| The ultra-high strength heat-resistant 7000 series aluminum alloy has a significant application background in key fields such as aerospace and weaponry.In this paper,the effects of Ti content,hot/cold extrusion,Zn/Mg ratio and multi-stage strengthening solid solution on the microstructure and properties of 7000 series aluminum alloy extruded material with Mg content of 2.4wt.% were studied.The main research work and conclusions are as follows:(1)The effects of Ti content(0,0.23 wt.% and 0.78 wt.%)and hot/cold extrusion on the microstructure and properties of Al-8.54Zn-2.4Mg-0.84Cu-0.2Zr-xTi aluminum alloy were studied.The results show that for 7000 series aluminum alloy hot extruded materials which have been treated by 450℃×2 h+460℃×2 h+470℃×2 h(water quenching)and 120℃×24 h aging treatment,after the addition of 0.23 wt.%Ti element,the internal grain of the alloy is refined,and the dislocation strengthening is improved.When the Ti element is added too much,the undissolved phase in the alloy increases.With the increase of Ti content,the tensile strength of the alloy increases first and then decreases,the resistance to intergranular corrosion increases first and then decreases,and the exfoliation corrosion resistance decreases.When the Ti content is 0.23 wt.%,the alloy has the best mechanical properties.When the Ti content is 0.23 wt.%,the alloy has the best mechanical properties.Compared with the Ti content of 0,the tensile strength of the alloy at room temperature is increased by38.97 MPa,reaching 725.49 MPa,and the elongation is 7.35%.When the Ti content is increased from 0 to 0.23 wt.%,the thermal compression peak stress of the alloy at250℃ is increased by 45%,and the stress reaches 320.41 MPa.For Al-8.54Zn-2.4Mg-0.84Cu-0.2Zr aluminum alloy,after cold extrusion instead of hot extrusion,the internal grain of the alloy is refined and the dislocation strengthening is improved.The tensile strength at room temperature is increased by 30.46 MPa and the strength is 716.98 MPa.The resistance to intergranular corrosion is improved,the exfoliation corrosion resistance slightly improved,and the thermal compression peak stress issimilar at 250℃.(2)The effects of three different Zn/Mg ratios(3.46,3.84 and 4.04)on the microstructure and properties of Al-xZn-2.4Mg-0.84Cu-0.2Zr-0.25 Ti aluminum alloy cold extrusions were studied.The results show that for 7000 series aluminum alloy cold extruded materials which have been treated by 450℃×2 h+460℃×2 h+470℃×2 h(water quenching)and 120℃×24 h aging treatment,when the Zn/Mg ratio increases from 3.46 to 4.04,the grain size of the alloy does not change much,the undissolved phase increases,the dislocation strengthening increases first and then decreases.when the Zn/Mg ratio increases from 3.46 to 4.04,the conductivity decreases,the tensile strength at room temperature increases first and then decreases.With the increase of Zn/Mg ratio,the resistance to intergranular corrosion first decreases slightly and then decreases,and the exfoliation corrosion resistance decreases.The optimum composition of the alloy is Al-9.29Zn-2.42Mg-0.83Cu-0.193Zr-0.24Ti(Zn/Mg ratio is 3.84).The tensile strength of the alloy of this component is 709.79 MPa,and the elongation after fracture is 9%.(3)The effects of three solid solution processes(G1:450℃×2 h+460℃×2 h+470℃×2 h;G2:450℃×2 h+460℃×2 h+470℃×2 h+480℃×2 h;G3:450℃×2 h+460℃×2 h+470℃×2 h+480℃×2 h+490℃×2 h)on the microstructure and properties of Al-9.91Zn-2.45Mg-0.85Cu-0.198Zr-0.27 Ti aluminum alloy cold extrusions were studied.The aging process was: 120°C×24 h.The results show that as the solution temperature increases and the time prolongs,the grain size of the alloy first increases and then increases,the undissolved phase decreases,the dislocation strengthening decreases.With the increase of solution temperature and time,the electrical conductivity increases,the room temperature tensile strength first increases and then decreases,and the resistance to intergranular corrosion and the exfoliation corrosion resistance is improved.The best solution process of the alloy is G2 solid solution process.After G2 solution treatment,the room temperature tensile strength reaches704.61 MPa,the elongation after fracture is 4.67%,The maximum intergranular corrosion depth is 116.90 μm,and the he exfoliation corrosion grade is EA grade.In this paper,Ti element is added to the 7000 series aluminum alloy,whichgreatly improves the heat resistance of the alloy.On the other hand,cold extrusion is used instead of hot extrusion to increase the room temperature tensile strength of the alloy without reducing the heat resistance of the alloy. |
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