Effect Of Cold Deformation And Aging On Microstructures And Mechanical Properties Of 2219 Aluminum Alloy

Due to the restriction of observation and experimental technology,the creep crack propagation experiments are mostly based on two-dimensional surface cracks in the past 30 years.However,the damage detected on the surface is different from that in the interior of the bulk due to stress-strain difference.Hence,it is necessary to perform analysis of 3D crack propagation.Grain orientation,grain size and second-phase particles which influence each other are the main contents of the 3D crack propagation study.In order to reveal the interaction of the micro cracks and grain boundary,specimens with a stable grain size and the second-phase are need.In this work,2219 aluminum alloy was selected as the experimental raw material.Samples with different grain size,aging state and special grain boundary structure were prepared for future three-dimensional crack research.The raw materials used in the experiment contain coarse second-phase Al2 Cu.In order to avoid the formation of microcracks in the second-phase during the rolling process,solution treatment,which is also necessary for the subsequent aging treatment,should be done at first.The results show that the optimum process is heating at 535℃for 5h.Less amount of residual second-phase in the alloy is found and the hardness increase after the solution treatment.Under the same recrystallization annealing conditions,grains of different sizes were obtained by changing the amount of cold rolling.After cold rolling deformation,the grain boundary of the alloy is overlapped,the number of special grain boundaries in the grain boundary increases and the type of special grain boundary turn to low Σ value.The optimal recrystallization process for the alloy of two kinds of deformation is heating at 520 ℃ for 1h.After recrystallization processing,2219 aluminum alloy with homogeneous and refined grains can be obtained.With the increase of the aging temperature,the coarse disk-like precipitates with chainlike distribution in the alloy gradually gathered to the grain boundary.As aging temperature rises to 350℃ the disk-like precipitates transform to lamellar structure.With the increase of aging time at 350℃,the laminar precipitates gathered and grew up.Under the same aging conditions,precipitates will be fine dispersed in specimens with high cold-rolling rate,the reason is that the bigger deformation suppresses the precipitation of the G·P region and the θ phase and promotes the formation of the θ’ phase.It’s shown that the microstructure and mechanical properties are most stable when aging 20 h by microstructure morphology and Vickers hardness analysis of aging aluminium alloy,and it’s also shown that the higher coldrolling rate is,the more stable will be.The tensile test show that the mechanical properties of the alloy with higher cold-rolling rate are better than low cold-rolling at the same aging temperature for 20 h.