| In order to solve the problem of large weight of the fuselage,many scholars at home and abroad have focused on the research of the overall fuselage siding structure and its manufacturing technology.During the research period,many body siding structures were designed,among which the most Representative of the skin is a long welded structure and a bonded structure.Compared with these wall structures,the aluminum-lithium alloy has no residual amount of overall extruded wall structure,low dispersion rate,high quality reliability,anti-aging,high heat resistance and long service life.As a new type of aluminum-lithium alloy which is independent in China,X2A66 has lower density and higher elastic modulus.at the same time,it also has good formability(maximum tensile strength up to 510 MPa,elongation of more than8%,KIC up to 30 MPa1\2),high strength and high toughness,Corrosion resistance,good thermal stability,and other excellent properties,it is very suitable for the manufacture of aircraft overall siding structure.Since the extrusion process of the fuselage needs to be carried out under high temperature conditions,it is of great significance to analyze the influence of high temperature deformation on the microscopic deformation mechanism of the material to improve the forming properties of the material.In this thesis,the microstructure evolution and high temperature deformation mechanism of X2A66 Al-Li alloy during high temperature drawing are investigated.The X2A66 alloy was prepared by smelting and casting,and the obtained ingot was subjected to two-stage homogenization treatment at 400 ? / 12 h + 500 ? / 36 h,and a plate having a thickness of 3.0 mm was produced by a two-roll reversible rolling mill.Stretching to failure test(10-2 s-1,10-3 s-1)and strain rate test(5.75 × 10-5 s-1?2.49× 10-2 s-1)at 300 ?,350 ?,400 ? and 450 ?,and the microstructure was observed and analyzed by optical metallographic microscope and scanning electron microscope.The experimental data show that the elongation of X2A66 alloy is more than100% at 10-2 s-1,450 ? and 10-3 s-1,400 ? and 450 ?,the maximum elongation is130.51%.The deformation mechanism of the alloy changes with the change of temperature,and the second phase particles are enhanced to become dislocation climbing creep.The stress index n decreases with increasing temperature,from 12.75 to 3.92.Under the experimental conditions where the elongation exceeds 100%,the stress indices are n ? 3.48 and n ? 3.04,respectively.The creep activation energies were Q = 142.9 k J·mol-1 and Q = 131.9 k J·mol-1,respectively. |
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