block and the morphology of eutectic Mg2Si changing from complex Chinese pattern to point bar.The most obvious effect of modification is near the Ca addition of 0.7%(mass fraction),and CaMgSi bar phase will precipitate from the alloy melt while Ca addition is more than 0.7%,reducing the Ca modification.When the Ca addition is 0.7%,the primary Mg2Si transforms from regular square to complex morphology with ravine holes without the obvious change of phase size by the Y addition.The alloy hardness after Ca-Y compound modification is obviously higher than that after Ca modification,with the hardness increasing by more than 10%.