| High strength and heat resistance 7000 series aluminum alloy have important developing background in aerospace,military,automobile,ship and other industries.This paper studies the effects of Ti alloying,hot/cold extrusion,Zn/Mg ratio and multi-step solution on the structure and properties of high strength 7000 series aluminium alloys with Mg content of about 2.1wt%.The main research contents and conclusions of this paper are as follows:(1)The effects of Ti content(0,0.38,0.85wt%)and hot/cold extrusion on the structue and properties of Al-9.5Zn-2.1Mg-1.0Cu-0.2Zr-xTi extruded alloy strengthened by solution(450℃×2h+460℃×2h+470℃×2h,water quenching)and aging(121 ~oC×24)were studied.The results show that with the increase of Ti content,the grain size of the alloy decree-ses,dislocation strengthening increases,tensile strength and elongation after fracture incre-ases.The intergranular corrosion resistance,exfoliation corrosion resistance and 250 ~oC compressive strength are improved.Among them,Al-9.1Zn-1.95Mg-1.14Cu-0.2Zr-0.85Ti has the best comprehensive properties,with tensile strength reaching 724.6MPa,elongation reaching 13%,maximum intergranular corrosion depth 116.45um,peeling corrosion rating EA,250 ~oC compressive strength 211.5MPa,which is 98.2MPa higher than that of Al-alloy which Ti content is 0.Compared with hot extruded alloys,cold extruded alloys have significantly finer grains,more equiaxed grains,higher dislocation strength,higher tensile strength and elongation after fracture,and no significant changes in intergranular corrosion resistance,spalling corrosion resistance and heat resistance.The tensile strength of cold extruded Al-9.5Zn-2.0Mg-1.15Cu-0.19Zr-0.38Ti aluminium alloy increased by 35.3MPa,735.4MPa,and the elongation increased by 1.3%and 12.3%after fracture compared with that of hot extruded Al-9.5Zn-2.0Mg-1.15Cu-0.19Zr-0.38Ti aluminium alloy.(2)The effects of Zn/Mg ratios(4.75,3.86),(4.66,5.12),(4.66,5.12)and Ti content(0.38,0.85wt%),(4.66,5.12)and Ti content(0.38,0.85wtwt%)%on the microstructure and properties of solid solution(450℃×2h+460℃×2h+470℃×2h,water quenched)and again(121 ~oC×24)strengthened Al-xZn-2.1Mg-1.0Cu-0.2Zr-0.5Ti and Al-xZn-2.1Mg-1.0Cu-0.2Zr-1T were studied.The results show that with the increase of Zn/Mg ratio,grain refinement,dislocation strengthening,tensile strength and elongation after fracture are improved,and intergranular corrosion resistance and spalling corrosion resistance are improved.Among them,Al-9.5Zn-2.0Mg-1.14Cu-0.19Zr-0.38Ti and Al-10.5Zn-2.05Mg-1.02Cu-0.2Zr-0.923Ti have the best comprehensive properties,the tensile strength reaches 735.4MPa,690.4MPa,the elongation after breaking is 12.3%,9.6%,the maximum intergranular corrosion depth is 132.36um,103.36um,and the peeling corrosion rating is EA-,EA.(3)The effects of multi-stage solution(450℃×2h+460℃×2h+470℃×2h,water quenc-hing;450℃×2h+460℃×2h+470℃×2h+480℃×2h,water quenching;450℃×2h+460℃×2h+470℃×2h+480℃×2h+490℃×2h,water quenching)on the structure and properties of Al-10.5Zn-2.05Mg-1.02Cu-0.2Zr-0.923Ti cold extruded aluminium alloy were studied.The results show that with the increase of solution series,the grain size decreases first and then increases,the tensile strength and elongation increase first and then decrease,and the intergranular corrosion resistance and exfoliation corrosion resistance increase first and then decrease.When multi-stage solution(450℃×2h+460℃×2h+470℃×2h+480℃×2h,water quenching)is used,the properties of aluminum alloy are the best.The tensile strength of the alloy is 711.159 MPa,the elongation after fracture is 13%,the maximum intergranular corrosion depth is 88.72 um,and the scaling of spalling corrosion is EA+.In summary,this study finds that Ti alloying can improve the strength,plasticity,corrosion resistance and heat resistance of 7000 series aluminium alloys,cold extrusion instead of hot extrusion can improve the strength and plasticity of the alloys,and maintain the original corrosion resistance and heat resistance;the increase of Zn/Mg ratio can enhance the strength,plasticity and corrosion resistance of 7000 series aluminium alloys with Mg content of about2.1wt%;Solution process refines alloy grain and improves strength,plasticity and corrosion resistance. |
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