Themicrostructuresaftercastingandextruding,themechanicalpropertiesandelectricalconductivityafterRRAtreatmentofconventionalDCcastingandlowfrequencyelectromagneticcasting(LFEC)7075aluminumalloywereinvestigated.TheresultsshowedthatfinergrainswhichdistributedmorehomogeneouslywasobtainedinLFECingotscomparedwiththoseconventionalDCingots.TheextrudedbarsofLFECalloykeptitsfinegrainfeaturesoforiginalas-caststructure.IntheRRAtreatment,withtheextensionofsecondagingtime,thetensilestrengthandhardnessofalloydecreased,buttheelectricalconductivityincreased.Meanwhile,asthesecondagingtemperatureraised,thephasechangerateinprecipitationalsoincreased.Underthesameconditions,extrudedbarsofLFECalloyhadbetterperformancethanthatofconventionalDCcastalloy.TheoptimumRRAheattreatmentprocesswas120℃/24h+180℃/30min+120℃/24h.TheLFECextrudedbarsacquiredtensilestrength676.64MPa,hardness198.18,andelectricalconductivity35.7%IACSrespectively,whichwerehigherthanthatintheT6temper,indicatingthatanotableRRAresponsetakesplaceinLFECextrudedbars,whosesecond-stepretrogressiontimewas30min,anditwassuitableformassproduction.
