The 3D Characterization Of Fe-rich Intermetallics And Its Effect On Microporosity In Aluminum-silicon Alloys

Fe-rich intermetallic ?-Fe,which is common intermetallic in cast aluminum alloys,is deleterious to mechanical properties of the alloys due to its platelet-like morphology and separation influence to matrix.It has been reported that they have important effect on the formation of pores.With the development of 3D X–Ray computed tomography,researches on the 3D characterization of microporosity was achieved,and the investigation on 3D characterization of Fe-rich intermetallics has been carried out by researchers abroad whereas the investigation has not been reported in domestic.In this study,the method for analyzing 3D morphology and characterization of Fe-rich intermetallic ?-Fe by 3D X–Ray CT was conducted.The effect of Fe content and cooling rate on 3D characterization of ?-Fe in Al-Si casting alloys and the effect of 3D characterization of ?-Fe on microporosity were also analyzed and discussed.In order to investigate the effect of alloy composition(Fe and Cu)and cooling rate on 3D characterization of ?-Fe in Al-Si casting alloys,the wedge-shaped castings of Al-6Si and A319 alloys with different Fe contents were prepared,and the cooling rates was acquired by JSCAST and the phase transformations were calculated by Thermo-Calc.A series of specimens from Al-6Si and A319 alloys wedge castings were prepared for inspection of high resolution 3D X-ray CT,and the 3D morphology of intermetallics and micropores were reconstructed.The effects of Fe content and cooling rate on volume parameter,3D morphology and distribution of ?-Fe were investigated,and the effect of 3D characterization of ?-Fe on microporosity was also analyzed.The volume fraction of ?-Fe and the volume of the largest ?-Fe increased when increasing Fe content.The inter-connection of ?-Fe was found and the largest ?-Fe was windingformed by impingement of ?-Fe intermetallics at low Fe content;the largest ?-Fe shows a network of platelets,formed by the impingement and branching of ?-Fe intermetallics.When decreasing cooling rate,the volume fraction of ?-Fe increased and nucleation of ?-Fe decreased resulting in a very large network of ?-Fe platelets.The shrinkage pores with complex shape were usually observed in the Al-6Si alloys.It was found that the coarse binary ?-Fe can act as nucleation substrate of micropores and promote the growth of micropores.The 3D morphology and characterization of intermetallics(?-Fe and Al2Cu)in the A319 alloys with different Fe contents were analyzed and the effect of Fe-rich phase on Al2 Cu and microporosity was investigated.When Fe contents increased from 0.35wt%,the volume of intermetallics and the largest intermetalllics in the specimens increased while the intermetallic amounts decreased due to the formation of platelet-network among binary eutectic ?-Fe,which helps the nucleation and growth of Al2 Cu.Since the A319 alloys are with large solidification temperature range and mushy zone,the shrinkage pores were dominant in the alloys,and showed a more complex shape.The porosity content increased with the increased Fe content.