椭圆旋扭管反复凝熔法制备半固态A356铝合金浆料

Preparation of semi-solid A356 Al alloy slurry by repeated heating-cooling method with elliptical-twisted tubes

采用椭圆旋扭管反复凝熔法制备半固态A356铝合金浆料。结果表明:椭圆旋钮管反复凝熔技术具有旋扭强制对流促进初生晶核游离、自搅拌加强熔体剪切、反复凝熔促进形核的作用,可使初生α晶核演变为球形或近球形晶粒。椭圆管长短轴比、旋扭强度以及凝熔频率对半固态浆料的微观组织有显著影响。随着长短轴比、旋扭强度和凝熔频率的增大,晶粒细化和圆整效果显著提高;但长短轴比过大,容易堵塞流道;当旋扭强度超过13.5(°)/cm时,晶粒细化和圆整效果没有明显提高;当凝熔频率超过40μm-1时,晶粒细化作用不再增强,圆整度反而降低。在椭圆长短轴比为1.8-1、旋扭强度为13.5(°)/cm、凝熔频率为40μm-1的条件下可制得晶粒直径细小、形状圆整的半固态浆料。

The semi-solid slurry of A356 aluminum alloy was prepared by the repeated heating-cooling method with the elliptical-twisted tubes.The results indicate that by the repeated heating-cooling method with elliptical-twisted tubes the microstructures of primary grains are transformed from dendritic or rosette-shaped to fine net-globular under the action of grains detachment due to the forced convection,shear caused by self-stirring and heterogeneous nucleation because of repeated heating/cooling.The axial ratio,twisting strength and heating-cooling frequency have significant influences on the microstructure of the semi-solid slurry.With the increase of axial ratio,twisting strength and heating-cooling frequency,the grain refinement and sphericity of particles have remarkable improvement.However,at the twisting strength over 13.5(°)/cm and heating-cooling frequency over 40 μm-1,the grain refinement does not have a much improvement and the sphericity decreases on the contrary.At the axial ratio of 1.8:1,twisting strength of 13.5(°)/cm and heating-cooling frequency of 40 μm-1,the favorable microstructure of semi-solid A356 aluminum alloy can be generated by the repeated heating-cooling method with the elliptical-twisted tubes.