A Study On Near-rapidly Solidified Al-Zn-Mg-Cu Alloy

The Al-Zn-Mg-Cu ultra-high strength aluminum alloy possesses the advantages of low density,high specific strength,good corrosion resistance and superior processing performance and finds applicationsto broad fields ofaerospace products,high-speed EMU and other advanced manufacturing fields.The strength of Al-Zn-Mg-Cu alloys depends on the content of Zn and Mg in alloy.High contents of Zn and Mg are in favor of the formation of the strengthening phase Mg2 Zn and give rise to the increase of mechanical properties of the alloy.However,in the traditional casting process,the content of Zn usuallyremains no higher than 8 wt%in order to prevent the mechanical properties of the alloy from deteriorating.Under the condition of near-rapid solidification,the content of Zn can be increased to a higher level and the mechanical properties of the alloy can be further improved.In this work,the microstructures and mechanical properties of the high Zn-containing alloy prepared via near-raped solidification was studied.The purpose of this study is to optimize mechanical properties of the high Zn-containing Al-Zn-Mg-Cu alloysby optimizing the processes of homogenization treatment,solution treatment and agingtreatment.The effect of the contents of the main alloying elements Zn and Mgand the addition of trace Ce on microstructure and mechanicalproperties of the nearrapidly solidified Al-Zn-Mg-Cu alloy were investigated by means of X-Ray diffraction(XRD),differential scanning calorimeter(DSC),scanning electron microscope(SEM),energy dispersive spectroscopy(EDS)and other modern analysis methods.The results shows that with the increase of the content of Zn and Mg,the amount of dendritic and dendritic arm spacingdecreased,the grain boundary area increased and the grain structures was refined,which promoted the main alloying elements segregating towards grain boundary.However,high level of Zn caused the formation of a lot ofeutectic intermetallics which cut off the matrix.Trace Ce played a role of refining grain and purifying molten alloy.The addition of Ce decreased the dendritic arm spacing,increased grain boundary area,decreased the size of shrinkage and inclusions relatively,reduced the layer spacing of eutectic phase and refined the eutectic structure and the grain significantly.With the increased of the content of Zn and Mg,the amount of non-equilibrium eutectic phase increased gradually.During homogenization,the non-equilibrium eutectics dissolution into the matrix.Increasing the contents of Zn and Mg resulted in the increase of the yield strength and tensile strength and,however,the slightdecrease ofelongation of the alloy solidified under near-rapid cooling.The addition of trace Cedecreased the initial melting temperature of the eutectic intermetallics and refined the eutectic structure and the grain significantly.And the tensile strength and elongation of the alloys were greatly increased.