CREM法半连续铸造Al合金非枝晶组织的形成机制

FORMATION MECHANISM OF NON-DENDRITIC STRUCTURE OF ALUMINUM ALLOY PRODUCED BY SEMI-CONTINUOUS CASTING OF CREM PROCESS

研究了低频电磁场作用下７０７５Ａｌ合金半连续铸坯的微观组织 结果表明：铸坯由近球形和蔷薇形晶粒构成，且随磁场强度增大，近球形组织增加，蔷薇形组织减少，整体组织变得细小均匀．这种非枝晶组织的形成机制可解释为：电磁场作用下，从结晶器壁游离的晶粒数量增多，使熔体中的结晶核心增加，此外，游离晶粒随对流熔体一同运动以及晶粒自身的旋转运动抑制了其按枝晶方式生长，从而导致最终形成细小均匀的非枝晶组织．

The microstructure of 7075 Al alloy ingot produced by CREM process under the effect of electromagnetic field with low frequency was studied. The results show that the ingot consists of spheroid-shaped and rosette-shaped grains. With the increase of electromagnetic intensity, the quantity of spheroid-shaped grain increase and rosette-shaped grains decrease. Meanwhile, the microstructure of the ingot becomes more fine and uniform. The formation mechanism of non-dendritic structure can be explained as follows: Under the effects of electromagnetic field., crystal particles are easily dissociated from the crystallizer wall, which increases amount of the grain nuclei in the melt. Furthermore, the movement of free grains together with the melt convection as well as self-rotation of grains restrain them from growing into dendrite, and finally form a fine and uniform., non-dendritic structure.