| Silver alloy electrical contact materials have excellent electrical conductivity,thermal conductivity,oxidation resistance and welding resistance,and are widely used in aerospace,modern transportation,household appliances and other industries.In recent years,with the development of electronic devices towards miniaturization,low energy consumption,high precision and long life,higher requirements have been put forward for the comprehensive properties of silver alloy electrical contact materials.The aim of this thesis is to develop new in-situ composite silver alloy electrical contact materials with β-Cu(Ag,Ni)fibres.Firstly,the data-driven machine learning method is used to design the composition of silver alloy electrical contact materials,so as to quickly obtain the composition design scheme that can improve the mechanical and electrical comprehensive performance and reduce the research and development cost.Then,the method of reasonable matching of plastic deformation and heat treatment is adopted to further improve the microstructure homogeneity,strength and electrical conductivity of the alloy,and the evolution law of the alloy microstructure and properties during the preparation process is clarified.Finally,the electrical contact behavior and degradation mechanism of silver alloy electrical contact materials are clarified through the study of different performance matching and service conditions of the alloys.The main results are as follows:A machine learning model for the relationship between composition and properties of silver alloy electrical contact materials was established,and a multiobjective optimization algorithm was introduced to rapidly optimize the composition of silver alloy.Three kinds of silver alloy electrical contact materials Ag-19.53Cu-1.36Ni,Ag-11.40Cu-0.66Ni-0.050Ce and Ag-10.2Cu-0.2Ni-0.056Ce were designed.The results of the experimental validation under industrial conditions show that the mechanical and electrical comprehensive performance of the three designed alloys is better than the existing silver alloy electrical contact materials,and the error between the predicted and measured performance is less than 10%.Taking the Ag-11.40Cu-0.66Ni-0.050Ce alloy with good performance matching as the research object,the microstructure of the in-situ composite βCu(Ag,Ni)short fiber-reinforced alloy was designed by the method of "Cu(Ag,Ni)supersaturated precipitation+severe plastic deformation drawing".After heat treatment at 200-600℃,the fiber microstructure of the alloy is not completely damaged.The electrical conductivity can be adjusted in the range of 78.691.9%IACS,and the Vickers hardness can be adjusted in the range of 84.1-169.3 HV,meeting the requirements for electrical conductivity and hardness of electrical contact materials in different application scenarios.The arc erosion experiment of in-situ composite short fiber-reinforced silver alloy shows that the arc erosion mechanism and material transfer direction of the alloy change with the increase of load current.Under 10 A load current,the arc erosion is mainly the ionization and evaporation of anode metal under the action of short arc,and the material transfer direction is from anode to cathode.When the current increases to 12 A or above,the arc erosion is mainly caused by the gas ions bombarding the cathode under the action of long arc,and the material transfer direction is from cathode to anode.Under the experimental conditions in this paper(voltage 24 V DC,current range 10 to 20 A,20,000 switching operations),the maximum mass loss of the alloy is only 0.76 mg,showing excellent arc erosion resistance.A study of the sliding electrical contact behaviour of in-situ composite short fiber-reinforced Ag-11.40Cu-0.66Ni-0.050Ce alloy(pin)-brass(disc)shows that the current-carrying frictional wear mechanisms of the alloy are dominated by adhesive wear,arc erosion and oxidative wear.The change of load conditions significantly changes the proportion of arc erosion and adhesive wear.Under the experimental conditions in this thesis(current range 0 to 4 A,load range 6 to 14 N),the friction coefficient of the alloy in the stable wear stage fluctuates in the range of 0.71-0.91,and the wear rate fluctuates in the range of 15.0×10-5 to 39.3×10-5 mm3·N-1·m-1.This indicates that the prepared alloy in this study is a sliding electrical contact material with higher stability and better wear resistance. |
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