| Dimensional stabilizing techniques of 2024 aluminum alloy were investigated systematically. 2014 aluminum alloy was chosen for contrastive research. The effect of different heat treatment processes, such as uphill quenching, thermal-cold cycling treatment, aging and pre-stretching, on the dimensional stability was studied by measuring the dimensional change and the residual stress of the specimen. Microstructure of different state of 2024 aluminum alloy was researched using transmission electron microscope (TEM) technique. The relationship between microstructure and the dimensional stability is analyzed.The research of dimensional change before and after different heat treatment indicated that, compared with that of the natural aging and artificial aging 190℃/4h process, the dimensional change of uphill quenching and thermal-cold cycling treatment of 2024 aluminum alloy were reduced by 70%. The uphill quenching should be adopted before natural aging. Increasing the process number of uphill quenching could reduce the dimensional change of 2024 aluminum alloy specimens. As to thermal-cold cycling, it was found that the dimensional change of the longitude direction decreased while notch change of ring specimen increased, as the process number of thermal-cold cycling treatment increased. The biggest notch change of the circumferential direction accured when the 2014 aluminum alloy ring specimens were holding in 160℃for 16h,while the smallest was artificial aging 160℃/20h.As to notch change of the radial direction the biggest were natural aging process.The residual stress test results of 2024 aluminum alloy show that, compared with the natural ageing, the processes of artificial aging 190℃/4h and uphill quenching one time could reduce the internal residual stress of specimens by about 35%. However, thermal-cold cycling treatment and uphill quenching after natural aging couldn't reduce the internal residual stress of samples. When increasing the number of thermal-cold cycling to three the internal residual stress of the sample could be reduced, as to uphill quenching increasing the process had a unfavourable effect. Compared with conventional thermal-cold cycling process 190℃/4 h-liquid nitrogen/2 h, shorten the holding time in liquid nitrogen and extending that in 190℃would reduce residual stress of the sample. Thermal-cold cycling 190℃/5h-liquid nitrogen/1h process reduced residual stress of the sample by 50%. Machining before natural aging could reduce the residual stress of 2024 aluminum alloy by 75%, while 1.5% pre-stretching increase this percent for more 50%. The residual stress of 2014 aluminum alloy couldn't be reduced by machining before 160℃/20 h processing, while the residual stress could be reduced by 70% with the pre-tension deformation of 2%.The observation results of 2024 aluminum alloy microstructure show that the precipitated S phase, of which the number and size are moderate and the distribution is evenly, could be got when 2024 aluminum alloy was exposed to the treatment of artificial aging 190℃/4h and uphill quenching. While in the specimens of natural aging and T4-uphill quenching could not observe S phase. Observion of the 2024 aluminum alloy microstructure treated by thermal-cold cyclling shows that excessive and uneven distribution precipitation phase was formed. Many Cu-Mg atoms clusters whose dimensions are about 10 nanometers were observed in 2024 aluminum alloy pre-stretched specimens.Comprehensive consideration of the macro dimensional change, residual stress and the microstructure, the dimensional stabilizing processes of 2024 aluminum alloy include the uphill quenching one time, thermal-cold cycling 190℃/5h-liquid nitrogen/1h,1.5%pre-stretching. As to 2014 aluminum alloy the processes include artificial aging 160℃/20h and 2%pre-stretching. |
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