Determination of the critical fraction of solid during the solidification of a PM-cast aluminium alloy

OpenAlex · English

During the solidification of aluminium alloys, a flow of the interdendritic liquid through the mushy zone plays an important role in the feedability and shrinkage-driven porosity formation.Therefore, for almost all the studies about casting modelling, a good knowledge of the mushy-zone behaviour is necessary.In this study, the limit of the mushy-zone permeability for permanent-mould (PM)-cast aluminium alloys was investigated.A novel experimental technique was developed to quantify the value of the critical fraction of solid (CFS) at which the interdendritic feeding stops.Grain-refined and non-grain-refined aluminium alloys were used to evaluate the effect of the grain size on the CFS limit of both the non-grain-refined and fully grain-refined alloys.Three different initial mould temperatures were used to find if the mould temperature has any effect on the feeding of a casting.Alloys of varying solidification intervals were also used to determine the critical fraction of solid (CFS) for the feeding limit of solidifying castings.The results showed that the CFS values for solidifying aluminium alloys may vary from 34 % to 57 % depending on the casting conditions.The results also showed that for A356 aluminium-alloy castings the CFS value is not an alloy property, yet it significantly depends on the parameters such as the grain refinement and the modification of eutectic silicon.Keywords: critical fraction of solid, mushy-zone permeability, PM casting Med strjevanjem aluminijevih zlitin ima tok meddendritne taline skozi testasto podro~je pomembno vlogo pri napajanju in nastajanju poroznosti zaradi kr~enja.Zato je skoraj v vseh modelih ulitkov potrebno dobro poznanje vedenja testastega podro~ja.V tej {tudiji je bila iskana meja prepustnosti testastega podro~ja pri aluminijevih zlitinah, ulitih v stalne forme (PM).Razvita je bila nova eksperimentalna tehnika za oceno kriti~nega dele`a strjene faze (CFS), pri kateri se meddendritno napajanje ustavi.Uporabljene so bile aluminijeve zlitine z udrobnjenimi in neudrobnjenimi zrni za oceno vpliva velikosti zrn na mejno CFS pri obeh vrstah zlitin.Izmerjene so bile tri razli~ne temperature kokil, da bi ugotovili, ali temperatura kokile vpliva na napajanje ulitka.Uporabljene so bile tudi zlitine z razli~nim intervalom strjevanja, da bi ugotovili kriti~en dele`trdne faze (CFS), ki pomeni mejo napajanja pri strjevanju ulitkov.Rezultati so pokazali, da vrednosti CFS variirajo med 34 % in 57 %, odvisno od razmer pri ulivanju.Rezultati so tudi pokazali, da pri ulitkih iz aluminijeve zlitine A356 vrednost CFS ni odvisna samo od zlitine, temve~je zelo odvisna od parametrov, kot sta zmanj{anje zrn in modifikacija evtekti~nega silicija.