| Adding a small amount of Ag to Al alloy,it can improve the micro-structure and properties of Al alloy.The selective interaction of Ag element and vacancy leads to the decrease of the diffusivity of solute atoms in the alloy matrix,and it accelerate the nucleation rate of precipitated phase in Al alloy.At the same time,it also limits the formation of dislocation rings during quenching and aging.The position of non-uniform nucleation of precipitation phase in aluminum alloy is reduced.At present,the research on the precipitation mechanism and microstructure evolution mechanism of trace elements added in Al alloy is a little insufficient.Therefore,the study of Al Ag alloy is very important.Because the radius of Al atom is similar to that of Ag atom,the precipitation of Ag atom has little effect on lattice distortion.In this paper,Al-Ag alloy is selected as the experimental material.Micro defects are made by quenching and cold rolling.Aging treatment was used to promote the precipitation of Ag atoms in the sample.By using the "Self-Searching" feature of positron annihilation technology,the defects and precipitates in the metal were characterized.Then the precipitation mechanism of Ag atom in Al Ag alloy and the intrinsic mechanism in Al alloy can be obtained.Through the study of the interaction behavior and influence between different defect types and alloy components in Al Ag alloy,the main contents and conclusions of this paper are as follows:1.After quenching,natural aging will begin immediately.There will be a "quick response" in the short term,then a "slow response" occurs over a long period of time.In the "fast reaction" stage,the Ag atom will gather rapidly and form nucleus,and most of the vacancy will be recovered in this process.This is because the slow effect of precipitation kinetics helps the precipitated Ag in Al-Ag alloy go through a complete remodeling process and establish a new equilibrium state.2.At room temperature,the quenched sample reached initial stable state after 24 hours of natural aging.The low temperature positron annihilation technique,which is very sensitive to Ag precipitates,was used to detect and analyze the Al Ag alloy at low temperature(10-293k).The results show that: When the temperature reaches 10 K,the ability of Ag precipitate to capture positrons reaches the maximum.At low temperature,the binding energy between Ag precipitate and positron depends on the size of Ag precipitate,the smaller the size,the lower the binding energy.At the same time,the smaller the size of Ag precipitate is,the shallow trapping effect is more obvious with the change of temperature,the more temperature dependent.3.Dislocation type defects were introduced into Al Ag alloy by cold rolling.And then in-situ positron annihilation technique is used to detect and analyze the natural aging process of deformed samples at room temperature.The results show that: the strength of defects decreased slightly,some of the vacancies are recovered by means of migration,In the process of migration,a small number of vacancies will merge with other vacancies and aggregate to form a large-scale vacancy cluster;The difference of the shape variables of Al-Ag alloy with the same composition will not have a very obvious effect on the Ag precipitates.Then,the Al-Ag alloy with 10% deformation was annealed at 423 k for one hour,the low temperature positron annihilation technique was used to detect and analyze the Al Ag alloy.The experimental results show that:the strength of capture positron force depends on their physical state,distribution and type.The binding energy between Ag precipitate and positron is related to its size,while the binding energy between dislocation and positron is almost constant. |
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