连续降温电磁搅拌对A356铝合金半固态组织的影响

Effect of continuous cooling electromagnetic stirring on semi-solid microstructure of A356 aluminum alloy

采用连续降温电磁搅拌法制备纯净的A356铝合金半固态浆料,通过显微组织观察和形状因子统计,研究了电磁搅拌频率、电磁搅拌温度区间和熔体降温速率对A356铝合金半固态浆料初生相形貌和尺寸的影响。研究结果表明:当搅拌条件为600℃炉膛预热、搅拌频率为30 Hz、搅拌温度区间为640℃~600℃时,半固态浆料初生相大部分为球形或椭球形;在初生相形成初期。更慢的降温速率有助于形成球形或椭球形的初生相。主要机制是更小的过冷度不足以使晶核发生快速的等轴生长或合并,但是大过冷度易于晶核合并生长且长大,从而形成蔷薇状或树突初生相。

The pure semi-solid slurry of A356 aluminum alloy was prepared with the method of continuous cooling electromagnetic stirring.The microstructure observation and shape factor statistics were used to study its primary phase morphology and size with different electromagnetic stirring frequencies,electromagnetic stirring temperature ranges and melt cooling rates.The results show that when furnace preheating temperature,stirring frequency and temperature range are 600℃,30 Hz and 640℃-600℃,respectively,the primary phases of semi-solid slurry are mostly spherical or ellipsoidal.In the early stage of primary phase formation,slower cooling rate is helpful to form spherical or ellipsoidal primary phase.The main mechanism is that smaller supercooling degree is not enough to cause rapid isoaxial growth or merger of crystals,but larger supercooling degree is easy to make crystals merge and grow,thus forming rose-like or dendritic primary phase.