真空感应电磁悬浮熔炼对A356铝合金组织和性能的影响

Impact of Vacuum Induction Electromagnetic Levitation Melting on Microstructure and Properties of A356 Alloy

优化A356铝合金的组织和性能成为实现汽车轻量化、节能化、舒适化和多样化发展的需求之一。为进一步挖掘A356铝合金的性能潜力,本研究采用能量密度高、清洁和可控性好的真空感应电磁悬浮熔炼技术对其进行细化变质处理,并与常规复合细化变质处理进行对比。试验结果表明,真空感应电磁悬浮熔炼复合细化变质处理可使铝合金中的共晶硅相由粗大的板片状转变为细密的球形颗粒状,并在晶界均匀析出;α-Al相明显细化,呈规则圆整的等轴晶状。在真空感应电磁悬浮熔炼工艺条件下,形核功ΔG^*的贡献远大于扩散激活能ΔG A;过冷度不会出现极大值;形核率I随过冷度ΔT的增加而急剧增大,实现熔体爆发生核。同时,晶粒之间强烈的互相碰撞、对流运动致使枝晶臂被剪切而折断、破碎与增殖,导致形核率I更大,并最终遗传到凝固组织中。因此,真空感应电磁悬浮熔炼技术对A356铝合金的细化变质效果较常规工艺有显著提升,且所得合金具有更好的力学性能。

It is generally one of the critical demands for developing light-weight, energy-saving, comfortable and diversified automobiles to optimize the microstructure and mechanical properties of A356 aluminum alloy. For further tapping the property potential of A356 aluminum alloy, the refinement and modification of the alloy was conducted by vacuum induction electromagnetic levitation melting, a clean and well controllable techno-logy with high energy density, and the comparison in treatment efficiency between the adopted approach and the conventional one was carried out as well. In light of the experimental results, vacuum induction electromagnetic levitation melting would facilitate the convert of the eutectic silicon phase from coarse and needle-like to fine spherical particles, and the particles were uniformly precipitated at the grain boundaries.α-Al phase was also significantly refined, presenting the regular rounded equiaxed crystal. During the process of vacuum induction electromagnetic levitation melting technology, nucleation work Δ G^* made far more contribution than diffusion activation energy Δ G A. There was no peak value for supercooling degree. The nucleation rate I skyrocketed as the supercooling degree Δ T went up, giving rise to the burst nucleation of the melt. Meanwhile, the sheared, broken, crushed and proliferated dendrite arms induced by violent collision and convective motion between the grains enlarged the nucleation rate I , which eventually inherited into the solidified structure. Consequently, vacuum induction electromagnetic levitation melting exhibited superior refining and modification effect to conventional technique, and better mechanical properties of A356 aluminum alloy can be obtained as well.