| 2A12 alloy is a typical Al-Cu-Mg hard A1 alloy with high specific strength and specific stiffness,good corrosion resistance and favorable fracture toughness and fatigue resistance.It is one of the most widely used structural materials in the aerospace industry.Currently,among 2A12 products,2A12 plate and strip has attracted more and more attention but has low performance and low yield restricted to technology and production level.These are engineering technical problems we are facing and urgently need to solve.However,the current research on technology and theoretical basis of 2A12 plate and strip are obviously insufficient.The microstructure of 2A12 Al alloy is complex,besides the matrix,containing a range of intermetallic(IM)particles.During the subsequent deformation and heat treatment,a series of complex changes of IM particles also occur,which affects the comprehensive properties of the alloy.However,there are few reports on the study of IM particles in 2A12 Al alloy,and the composition and classification of IM particles are still controversial.2A12 Al alloy is a typical heat-treatable A1 alloy,and heat treatment is an important means to change its structure,improve its performance and give full play to its material potential.Natural aged 2A12 Al alloy sheet is widely applied,but when application temperature or performance requirements are high,the artificial aging state should be adopted.Sometimes,in order to improve the properties of Al alloy,a certain degree of permanent deformation is needed before aging.The microstructure evolution of Al alloy during aging treatment is complex.Although there are many studies on aging precipitation behavior of Al-Cu-Mg alloy at present,the microstructure evolution of 2A12 A1 alloy under different heat treatment states still does not get enough attention.Therefore,it has important theoretical significance and application value to study the microstructure characteristics and clarify the relationship between heat treatment parameters and products properties of 2A12 Al alloy sheet.In order to explore the heat treatment process systems of 2A12 plate and strip,in this paper,cold rolled 2A12 Al alloy alclad sheet is taken as the research object,and a series of solution and aging heat treatment experiments were carried out.Combined with various test methods and characterization means,the microstructure and mechanical properties of cold rolled 2A12 Al alloy sheet were studied.The main research contents and conclusions are shown as follow:(1)The microstructure of cold rolled state 2A12 Al alloy sheet was studied,and the type,size,and distribution of constituent phases in the alloy were determined.A series of solution experiments were carried out at different temperature and time.The influence of different solution parameters on the size,distribution,and volume fraction of the second phases was studied by characterizing the microstructure of the alloy.The behavior of recrystallization and grain growth during solution treatment was revealed,and the factors affecting recrystallization and grain growth were explored.The morphologies of Al clad under different solution conditions were analyzed,and the reasonable solution temperature and time range were determined.The influence of solution parameters on the mechanical properties of 2A12 Al alloy sheet was studied by means of mechanical test,and the complex influence of overburning on the microstructure and properties of 2A12 Al alloy sheet was revealed.(2)A series of solution and aging treatment experiments were carried out for 2A12 Al alloy sheet in four states:T42.,T351.,T62,and T851,and the effects of aging temperature,aging time,and pre-deformation on mechanical properties of the alloy were studied.The fracture surfaces were analyzed by SEM,and the fracture characteristics of different state alloy and the main factors affecting alloy fracture toughness were revealed.The microstructure evolution of 2A12 Al alloy sheet during different artificial aging stages was studied by TEM,and the strengthening phase precipitation sequence for 2A12 Al alloy sheet was proposed.The differences in mechanical properties of 2A12 Al alloy under different heat treatment states were compared,and the results provide theoretical guidance for determining the application range of 2A12 Al alloy sheet in different states.(3)The Box-Behnken experimental design method was used to design 29 groups of solution and aging treatment experiments,and the response surface model of tensile strength,yield strength,and elongation were obtained by second-order response surface equation regression analysis.The ANOVA shows that the response surface models are of good significance.According to the response surface models,the response surfaces were plotted by using Design-Expert software,and the influences of solution and aging treatment process parameters on the mechanical properties of the alloy were deeply analyzed.Based on particle swarm optimization(PSO)and response surface model,single-objective and multi-objective optimization was carried out for the solution and aging treatment process parameters,and good optimization results were obtained. |
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