| The ultra-high strength 7000 series aluminum aloy has a major application background in key fields such as aerospace and weaponry.In this paper,through the microstructure analysis and performance testing of 6 kinds of 7000 series aluminum aloys designed,the effects of different Ti contents,different Zn/Mg ratios,different extrusion processes and different multi-stage solid solution systems on the microstructure and properties of aluminum aloy extruded materials were investigated.The main research contents and conclusions are as follows:(1)The effects of 0,0.34 wt.% and 0.81 wt.% Ti contents on the microstructure and properties of Al-9.9Zn-2.6Mg-0.91Cu-0.2Zr-xTi hot extruded aluminum aloy were investigated.At the same time,the effect of cold extrusion plastic deformation processing on the microstructure and properties of Al-9.7Zn-2.6Mg-0.89Cu-0.2Zr-0.81 Ti aluminum aloy was studied compared with hot extrusion processing.Studies have shown that under the conditions of 450 °C×2 h+460 °C×2 h+470°C×2 h solid solution and 120 °C×24 h aging treatment,the addition of Ti in the aloy can significantly refine the grains.With the increase of Ti content,the amount of undissolved phase gradually increased,the dislocation strengthening became higher and higher,the tensile strength at room temperature is basically unchanged and then decreased,the highest true stress at 250 °C high temperature compression is significantly increased and then decreased.And after the addition of Ti element,the intergranular corrosion resistance of the aloy is slightly improved,and the exfoliation corrosion resistance performance is slightly decreased.The optimum composition is Al-10.2Zn-2.59Mg-0.92Cu-0.184Zr-0.34 Ti,the tensile strength at room temperature is 738.5 MPa,the maximum true stress at 250 °C is 357.4 MPa,and the elongation after fracture is 7.5%.The recrystalization degree of the aloy in cold extrusion state is obviously higher than that in hot extrusion state,the grain size is finer,the undissolved phase is slightly reduced,the tensile strength and plasticity at room temperature are basically unchanged,the maximum stress in high temperature compression at 250? is slightly reduced,and the intergranular corrosion resistance and exfoliation corrosion resistance are improved.(2)The effects of three Zn/Mg ratios of 3.76,3.98 and 4.22 on the microstructure and properties of Al-xZn-2.6Mg-0.94Cu-0.2Zr-0.83 Ti cold extruded aluminum aloy were studied.The research shows that under the treatment of 450 ?×2 h+460 ?×2 h+470 ?×2 h solid solution and 120 ?×24 h aging,when the Zn/Mg ratio of the al oy increases from 3.76 to 4.22,the crystal grains tend to grow,the undissolved phase increases,the dislocations strengthening changes little,the tensile strength at room temperature and elongation after fracture gradually decrease,and the intergranular corrosion resistance and exfoliation corrosion resistance slightly decrease.The best composition is Al-9.74Zn-2.59mg-0.94Cu-0.195Zr-0.83Ti(corresponding to Zn/Mg ratio of 3.76),the tensile strength is 727.77 MPa,and the elongation after fracture is 5.1%.(3)The effects of S1(450 ?×2 h+460 ?×2 h+470 ?×2 h),S2(450 ?× 2 h+460 ?× 2 h+470 ?× 2 h+480 ?× 2 h)and S3(450 ?× 2 h+460 ?× 2 h+470 ?× 2 h+480 ?× 2 h+490 ?× 2 h)on the microstructure and properties of Al-9.74Zn-2.6Mg-0.94Cu-0.195Zr-0.83 Ti cold extruded aluminum aloy were studied.The results show that under the aging treatment of T6(120 ?×24 h),with the increase of the maximum temperature and the holding time of the multi-stage solid solution system,the degree of recrystalization of the aloy gradually increases and the grain size becomes larger.The amount of undissolved phase gradually decreased,the dislocation strengthening decreased slightly,and the tensile strength at room temperature increased first and then decreased,and the resistance to intergranular corrosion and anti-flaking corrosion improved.The optimum multi-stage solid solution system is 450 ?×2 h+460 ?×2 h+470 ?×2 h+480 ?×2 h(water quenching),at this time the tensile strength of the alloy reaches 740.84 MPa,and the elongation after fracture is 4.6%.In this paper,Ti element is innovatively added to 7000 series ultra-high strength aluminum aloy with high aloying degree,and cold extrusion is adopted to carry out plastic deformation processing on the aloy,and the laws between Ti content,cold extrusion processing and microstructure and properties of the aloy are summarized. |
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