The structures in vacuum-assist high-pressure die casting(HPDC) AM60 B alloy were studied by using an optical microscope and a scanning electron microscope with an energy dispersive spectrometer.It was found that the HPDC under the vacuum could significantly change the morphology and distribution of the microstructure.For both conventional and vacuum-assist HPDC processes,the externally solidified crystals(ESCs) tended to aggregate in the center along the thickness direction of the castings.Besides,the aggregation was more pronounced,and the number of ESCs decreased,and the ESCs tended to become smaller and more globular,as the distance between the specimen location and runner increased.Compared with the conventional castings,the vacuum-assist HPDC can significantly reduce the size and amount of ESCs,and the ESCs tended to be more globular.For the distribution of ESCs along the thickness of the specimens,the aggregation tendency was more pronounced in vacuum-assist die castings than that in conventional castings.Besides,the distribution of ESCs at different locations was more converged in the vacuum-assist HPDC than that in the conventional HPDC.
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