Study On Semi-solid A390Alloy Prepared With Near-liquids Casting

The semi-solid A390alloy prepared by near-liquidus casting was studied in this paper.The evolution of solidified microstructure of A390alloy with processing parameters wasexplored. And the evolution of microstructure of the semi-solid alloy obtained bynear-liquidus casting was studied during remelting.The semi-solid A390alloy was prepared by near-liquidus casting, and the evolution ofsolidified microstructure with holding temperature and time was explored while the alloywas held around the liquidus temperature. The results show that: A390alloy was held withtemperature changing from695℃to620℃. While the holding temperature decreased from695℃to650℃, the α(Al) transformed gradually from dendrite to rosette and then intospherical shape. And the primary Si was gradually changed to be more refined and roundedparticle. The fine primary Si particle and nearly spherical α(Al) could be obtained withholding the alloy at635～650℃for40～55min. It was found that, with increasing coolingrate, the primary Si and α(Al) became finer.The rule of microstructure transformation of modified A390alloy was studied bycontrolling holding temperature and time. The results show that: Comparing withundermodified A390alloy, while the holding temperature decreased from740℃to650℃,the α(Al) in modified alloys can be changed from dendrite to rosette and then into grainystructure. But the transformation rule of the primary Si in modified alloys was differentfrom in undermodified alloys. Even the alloy was in high temperature, the primary Si wasmuch more refined and rounded. And with the reducing of temperature, the size of theprimary Si was much more refined. But changes in the amplitude became smaller. Whilethe alloy was holding at650℃, with the increasing of holding time, the evolution of theα(Al) in modified alloys was the same with in undermodified alloys. But the primary Siappeared the trend of coarsing.The evolution of microstructure of A390alloy was studied by controlling remeltingtemperature and time, while The semi-solid alloy billets obtained by near-liquidus castingwere remelted during the liquid-solid zone. The results show that: The globe rate of α(Al)increased with the increasing remelting temperature. And the roundness increased with theextension of the insulation time. Fine primary Si and non-dentritic α(Al) could be obtainedwith remelting the alloy at565℃～570℃for25min. The evolution of microstructure ofthe remelting alloy which was obtained during different solidification conditions was explored. The results show that: With the higher cooling rate, the microstructure of thecasting billets could be refined. And rosette structure could be acquired. It also speeded upand improved the spheroidization of solid particles.