Vol.20 No.4 王德仁等：A-24%Si合金半固态等温搅拌时的微观组织 ·339· 高于577℃的先期搅拌就已经使初生硅较为光滑和密实，到577℃等温搅拌时，由于固相率不 再变化，强烈的电磁搅拌也只能使金属液剧烈流动并带动硅粒子相互碰撞摩擦.初生硅的相 互碰撞摩擦，使得硅粒子破碎和光滑圆整，同时也使得硅粒子相互粘结长大，这2种相反行为 在等温搅拌20mi时达到平衡，再延长搅拌时间，初生硅的形状将不再变化. 3结论 (1)从800℃冷却到577℃过程中不对金属熔体搅拌，只在577℃下开始等温搅拌，这种搅 拌工艺对超过一定尺寸的初生硅具有碎化作用，但初生硅的形状改变不大，随着搅拌时间的 延长，初生硅的形状有所圆整 (2)金属熔体在800℃下浇注后，立即开始搅拌，并在577℃下等温搅拌，这种搅拌工艺对 初生硅形状变化有明显的作用，使初生硅变为球团状，内部变得致密，但当搅拌时间超过20 min后，尺寸变化不大. (3)强烈的电磁搅拌可以使过共晶A124%Si合金组织中出现球状的先共晶α相. 参考文献 1周国桢.铸造有色合金及其熔炼.北京：国防工业出版社，1982.12 2 Femings M C.Behavior of Metal Alloys in the Semi-Solid State.Metall Trans,1991,22A:957 Microstructrural Characteristics of Semi-Solid State Al-24%Si Alloy during Isothermal Electromagnetic Stirring Wang Deren Mao Weimin Li Shusuo Zhong Xueyou Material Science and Engineering School,UST Beijing,Beijing 100083,China ABSTRACT Microstructure characteristics of Al-24%Si alloy was studied at the condition of isothermal electromagnetic stirring.Experiment was divided two groups: Stiring and no stirring during cooling course.Isothermal temperature is 577c with shearing time up to 40 minutes.Results discover that primary silicon crystal fragmentation and agglomeration occurs simultaneously in the course of stirring.The size of primary silicon phase tends to a constant.Spherical phase appears in the microstructure. KEY WORD electromagnetic stirring;hypereutectic Al-Si alloy;microstructure