Study On Improving Dimensional Stability Of Light-Alloy Components By Deep Cryogenic Treatment

High strength aluminum alloys have been widely used in weapon systems due to their high strength-to-weight ratio, excellent corrosion resistance, and high fracture resistance. But, the precise aluminum components have low percent-of-pass during machining process, loss the precision during resting period and would not be reliable during application period because of the dimensional instability which was induced by residual stress and the instability of microstructure. Therefore, it was significant to control and eliminate the residual stress and improve the stability of microstructure for precise aluminum components. Supported by No. xx Institute of China Ordnance Industry, the variation of residual stress was investigated by numerical simulation method, and the metallographic analysis were carried out with cryogenic treatment part and conventional treatment part. The main works done as follows:First, FEM method was introduced to calculate the transient temperature and stress field. The mechanical model of deep cryogenic process was established by thermal elasto-plastic theory, the boundary conditions were analyzed during every step, the thermo-physical properties were calculated by interpolation method, and lastly, the technological process of numerical simulation was concluded.Second, the cryogenic treatment of high strength aluminum component was researched. The transient temperature field was simulated during different period, the stress field was calculated by sequentially coupled thermal-stress analysis, and the residual stress was investigated. The simulated results showed that: the residual stress of cone-shaped part reduced 20.4%, 17.9% and 16.1% respectively after the three different cryogenic processes; the residual stress of cartridge receiver part eliminated 23.7%, 15.3% and 14.1% respectively.Third, the effect of cryogenic treatment on dimensional stability during machining was investigated. The material removal models of aluminum parts were established, and the material removal process was simulated with cryogenic treatment part and conventional treatment part. The simulated results showed that: the machining-induced distortion of cone-shaped part reduced31.9% after cryogenic treatment; the distortion of cartridge receiver part eliminated 13.7% after cryogenic treatment.Last, the metallographic analysis of high strength aluminum alloy with different treatment were carried out for investigating about the effect of cryogenic treatment on microstructure by metallomicroscope and SEM , the SEM picture showed that plenty of dislocations were produced by cryogenic treatment. The dislocations need more energy when it distorted, so the microstructure was more stable, and the dimensional stability of precise aluminum component was improved.