Electromagnetic Stirring On The Organization And Segregation Of The Aluminum Alloy Semi-solid Slurry

Semi-solid forming technology is a newly developed material processing technology, and there are many researches on the effects of electromagnetic stirring and the realated properties in recent years..In this study, the effects of the stirring intensity, stirring method and length of the interval time between normal-reverse stirring on the microstructure and segregation of primary a in Al-Cu alloy were investigated.The conclusion of the experiment which studied influences of the three factors talked above on the microstructure of primary a in Al-Cu alloy shows that a minimum change of the grain size under low stirring strength, and the size of primary a changed from former dendrites to equiaxed grains when the stirring strength raise up to a certain value. However, the grain size shows a minimum variation when the stirring strength reaches a critical value. At the same condition, the normal-reverse stirring has the best stirring effects among the three stirring methods which are normal stirring; pulse stirring and normal-reverse stirring. Because of the liquid flowing is most severely under normal-reverse stirring. And the effective time is longer under normal-reverse stirring than impulse stirring. For this reason, research on the influence of interval time of normal-reverse stirring on the microstructure of primary a was improved. It is pointed out that interval time have large impact on microstructure of primary a. The size of primary a decreases with prolonging interval time and it's because of the effective time increases the effective stirring time.The research on the macro structure of the primary Al-Cu alloy showed that under the electromagnetic stirring, the solute distributed more uniformly than the normal condition because the compel flowing make the solute in the liquidity more even. As the result from the start of the solidification to the end of the solidification the uniform solute concentration was more even. Furthermore, the primary a distributed more equally with the increasing stirring strength, that is to say, the degree of macro-segregation was greatly decreased. On the other hand, because of the different density between solid primary and liquid, the liquid move towards the center of the cast but the primary solid remove towards the margin of the cast. This phenomenon mainly occurred at the top of the cast. The reason is considered to be that the top of the cast is located at the part which is subject to the strong centrifugal force caused the whirling. The other contribution of the electromagnetic stirring was that it made the size of macrostructure more refined, and the grain size coarsens with the increasing stirring strength.