Study On Thermal Deformation Characteristics And Application Of The Al-12Zn-2.4Mg-1.2Cu Ultra High Strength Aluminum Alloy

Ultra high strength aluminum with a high specific strength and stiffness, durable and economical, easy processing, good corrosion resistance and high toughness, etc., has become one of the preferred structural materials in aerospace, weapons, transportation and other industries.Research on the deformation behavior of self-developed ultra high strength aluminum alloy(Al-12Zn-2.4Mg-1.2Cu-0.3Zr-0.05Ni) has been carried out by thermal simulation test.The effect of different process parameters on the mechanical properties also has been Researched. Taking double convex disc-shaped part as an application target member, meanwhile, considering requirements of the high performance and its uniformity and characteristics of the stress sensitivity, state parameters(?’and?) and process parameter( ?W?) are proposed as uniform evaluation indexes to design the forming solutions and research on the forming uniformity.A combined optimization methods of gray related theory and orthogonal experiment is used for process parameters optimization and design for target part by numerical simulation technology. Finally, basing on the forming test results, performance homogeneity of the target component is studied by statistical methods.Hot deformation characteristics are carried out through the isothermal compression test. According to the proccesing maps of different true strain, the optimum deformation parameters are obtained. Based on the classic Arrhenius model, a new model is established considering strain compensation on the material constants and modified Z parameter by index. Compared with the classical model, prediction accuracy of the new model is improved 24.88%.Based on the flow curve and work hardening rate theory, the critical stress and strain conditions models of dynamic recrystallization are established. The characterization of recrystallization microstructure are obsered using metallurgical testing technology. The results showed that the average recrystallized grain size of the alloy increases with increasing temperature and reducing the strain rate. The microstructure model of the alloy is also be obtained by quantitative metallographic analysis and morphological image processing technology. The model is used for subsequent numerical simulation research.Based on the extrusion ratio test, the response results of different deformation parameters show that deformation temperature and extrusion ratio has a more significant effect on the mechanical properties of the alloy. Compared to the initial extruded bar(tensile strength 700-720MPa), the tensile strength of the secondary deformation increases by 7.9%-15.6%.In this paper,State parameters(?’and?) and Process parameter( ?W?) are used to design the forming solutions and evaluate the the forming uniformity, congsidering requirements of high service performance and its uniformity and characteristics of stress sensitivity.A combined optimization methods of gray related theory and orthogonal experiment is used for process parameters optimization and design for the first time. The grey relational grade of the deformation parameters, the stress and strain state and the energy distribution of the results of the energy distribution are studied. The correlation integration of multiple evaluation indexes is realized. The problem of forming process parameters optimization design in multi evaluation index can not be solved by the orthogonal test method. Multi pass isothermal forming process parameters are obtained. At the same time,the influence of different factors of those parameters on the forming uniformity is also acquiredFinally, the forming test, microstructure and performance test and characterization of the target are carried out. The results show that the multi pass isothermal forming(case2) technique is reasonable and feasible. The average tensile strength of the case2 scheme is higher than that of the 730 MPa, and the average elongation is greater than 5%, at room temperature. There is no significant differences in the sampling direction(P-value=0.168806) of the case2 forming part, which effectively ensures the consistency of the mechanical properties of the components. There is significant differences in the sampling direction(P-value= 0.780749) of the case1. The components with good mechanical properties are prepared by using the case2 and the optimized design parameters, which laid the foundation for the uniform forming and engineering application of the alloy.