Study On Heterogeneous Interface Design,microstructure And Properties Of Steel/Aluminum Additive Composite Manufacturing

In order to realize the development requirements of lightweight and meet the requirements of industrial production for high performance of materials,the research of composites has become one of the key points at present.Steel/aluminum composite not only has the characteristics of light weight and strong corrosion resistance of aluminum alloy,but also has the advantages of high strength,good wear resistance and low cost of steel.However,due to the large differences in melting point and physicochemical properties between steel and aluminum,the wettability of molten aluminum alloy on the surface of solid steel matrix is poor,resulting in a large number of cracks at the steel/aluminum composite interface,which seriously affects the bonding effect of steel/aluminum interface.In view of the problems existing in the steel/aluminum composite casting,this topic improves the steel/aluminum interface bonding effect and improves the interface bonding strength by studying the hot-dip coating process on the steel surface,the composite casting process of the steel matrix with convex structure on the surface,the lattice structure design on the steel matrix surface,and the composite casting process of the steel matrix with lattice structure on the surface.The effects of different processes on the microstructure and phase composition of steel/aluminum interface were analyzed by metallographic microscope,scanning electron microscope and XRD.The effects of different processes on the mechanical properties of steel/aluminum interface were studied by measuring the microhardness and shear strength of steel/aluminum interface.The main research contents and results of this subject are as follows:(1)When the steel is hot-dipped in pure Al and Al-Si alloy,the thickness of intermetallic compound layer at the steel/aluminum interface gradually increases with the increase of hot-dip time.When steel is hot-dipped into pure Al,the intermetallic compounds at the steel/aluminum interface are Fe₂Al₅phase and Fe Al₃phase.The growth kinetic equation between the thickness of intermetallic compound layer and reaction time isx(28)1.04982?10^-6t^0.50661,and the reaction rate k=1.04982×10^-6.When steel is hot-dipped into Al-Si alloy,the intermetallic compound at the steel/aluminum interface consists of Fe₂Al₅phase and Al₈Fe₂Si,Al_4.5Fe Si,the growth kinetic equation of the thickness and reaction time of the intermetallic compound layer is x(28)3.2785?10^-7t^0.63548,and the reaction rate k=3.2785×10^-7,the existence of Si reduces the diffusion rate of Fe and Al atoms and inhibits the growth of the intermetallic compound layer.The best hot-dip Process of steel is hot-dip in Al-Si alloy for 10 minutes.(2)The steel matrix with bump structure on the surface is not hot-dipped,and there is an obvious gap at the steel/aluminum interface on the macro,and the interfacial shear strength is 9.6MPa.After hot-dipping in Al-Si alloy for 10 minutes,Fe₂Al₅phase,Al₈Fe₂Si and Al_4.5Fe Si phase are formed at the interface.The interfacial shear strength is 48.7MPa.The microhardness of the steel matrix is 245?270HV,the microhardness of the intermetallic compound layer is 535?600HV,and the microhardness of the aluminum matrix is about 70HV.(3)In order to further improve the shear strength of the steel/aluminum interface,the surface of the steel matrix was designed into a complex porous lattice structure.The effects of casting mode,porosity and pouring temperature on the microstructure and mechanical properties of the steel/aluminum interface were studied.(1)The steel matrix with 50%porosity lattice structure is compounded under gravity casting,there are large voids at the steel/aluminum interface,the bonding effect is poor,and the shear strength at the steel/aluminum interface is 6.27MPa.After compounding under squeeze casting,there are no macro defects such as cracks at the steel/aluminum interface.From the perspective of microstructure,there is a gap with a width of 8um at the steel/aluminum interface,the bonding effect is improved,and the shear strength at the steel/aluminum interface is 42.8MPa.(2)When the pouring temperature and extrusion pressure are the same,the gap at the interface decreases gradually with the increase of porosity.When the porosity is 70%,there is basically no gap at the interface and no metallurgical bonding occurs.When the porosity is 50%,60%and70%,the shear strength of steel/aluminum interface is 42.8MPa,56.9MPa and66.2MPa respectively.(3)After improving the lattice structure with porosity of 70%,when the pouring temperature of molten aluminum alloy is 730?,there is no gap and no metallurgical bonding at the steel/aluminum interface,and the interfacial shear strength is108.8MPa.When the pouring temperature of molten aluminum alloy is760?,Al_4.5Fe Si intermetallic compound with a thickness of 2um is formed at the steel/aluminum interface,the shear strength of steel/aluminum interface is 118.1MPa.