铸轧区长度对Al-8Si合金铸轧板显微组织的影响

采用连续铸轧方法制备Al-8Si合金铸轧带坯,利用光学显微镜(OM)、扫描电镜(SEM)和能谱分析(EDS)等手段,研究不同铸轧区长度对铸轧板微观显微组织和中心层偏析的影响。研究表明,随着铸轧区长度的增加,偏析范围先增大、后减小。这是由于铸轧区长度的增加,导致铸轧区域冷却强度加大,较强的冷却速度加快了金属的凝固,从而减轻了中心偏析程度。Al-8Si合金同一铸轧区表层和中心部位共晶硅组织的形貌有较大区别,表层共晶硅呈网状分布,微观形貌大部分呈纤维状,小部分呈瓣片状,中心层共晶硅形貌为沿不同取向的集簇状,形成中间线偏析。这是由于:铸轧坯料在轧制时,上、下表层先与轧辊面接触,而中心层相较于上、下表层的冷却速度较慢,所以,最后凝固,使上、下表层相较于中心层晶粒更加细小。

Influence of length for cast-rolling area on microstructure of Al-8Si alloy cast-rolling plate

Al-8Si alloy cast-rolling strip billet was prepared by the continuous cast-rolling method,and the influences of different lengths for cast-rolling area on microstructure and central segregation for cast-rolling plate were studied by optical microscope(OM),scanning electron microscope(SEM)and energy dispersion spectrum analysis(EDS).Researches show that with the increasing of the length for cast-rolling area,the range of segregation increases first and then decreases.The increasing of length for cast-rolling area resultes in the increasing of the cooling strength for cast-rolling area,and the stronger cooling speed accelerates the solidification of molten metal to reduce the degree of central segregation.Furthermore,the morphologies of eutectic silicon on the surface and in the center of Al-8Si alloy in the same cast-rolling area are quite different.The eutectic silicon on the surface is distributed in a network,and the microscopic morphology is mostly fibrous,but a small part is petal-shaped.The morphology of eutectic silicon in the central layer is clustered along different orientations to form a middle line segregation.This is because when the cast-rolling billet is rolled,the upper and lower layers are in contact with the roll surface first,and the cooling speed of the central layer is slower than that of the upper and lower surfaces,so the central layer solidifys at last and the upper and lower surfaces have smaller grains than the center layer.