Experimental Study On Creep Aging Behavior And Constitutive Modeling Of2124Aluminum Alloy

With the development of modern aerospace technology, it has been put forward a great deal of requirements on aircraft performance. In order to meet these requirements, more and more main load-bearing parts of aircraft such as the connector, beams, partitions and wing box are using integration structure design. Creep age forming technology has been developed as a new technology as it can produce large integral panel components. Nowdays, this technology is considered as one of the important forming technology for the next large civil aircraft, as it will have a wide application prospect in "Large Aircraft", such as airliner and large military transport in our country.In foreign countries, creep age forming technology has been used in aircraft wing panel production in the middle of1980’s, and achieved notable accomplishment. Up to now, it has not been used in engineering application, the main reason is the lack of basic research and technical reserve in this area.2000series and7000series aluminum alloys have the most application of wrought aluminum alloy in aerospace. As2124aluminum alloy with good toughness and fatigue properties, particularly suitable for the site with high requirements on strength and stability at an intermediate temperature, so it takes the2124aluminum alloy as the research object in this paper. It have been systematically studied the effect on microstructure and mechanical properties by uniaxial tensile creep aging under different technological parameters, researched the creep deformation mechanism and established the creep constitutive model of the alloy. The main work and results are as follows:(1) It compares and analyzes the effect on microstructure and properties of2124aluminum alloy by creep aged under stress and conventional ageing with stress-free, found that the creep ageing under stress accelerates the aging process, shortens the peak ageing time, and improve the peak strength of2124aluminum alloy at the certain test condition; there was no precipitation preferentially precipitated along one direction, that is to say, not observed clear stress orientation effect, which has provided the theory support for the industrial application of2124aluminum alloy age forming technology.(2) The effect on creep behavior, microstructure and properties of2124aluminum alloy have been systematically studied at aging temperature(185.190&195℃), aging time(1～12h) and test stress(200,225&250MPa). The results show that:①The creep behaviors of2124aluminum alloy exhibited the first and the second stages of the typical creep curve with the supplement levels, that is the decelerating creep stage and the constant creep stage; aging temperature, ageing time and test stress were the important factors for the creep behavior of2124aluminum alloy, the creep behavior reinforced with the increasing of aging temperature, aging time or test stress.②At the same ageing time and test stress, the property of2124aluminum alloy showed certain changing tendency with the increasing of ageing temperature. When aged at lower stress(200MPa), the strength increased firstly and then declined, while elongation decreased gradually; when aged at higher stress(225MPa,250MPa), the strength and elongation decreased with the increasing temperature.③At the same ageing temperature and test stress, the typical three aging stage:under-aged stage, peak aging stage and age stage of2124aluminum alloy were appeared in creep ageing process, with increase aging time. The best property was achieved at aged8h, with the main strengthening precipitation S" phase and S’phase; prolong ageing time to12h, the property declined for the alloy in over ageing stage, in addition to precipitation S" phase, S’phase, there also some large S phase.④At the same aging temperature and aging time, the property of2124aluminum alloy showed certain changing tendency with the increasing test stress. When the temperature reached185℃, the properties of alloy decreased firstly and then increase, with the increase of test stress; while the temperature reached190℃or195℃, the properties of alloy decreased with the increase of test stress.(3) A creep ageing mechanism is tentatively suggested. Basing on the analysis of the apparent stress index and apparent activation energy of 2124aluminum alloy under certain condition, and according to the typical creep mechanism,it obtained that the creep mechanism is mainly on dislocation climb.(4) Established a constitutive model for creep aged2124aluminum alloy. Based on the inverse problem numerical theory, it established the constitutive modeling of2124aluminum alloy with tensile creep data. The constitutive modeling could describe creep behavior of2124aluminum alloy well under the experiment condition, through the validation and analysis of the constitutive model.