| With the rapid development of the aerospace industry,people have put forward higher requirements for the comprehensive performance of ultra-high strength Al-Zn-Mg-Cu alloy.Scholars at home and abroad are also working to optimize the alloy composition and develop some new heat treatment.At present,it is a common method to add Zr,Sc and other trace elements to the Al-Zn-Mg-Cu-based aluminum alloy to improve its comprehensive performance.However,the optimal Cu content in the Al-Zn-Mg-Cu alloys with Zr and Sc and the effect of heat treatment on the microstructure and mechanical properties of the Cu content optimized alloy are the current research hotspots.In this paper,the microstructure and mechanical properties of Al-9.3Zn-2.52Mg(0.98?2.49)Cu-0.15Zr-0.078Sc alloy was characterized and analyzed by metallographic microscope,scanning electron microscope(SEM),transmission electron microscope(TEM),XRD diffractometer and tensile test.The influence of Cu content on the microstructure and properties of the alloy sheet was systematically studied and the Cu content range in the Al9.3Zn-2.52Mg-(0.98?2.49)Cu-0.15Zr-0.078Sc alloy was optimized.Furthermore,the effect of hot rolling deformation before homogenization on the microstructure and mechanical properties of Al-9.4Zn-2.59Mg-1.82Cu-0.16Zr-0.07Sc alloy sheet was further studied to reveal the influence of pre-deformation on the shape,size,quantity and distribution of micron-sized crystal phase particles in high-strength aluminum alloy sheet,and finally optimize the preparation process of the best short streamline of Al-9.4Zn-2.59Mg-1.82Cu-0.16Zr-0.07Sc alloy sheet The parameters provide basic data for the production of new ultra-high-strength aluminum alloys with good plasticity,toughness,fatigue properties and corrosion resistance.The main conclusions are as follows:(1)The type of T(AlZnMgCu)and Al7Cu2Fe excess crystal phase particles are approximately the same in hot-rolled Al-9.3Zn-2.52Mg-(0.98-2.49)Cu-0.15Zr-0.078Sc alloy sheets after solution quenching and then aging treatment.The disperse phase particles and the precipitated phase particles in alloy sheets are roughly the same in type,size and distribution.The dispersed phase particles are tens of nanometers of L12 structure Al3Zr and Al3(Zr,Sc)particles,and the matrix precipitated phase is ?' with a diameter of 5?10 nm.The grain boundary precipitated phase is ?,and the size is about 10 nm.However,the amount of excess crystalline phase particles and matrix precipitate phase ?' increases with increasing Cu content.(2)The grain size of hot-rolled Al-9.3Zn-2.52Mg-(0.98?2.49)Cu-0.15Zr-0.078Sc alloy sheets after solution quenching and then aging treatment is fibrous,however,the recrystallized volume fraction of the alloy sheet is increased from about 6%to more than 20%with increasing Cu content.(3)The strength of hot-rolled Al-9.3Zn-2.52Mg-(0.98?2.49)Cu-0.15Zr-0.078Sc alloy sheet after solution quenching and then aging treatment increases first and then decreases with the increase of Cu content,and the elongation first remains unchanged and then decreases significantly.When the Cu content is between 1.58%and 1.94%,the sheet has the best comprehensive performance,the tensile strength is about 670 MPa,the yield strength is about 650 MPa,and the elongation is over 11%.(4)The optimum Cu content of Al-9.3Zn-2.52Mg-0.15Zr-0.078Sc alloy was optimized to be 1.58%?1.94%.The corresponding short process was the 300?×12 h pretreatment.The yield strength,tensile strength and elongation of the alloy sheet after aging at 465?×1 h and then aged at 120?×24 h were 655 MPa,664 MPa and 11.5%,respectively.(5)Hot rolling before homogenization can promote the dissolution of the micron-sized alloy phase in the Al-9.4Zn-2.59Mg-1.82Cu-0.16Zr-0.07Sc alloy during the homogenization process.The soluble crystalline phase in the alloy ingot can be completely dissolved into the matrix after homogenization at 465? for 12 h when the hot rolling deformation is less than 73%;However,when the rolling deformation exceeds 73%,the crystalline phase is completely dissolved back into the matrix at 465? for 6 h.(6)The size of the excess crystal phase in the matrix of the Al-9.4Zn-2.59Mg-1.82Cu0.16Zr-0.07Sc alloy sheet solution quenching and then aging treatment becomes smaller,the quantity is reduced,the distribution is more uniform,the yield strength and tensile strength of the sheet are gradually increased,and the elongation of the alloy sheet remains substantially unchanged with the increase of pre-deformation when the homogenization treatment is 465?×2 h;When the homogenization time at 465? are 6 h,12 h,and 24 h,the amount of excess crystal grain in the Al-9.4Zn-2.59Mg-1.82Cu-0.16Zr-0.07Sc alloy sheet decreases first and then increases,the quantity is reduced first and almost unchanged,the distribution tends to be uniform,and the yield strength and tensile strength of the sheet show a trend of increasing first and then decreasing with the increase of pre-deformation.When pre-deformation before the homogenization treatment reaches 73%,the excess crystal phase particles have the smallest size and the smallest amount,and the yield strength and tensile strength of the alloy sheet are maximized,however,the strength is lower than the alloy sheet homogenizing at 465? for 2 h with more than 73%pre-deformation.(7)The optimal short streamline preparation process for optimizing Al-9.3Zn-2.52Mg1.82Cu-0.15Zr-0.078Sc alloy sheet is"DC ingot?300?×12 h pretreatment?pre-deformation exceeding 73%?465?×2 h homogenization?hot rolling?465?×1 h solution?120?×24 h aging",the yield strength and tensile strength exceed 658 MPa and 670 MPa,the elongation exceeds 11.4%,respectively. |
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