Microstructural evolution of the non-dendrite A357 aluminum alloy billets heated by the multi-workstation rotating electromagnetic induction was analyzed including quantitative metallographic observation and theoretical model calculation. The results reveal that there exist two stages in the microsrtuctural evolution of the primary α-Al phase in the alloy billets during electromagnetic induction heating with 75kW. The first stage

with heating time from 0 to 303 seconds

eutectic structure is melted and grain is grown by emerging

meanwhile

the average diameter of grain is increased;the second stage

the primary α-Al phase is refined accompanying with spheroidization. The average grain diameters in the billets are 87.8 μm on the top

85μm in the middle and 84.9 μm at the bottom with shaping factors of 1.37

1.44 and 1.40

respectively. Growth of α-Al phase is characterized by the Ostwald growth mechanism. Based on the Ostwald ripening theory

the growth exponent of 2.2

2

.7 can be calculated. According to the calculated result

the average grain diameter in A356 aluminum alloy billets can be controlled to 66.3μm after electromagnetic induction heating.