| The lightweight of automobiles is one of the development trend in automobile industry.Reducing the dead-weight of automobile can not only cut down the excessive consumption of fossil energy and relieve the air pollution,but also increase the speed of automobiles.In the automobiles industry,Al/Fe bimetallic composites have attracted an extensive attention from researchers who endeavor to explore some new applications of those materials in body structures of automobiles.Those materials have a perfect combination of the high strength,the good abrasive resistance,the nice vibration-resistance from Fe and the lightweight,the good thermal conductivity,the high toughness from Al.However,the solder oxidation of Al melt can weaken the wettability of Fe matrix in Al melt.Too thick or thin intermetallic phase layer can restrain the increasing of interfacial bonding strength of Al/Fe.Those disadvantages have constrained the extensive application of Al/Fe bimetallic composites in the body structure of automobiles.Shear property that behaves as the one of important criterions characterizing the interface bonding quality of Al/Fe is rarely reported on the theory and the technology.The interface morphology that is one of factors affecting shear property of Al/Fe composite interface is also seldom reported.In present works,we develop a new composite casting technique consisting of the surface pre-treatment of cast iron,the hot-dipping in Zn-0.2 wt.%Bi melt as well as the Al/Fe composite process.By the technique,not only a sound metallurgical bonding of Al/Fe but also the great improvement of shear property can be obtained.The improved shear property of Al/Fe composite interface is up to 32 MPa.In order to investigate effects of the new technique on the microstructure,the shear property of Al/Fe interface layer,we make a contrast analysis among the new composite technology,the hot-dipping in Al-7Si melt,the hot-dipping in pure Zn melt,the hot-dipping in Zn-2.2 wt.%Al melt.Results of shear testing present the shear property from the later three techniques:about 11 MPa,19 MPa,22 MPa.The contrast reveals that the higher shear strength obtained by the new technique is attributed to the formation of the concave-convex interface(CCI)morphology in Al/Fe bimetallic composites.The block-shaped Al-Fe phases,the thicker Al-Fe phase layer and the more needle-like Al-Fe phases all have a harmful effect on the shear property of Al/Fe interface layer.Nevertheless,the CCI morphology can enhance the shear property of Al/Fe bimetallic composites.We also investigate the effect of hot-dipping parameters on the microstructure and the shear property of Al/Fe composite interface.We find that Al-Fe intermetallic compounds(IMC)grow out from the interface between the graphite and the ferrite under the role of some hot-dipping parameters.With the increasing amount of Al-Fe IMC in the graphite-ferrite interface,the shear property of Al/Fe interface layer is weakened.Another discovery is that Bi element can promote the formation of Zn-rich regions in the graphite-ferrite interface,leading to the formation of Al-Fe IMC(Al-Fe intermetallic phases)in these Zn-rich regions.Through contrasting those results of shear testing,we find that the CCI morphology can benefit the increasing of shear performance.Therefore,it is necessary to make certain the formation process of Al/Fe CCI and the mechanism of CCI enhancing the shear property of Al/Fe composite interface.In order to further understand the formation process of the CCI,we make a model to account for the formation of CCI morphology.Besides,a mechanical model analyzing the stress state in Al/Fe composite interface is built for demonstrating the mechanism of CCI morphology increasing the shear property of Al/Fe composite interface. |
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