| Aluminum is a light white metal with abundant resources and accounts for the largest amount of non-ferrous metals used in the packaging industry.The addition of copper and magnesium can further increase the strength of packaging materials and improve processing performance.Existing traditional aluminum alloys have common defects such as poor strength and toughness,in-uniform micro-structure,and difficult structure adjustment,which can hardly meet the service requirements under extreme conditions.In order to expand the application of Al-Cu-Mg alloy in special military packaging,it is necessary to develop a new type of aluminum alloy that meets the requirements of high strength,high toughness and corrosion resistance at the same time,to replace traditional steel,copper,and titanium materials,and achieve the purpose of reducing weight,cutting costs,and improving the equipment performance.The spray forming rapid solidification fine-grained Al-Cu-Mg alloy is chosen in this paper,followed by different rapid cold punching severe plastic deformation.The microstructure evolution,precipitate behavior and the mechanism of dislocation movement in the Al-Cu-Mg alloy during deformation and heat treatment have been systematically analyzed by the atomic resolution transmission electron microscope（TEM）,scanning transmission electron microscope（STEM）,and mechanical properties tests and other characterization methods.The mechanism of the re-dissolution during the rapid cold punching and re-precipitation behavior during the aging process of the precipitates in the Al-Cu-Mg alloy are focused.The relationship between the precipitation sequence and process parameters（the degree of deformation and the aging temperature）is explored.The influences of pre-deformation,aging temperature and aging time on the mechanical properties of the alloy is analyzed.The strengthening and toughening mechanism of the Al-Cu-Mg alloy by deformation and heat treatment process and nano-precipitation are also clarified.At the same time,the rapid cold punching Al-Cu-Mg alloy anodizing process was explored,so as to lay a certain foundation for expanding the application of Al-Cu-Mg alloy in special packaging.The main conclusions obtained in the thesis are as follows:（1）The evolution rules,the fracture and re-dissolution mechanisms of the precipitated phases in the spray-formed fine-grained Al-Cu-Mg alloy during the rapid cold punching severe plastic deformation is analyzed.The difference in re-dissolution speed between the S’phase and theθ’phase under the same deformation conditions is also discussed.The results show that the main precipitated phases in as-extruded alloy are S’phase andθ’phase.During the rapid cold punching process,the precipitated phases basically re-dissolve under the combined effects of distortion,brittle fracture,re-dissolution and necking.In the matrix.The increases of contact surface between phases and aluminum matrix and the interface distortion energy caused by the brittle fracture of S’phase,resulting in the free energy of the S’phase being higher than the free energy of the matrix.The energy balance between the phase and the aluminum matrix creates diffusion conditions for the solute atoms to re-dissolve into the aluminum matrix.In addition,θ’phase is more stable than S’phase,and it is less prone to breakage and re-dissolution.（2）The influence of aging temperature and deformation pass on the hardness of timed samples is studied.Undergoing the same pass rapid cold punching,the samples aged at 180°C have the highest peak hardness,while no difference is observed on the peak hardness between the samples aged at 160°C and 200°C.At the same aging temperature,the peak hardness of the sample go upward with the increase of the rapid cold punching passes.The aging temperature and the passes are closely related to the aging response time;increasing the passes and the aging temperature can effectively shorten the time to reach the peak in the aging process.（3）After the re-dissolution,the re-precipitation behavior in the aging stage of the precipitated phase is analyzed.The main precipitate during the aging process is S’phase.When the aging temperature is high enough for completely eliminating the micro matrix lattice distortion produced by deformation,the precipitation sequence is the same as the conventional sequence;when the aging temperature is not enough to remove the high lattice distortion,the precipitation sequence would change and the GPB zone will be inhibited.When the ageing temperature is 180℃and 200℃,The GPB zone can still be observed in the peak ageing samples;the precipitation process of S’phase does not completely follow the order as the aging time;grain nucleation and growth may occur at any stage before the aging peak.As the aging time going,the S’phase get thicker,which is the main reason for the decrease of the hardness in the over-aging stage.（4）According to study the mechanical properties of Al-Cu-Mg alloys with different precipitation phase,the intrinsic relationship between the precipitation phase and severe plastic deformation and heat treatment process are found.The hardness of sample during the plastic deformation mainly depends on the combined the reduction caused by the precipitates re-dissolution and the increase due to work hardening.In the aging stage,the mechanical properties are mainly determined by the size,morphology and distribution of the precipitates.When the samples aged at 160℃,the tensile strength and yield strength of the sample with 2-pass rapid cold punching decreased compared with 1-pass;It is mainly due to the uneven distribution of dislocations causing the uneven precipitation of the S’phase,which weakens the precipitation hardening.After 4-pass rapid cold punching,the samples aged at 180℃for 2 h have the highest tensile strength and yield strength,which are 509 MPa and 393 MPa respectively.（5）The precipitation phase,grain morphology and the evolution of deformation band during rapid cold punching and recrystallization annealing were studied.The interaction between precipitation phase and recrystallization,the formation mechanism of deformation band and its effect on grain refinement were discussed.The results show that the precipitates of fine-grained Al-Cu-Mg alloy during rapid cold punching and recrystallization annealing mainly consist of S phase and a small amount of coarse Al6Mn phase.With the increase of deformation passes,the density of precipitates increases,the size of precipitates decreases significantly,and the deformation and transition bands disappear gradually.In addition,the grains are refined and tend to be uniform.Defects introduced by rapid cold punching contribute to the precipitation and recrystallization,and promote nucleation and growth of S phase and recrystallization.Deformation and transition bands in the coarse grains transform into deformation-induced grain boundary during the deformation and recrystallization,which refine grains,obtain uniform nanocrystalline structure and promote homogeneous distribution of S phase.（6）On the basis of the evolution and the strengthening mechanism of precipitated phases during plastic deformation and heat treatment,in order to improve the corrosion resistance of Al-Cu-Mg alloy,different heat treatment samples were anodized.The corrosion resistance of the anodic oxide film was tested on electrochemical workstation and the influence of heat treatment process and voltage on the corrosion resistance of the anodic oxide film was explored.The results show that the aging 180°C/2 h sample with the 35V voltage has the most excellent corrosion resistance and the maximum film thickness and hardness of 82μm and 432 HV,respectively. |
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