| Al-Zn-Mg-Cu alloys are high strength and ductility and lightweight structural materials.It is widely used in load-bearing components of the aviation industry.Taking new-type Al-Zn-Mg-Cu alloy with high strength and ductility as the research object.the thermal compression test was carried out using Gleeble-3500 thermal simulator.The high-temperature rheological behavior of the alloy was studied and the constitutive equation and hot processing map of the alloy were established.Designed large deformation tests at sample level and sample level.Useing OM,SEM and other means to explore the dynamic recovery and dynamic recrystallization behavior of the alloy during high-temperature plastic deformation.The relationship between the mechanical properties and the structural characteristics of the alloy after deformation is revealed.The effect of the solid solution and artificial aging process on the structure and properties of the deformed sample was studied,and the law of strengthening and toughening of the alloy was obtained.Provide technical and theoretical guidance for the engineering application of this kind of high strength and toughness aluminum alloy.The main conclusions can be drawn:(1)The new Al-Zn-Mg-Cu alloy exhibits typical dynamic recovery characteristics during unidirectional compression.It has positive strain rate sensitivity and negative temperature sensitivity.The flow stress model expressed by the Z parameter is established,and the average activation energy of the alloy is 112.45 k J·mol-1.(2)Based on the dynamic material model,the hot working diagrams of the alloy with different strain levels are established.The strain has a great influence on the rheological instability zone and power dissipation value of the alloy.As the strain increases,the rheological instability zone gradually increases,and the safe processing zone gradually decreases;the power dissipation coefficient gradually increases.The structural analysis results of the instability area and the safe processing area in the hot working diagram show that the microstructure characteristics of the alloy in the rheological instability area are mainly local rheology and voids,while the microstructure characteristics in the safe processing area are dynamic recrystallization and dynamic reply.The suitable processing parameters of the alloy under the experimental conditions are determined:the temperature range is between 430??470?,and the strain rate range is between 0.01 s-1?0.2 s-1.(3)Through the cyclic squeeze test at the sample level,the process parameters matching the best performance are explored,and then the physical test at the sample level is carried out according to the best process parameters.In the sample-level pier extrusion test,it was found that direct use of lower temperature deformation has a strong ability to refine grains,but there are microscopic defects,resulting in poor mechanical properties,with a tensile strength of299MPa and an elongation of 12.4%.Directly adopt the method of high temperature deformation,the tensile strength is 320MPa,the elongation rate is 18%,and the material is ductility but not strength.The first deformation at high temperature and the second deformation at lowering temperature have a stronger effect on grain refinement,and can more effectively improve the performance of the material.The tensile strength reaches 332.5MPa,and the elongation reaches 15.5%,achieving a better balance of strength and ductility.Therefore,in the sample-level test,the billet was firstly opened at 470°C,and then the annular channel corner extrusion was carried out at 430°C.(4)The heat treatment test of the sample-level components is carried out to explore the influence of solid solution and artificial aging on the structure and properties of the alloy plastic deformation samples.To determine the optimal heat treatment process parameters for the angular extrusion of the annular channel:solution treatment(480?×1h)and aging treatment(120?×24h).Successfully prepared a high-strength aluminum alloy sample.The tensile strength of the sample from the body reached 630MPa and the elongation reached15.7%.The main reasons for this new Al-Zn-Mg-Cu alloy material to achieve better toughness is:After cooling the annular channel,the corner extrusion plastic deformation and the heat treatment process can greatly refine the crystal grains,so that the nano-level precipitates are uniformly dispersed and distributed.Compared with the homogenized state,the average grain size is reduced from 400?m to 132?m,the alloy elongation is increased from 4%to 15.7%,and the alloy strength is increased from 289MPa to 630MPa.It mainly includes three strengthening mechanisms:fine-grain strengthening,precipitation strengthening and dispersion strengthening. |
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