Study On The Regulation Of Residual Stress Cryogenic Treatment For The Deformation Of 2A12 Aluminum Alloy Thin-walled Cylinder Parts

Thin-walled cylinders are widely used as core components in cutting-edge products such as aerospace applications,and their machining accuracy and performance significantly impact the safety,effectiveness,and reliability of equipment operating under extreme conditions like high temperatures,high energy densities,and high pressures.However,during the machining of thin-walled cylinders,they are susceptible to the combined effects of cutting forces,cutting heat,and other factors,making it challenging to ensure processing quality and accuracy.One of the main sources of machining deformation is the release and redistribution of quenching residual stress.Based on this,focusing on the deformation issues encountered during the machining of thin-walled aluminum alloy 2A12 cylinders,this thesis takes the manufacturing process as the main thread and aims to improve the dimensional stability of aluminum alloy thin-walled cylinders.Adopting cryogenic treatment technology,the study manipulated both the initial residual stress generated during the heat treatment of aluminum alloy blanks and the machining residual stress introduced during rough machining,effectively controlling the deformation of thin-walled cylinders.Through microscopic analysis,this thesis reveals the mechanism by which cryogenic treatment affects the residual stress of aluminum alloy 2A12,providing valuable insights for improving the machining deformation of thin-walled cylinders.The main research contents and conclusions are as follows:(1)A finite element model was established to simulate the process of reducing initial residual stress in 2A12 aluminum alloy through cryogenic treatment.The study focused on examining the effectiveness of cryogenic treatment and aging processes in mitigating initial residual stress.Utilizing elastoplastic finite element theory,numerical simulations were conducted to analyze the evolution of residual stress during key processes such as heat treatment,cryogenic treatment,and aging treatment of aluminum alloy blanks.Compared to the residual stress on the surface of quenched samples,the residual stress after the introduction of cryogenic aging treatment decreased by approximately 69%.Validation experiments for cryogenic treatment were also conducted,and the results indicated that the adoption of cryogenic aging treatment can effectively reduce the initial residual stress in aluminum alloy.(2)With the goal of minimizing the initial residual stress on the surface of aluminum alloy thick plates,the optimal cryogenic treatment process parameters were obtained through range analysis:-196℃(cryogenic temperature),2h(cryogenic time),2 times(number of cryogenic treatments),and 3℃·min-1(cooling rate).The residual stress of aluminum alloy thick plate samples treated with the optimized cryogenic process was approximately 93% lower than that of untreated samples.Microstructural changes in the samples were observed using SEM,XRD,and TEM.When the aluminum alloy material is subjected to thermal stress,dislocation pile-ups within the material move along the slip plane and undergo dislocation annihilation,reducing the dislocation density within the material.This decrease in dislocation density reduces lattice distortions within the material,thereby releasing residual stress.This is the microscopic mechanism behind the reduction of residual stress in the samples.(3)The study investigated the impact of cryogenic treatment on the residual stress and dimensional stability of 2A12 aluminum alloy C-rings.Aiming for lower residual stress,good dimensional stability,and mechanical properties in the samples,the cryogenic treatment process was optimized using grey relational analysis.The optimized parameters were: cryogenic temperature of-196℃,cryogenic time of 2 hours,2 cycles of cryogenic treatment,and a cooling rate of 3℃ per minute.Analysis of variance revealed that the cryogenic temperature had the highest contribution to the overall performance of the aluminum alloy C-ring samples.Through cryogenic treatment experiments,it was found that samples undergoing cryogenic aging treatment exhibited a 74% reduction in machining deformation compared to those without such treatment.This indicates that reducing initial residual stress can enhance the dimensional stability of the samples.Additionally,compared to aluminum alloy samples that underwent natural aging after solution treatment,the tensile strength and yield strength of the aluminum alloy samples after cryogenic aging treatment increased by 28% and 17%,respectively.This demonstrates that the cryogenic aging treatment process significantly improves the strength of aluminum alloy samples.(4)To address the issue of deformation in the machining process of 2A12 aluminum alloy thin-walled tubular parts,a manufacturing process has been studied to reduce the deformation.A three-dimensional finite element model for the cutting process has been established to investigate the effect of cutting parameters on the deformation of 2A12 aluminum alloy thinwalled tubular parts.With the goal of minimizing the deformation,the range analysis method was adopted to obtain the optimized cutting parameters: spindle speed of 350 r/min,feed rate of 10μm,and cutting depth of 20μm.A cryogenic + oil bath aging treatment process was applied to control the residual stress generated during the heat treatment process of aluminum alloy thin-walled tubular parts.The deformation of the parts was reduced by 0.34 mm after the cryogenic + oil bath aging treatment,demonstrating the effectiveness of the process.