电磁离心铸造Al-20Si过共晶合金中硅相组织演变规律

采用电磁离心铸造的方法制备了Al-20Si(质量分数,下同)过共晶合金空心管坯,研究了电磁场对合金凝固组织及硅相形貌的影响.结果表明,随磁场强度增加铸坯外侧硅相聚集层厚度不断减小;与传统离心铸造的铝硅过共晶合金微观组织相比,施加电磁场后凝固组织中初晶硅相得到细化,外侧硅相形貌逐渐由典型的五瓣星形成为沿热流方向生长的初晶硅枝晶,内侧硅相受到电磁搅拌作用发生合并凝聚和钝化;初晶硅相尺寸及形状因子随磁场强度增加在不断减小.电磁搅拌破坏了硅相呈放射状排列的结构,共晶硅分布杂乱,且共晶团共晶片层间距逐渐增加.

Microstructure Evolution of Primary Si Phase in Hypereutectic Al-20Si Alloys Prepared by Centrifugal Casting under an Electromagnetic Field

Hypereutectic Al-20Si (mass fraction) alloy hollow tubes were prepared by centrifugal casting under an electromagnetic field (EMF). Effects of EMF on the solidification microstructure of the alloy and morphology of primary Si phases were investigated. Results show that primary Si phases in the solidification microstructure were refined after applying EMF compared with the microstructure of the Al-20Si hypereutectic alloys by conventional centrifugal casting. The segregation layer width of Si phases in the outer of the tube decreased gradually with the increase of the EMF intensity. The morphology of the Si phases in the outer of the tube changed from typical pentagram into dendrites grown along the heat flow direction. The phenomena of dulling and congregation of the Si phases in the inner of the tube were found due to EMF stirring. The size and aspect ratio of the primary Si phase decreased little by little with the increase of EMF intensity. The electromagnetic stirring destroyed the radial configuration of Si phases, eutectic Si phases distributed randomly, and the eutectic lamina spaces in the eutectic cell increased gradually.