Sr对碳质孕育Mg-3%Al合金熔体中Fe致晶核毒化与衰退的抑制作用

利用碳和Sr对Mg-3%Al(质量分数)合金进行复合孕育处理,引入杂质Fe并调整孕育保温时间,研究杂质Fe对孕育细化效果和晶核结构特性的影响。结果表明:碳和Sr复合孕育可有效细化Mg-3%Al合金,杂质Fe添加及添加顺序对孕育效果影响较小,长时间保温后晶粒尺寸略有增大。延长保温时间至80 min,晶粒尺寸最大从560μm一直稳定在100~130μm之间,其细化率保持稳定,变化幅度不大。Sr存在可有效抑制Fe对碳质孕育细化效果的粗化和加速孕育衰退的不利影响。晶核结构观测表明孕育合金中主要存在Al4C3颗粒和Al-Fe相表面包覆Al4C3相的双相颗粒,两者均可以作为α-Mg晶粒的有效形核核心。Sr易于朝颗粒表面偏聚和富集,从而降低颗粒表面能和相间的界面能,促进双相结构颗粒的生成,并可抑制晶核组分和结构变化,提高晶核结构稳定性,从而有效抑制晶核毒化和孕育衰退。

Inhibiting behavior of Sr on nuclei poisoning and fading of Mg-3%Al melt inoculated by carbon

The Mg-3%Al melt was inoculated by carbon combining with Sr addition.The trace impurity Fe was introduced into the melt and the holding time after carbon-inoculation was adjusted.The effect of impurity Fe on grain refinement and structure characteristics of the nucleating particle was studied by adjusting the sequence of Fe introduction and holding time.The results show that the Mg-3%Al alloy is significantly refined by carbon inoculation combining with Sr addition.The addition of impurity Fe and its sequence have a little adverse effect on the grain refinement.The grain size is refined from 560μm to the range between 100 and 130μm.The grain size after being inoculated increases slightly with increasing the holding time to 80 min.The presence of Sr can effectively inhibit the adverse effects of Fe-induced grain coarsening and accelerating the fading of carbon inoculation.There are two types of particles which could be easily observed in the inoculated Mg-3%Al alloy containing with trace Fe impurity.One is the Al4 C3 particles and the other is dual-phased particles of Al-Fe phase coated with Al4 C3.Both of the particles should be the potent nuclei ofα-Mg grains.Higher Sr content in the particles was measured.Active element Sr easily segregates and is enriched towards the surface of particles,reducing the surface energy and interfacial energy of particles.The segregation of Sr can promote the formation of dual-phase particles and improve the stability of potent nuclei.Consequently,the Fe-induced nuclei-poisoning and the fading of inoculation can be effectively inhibited due to Sr addition in the carbon-inoculated Mg-Al melt.