The Specificities Of Semi-solid Squeeze Casting A319 Alloy In Heat Treatment

A319 alloys are widely used in aviation,aerospace,automobile,machinery and other industries for their excellent casting performance,mechanical properties,corrosion resistance and low cost.Semi-solid squeeze casting A319 alloy is attracting increasing attention for its superiority in microstructure and properties,compared with ordinary permanent mould gravity casting A319 alloy.In order to further improve A319 alloys' mechanical properties,heat treatment is applied.Effects of heat treatment on microstructure and mechanical properties of A319 alloys were studied by optical microscopy(OM),X-ray diffractometer,scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),transmission electron microscopy(TEM),Vickers hardness tester and electron-tensile tester.The specificities of semi-solid squeeze casting A319 alloy in heat treatment were investigated.A319 alloy consists of primary ?-Al phase,eutectic Si,?-Al2Cu phase,Q-Al5Cu2Mg8Si6 phase and Fe-containing phase(impurities).Attributing to the small segregation and high solidification rate,the morphology of Al2Cu phase in semi-solid squeeze casting A319 alloy is eutectiform,distributed in the boundary,and Q-Al5Cu2Mg8Si6 phase has two forms,eutectiform and platelet,distributed in the boundary.While,due to the severe segregation and low solidification rate,the morphology of Al2Cu phase in permanent mould gravity casting A319 alloy is block,distributed among the matrix and boundary,and Q-Al5Cu2Mg8Si6 phase is also compact block,distributed among the matrix and boundary.Solution treatment temperature for A319 alloy,which is affected by the melting temperature of Q phase,can be set to 505 ?.Affected by the morphology of Cu-containing phase,the time needed for dissolving Cu-containing phase in semi-solid squeeze casting A319 alloy is shorter than that for permanent mould gravity casting A319 alloy.505 ?×3h is available for the former alloy.Affected by the morphology of Si and Cu-containing phase,solution treatment process for the latter alloy could be set to 505 ? ×8h.The main process of precipitation in semi-solid squeeze casting A319 alloy is as follows:supersaturated solid solution?formation of G.P.I zones?formation of G.P.?zones?dissolution of G.P.Zones?formation of metastable phases(?' and Q')?formation of equilibrium phases(? and Q).Compared to the permanent mould gravity casting A319 alloy,the number of G.P.zones in semi-solid squeeze casting A319 alloy is more.The time needed for semi-solid squeeze casting A319 alloy to reach the aging peak is shorter.The optimum heat treatment process for semi-solid squeeze casting A319 alloy is 505 ? ×3h+175? ×80h(T6 heat treatment)?The tensile strength and elongation rate of semi-solid squeeze casting A319 alloy could reach 400.7Mpa and 3.0%respectively after T6 heat treatment.And they had an increase of 61.0%and 15.4%respectively,compared with as-cast alloy.