Study On Composition Design,preparation Technology,microstructure And Properties Of 780MPa Strength,50mm Single End Quenching Depth Ultra-high Strength Aluminum Alloy

Ultra-strength aluminum alloys are eternal major research topics.7000 series aluminum alloys are widely used in aerospace and other fields due to their excellent performance.However,due to the large size and thickness of forging,the cooling rate between the surface and the core during the heat treatment process is inconsistent,making the strength of the surface and core of the alloy are different.Therefore,this kind of alloy needs not only high strength but also good hardenability.In this paper,five kinds of high strength and low quenching sensitivity aluminum alloys were designed on the basis of a large number of Al-Zn-Mg-Cu aluminum alloy components,heat treatment technology and previous melting experience.The effect of Zn/Mg and Cu/Mg on microstructure,performance and as cast hardenability of ultra high strength rolled aluminum alloy,effect of heat treatment process on microstructure and properties of ultra-strength extrusion material and the microstructure and properties and anisotropy of extrusion-50% hot pressing material were studied by microstructure and performance test.The following are the main research work and conclusions of this article:(1)The effect of three different Zn/Mg ratios on the microstructure and properties of Al-x Zn-2.8 Mg-1.21 Cu-0.194 Zr rolled aluminum alloy were studied.The specific content of Zn are 11.45 %,8.86 % and 10.66 % and the Zn/Mg ratios are 4.16,3.27,and 3.61 respectively.It is found that with the increase of Zn/Mg ratio,the strength of the alloy is obviously improved(from 611.85 MPa to 671.44MPa),and the intergranular corrosion resistance of the alloy is significantly improved(from 121.19 um decrease to 74.92 um).The sum of the atomic radius difference and the total volume difference of the alloy becomes smaller,and the hardenability of the alloy becomes better(the single end quenching depth is increased from 54 mm to 66 mm),but the corrosion resistance of the alloy becomes worse.Therefore,when the composition of alloy is Al-11.45 Zn-2.75 Mg-1.23Cu-0.199 Zr,the comprehensive properties of the alloy are optimal.(2)The effect of two different Cu/Mg ratios on the microstructure and properties of Al-10.5 Zn-2.94 Mg-x Cu-0.192 Zr rolled aluminum alloy were investigated.The specific content of Cu are 1.16 % and 2.06 % and the Cu/Mg ratios are 0.393(D3)and 0.7(D4)respectively.It is found that with the increase of Cu/Mg ratio,the strength,plasticity,and exfoliation corrosion resistance of the alloy are not much different,and the resistance to intergranular corrosion is significantly degraded(from 105.32 ?m to 161.41 ?m),The sum of the atomic radius difference and the total volume difference of the alloy becomes smaller and the hardenability of the alloy becomes better(the single end quenching depth is increased from 54 mm to64 mm).Therefore,when the composition of alloy is Al-10.66 Zn-2.95 Mg-1.16Cu-0.199 Zr,the comprehensive properties of the alloy are optimal.(3)Through the composition optimization design,medium frequency furnace melting,large extrusion ratio and multi-step solid solution and aging process,the super extruded aluminum alloy was designed(the theoretical component is: 10.7Zn-2.8 Mg-1.2 Cu-0.2Zr).It is found that the tensile strength of the solid solution process at 450 ?×2 h+460 ?×2 h+465 ?×2 h and aging process at 121 ?×24 h is787.12 MPa,but the plasticity of the alloy is poor,and the elongation is only 5.47%;the alloy has good comprehensive properties under the solution treatment process:460 °C × 2 h +470 °C × 2 h +480 °C × 2 h +490 °C × 2 h and aging process: 121 °C× 5 h+133 °C×16 h.Although the strength of the alloy is lost a part,the tensile strength of the alloy is 777.09 MPa,but the plasticity(elongation from 5.47 %increase to 7 %)and resistance to intergranular corrosion(the maximum intergranular corrosion depth decreases from 99.45 ?m to 75.85 ?m)has a certain increase.The single-end hardenability of the alloy is 52 mm,and the hardenability of the alloy is better.(4)The microstructure and properties of extrusion-50 % hot pressing aluminum alloy in three directions of L,T,and S were studied to investigate whether there is anisotropy.It can be concluded that the mechanical properties and corrosion resistance of the extruded-50% hot pressed aluminum alloy in L,T and S directions are obviously anisotropic in three directions.The alloy has the highest tensilestrength,hardness,and low electrical conductivity in the L direction,which are748.98 MPa,186.3 HV,and 31.43 % IACS respectively.The tensile strength of the alloy in the T and S directions is about 80 MPa lower than that in the L direction and the hardness and electrical conductivity are also different.The maximum intergranular corrosion depth in the three directions of L,T and S are 274.99?m,179.8?m and 228.87?m respectively.The exfoliation corrosion ranks are PC,PB and PB respectively and the maximum intergranular corrosion depth of the alloy in each direction is quite different.In addition,the exfoliation corrosion morphology of the alloy in different directions are also different.Therefore,in three directions of L,T and S,there is obvious anisotropy in the mechanical properties and anti-corrosion properties of extrusion-50 % hot-pressed aluminum alloy material.This article experimentally verifies the influence of the sum of the difference in the atomic radii and the sum of the volume difference on the hardenability,and the effective control of the alloy composition,the microstructure and the as cast hardenability is realized.The super strong aluminum alloy with 780 MPa and 50 mm with single end quenching depth has been prepared.