| Shape memory alloys are used more and more in the industrial field,but the lower cost Cu-Al type shape memory alloys have more obvious anisotropy between grains,which limits their industrial applications.Shape memory alloys will also be used in the field of fasteners,using their shape memory properties to connect plates.The Cu-Al alloy with a columnar crystal structure prepared by a special process can reduce the negative effects brought by the anisotropy between the grains and obtain better mechanical properties,shapes and properties.This article is based on the research work carried out by the research group in recent years in the "shape memory alloy fastener connection technology" project(project number: 61409230506).The research object of this paper is Cu-Al-Be alloy.The law of phase transition temperature and Be content of this alloy is determined,and the alloy composition with martensite transformation temperature of-50 ° C is obtained.Design and manufacture Cu-AlBe alloy rods with a large-diameter columnar crystal structure.Since the material needs to be reduced in diameter when the material is used as a fastener,the columnar crystal structure of the bar is axial,and the load direction during the diameter reduction is perpendicular to the growth direction of the columnar crystal grains.Therefore,the lateral compression properties of the columnar crystals at room temperature need to be studied.1.The Cu-Al-Be alloy was prepared by analyzing the phase diagram,theoretical calculations and experiments,and the phase transition temperature of the alloy was analyzed using a differential scanning calorimeter.2.Design and manufacture down-drawing Ohno continuous casting equipment that meets the experimental conditions.3.Through the use of universal testing machine,optical microscopic imaging system,scanning electron microscope,electron backscatter diffractometer and X-ray diffractometer,etc.,the compressive properties of the alloy at room temperature were tested,and its microstructure was characterized and observed.The composition is determined.The test results and analysis show that 1.The alloy composition required for the application is 11.79 wt% Al and 0.52 wt% Be,the martensitic transformation temperature of this alloy is-59 C,and the austenite transformation temperature is-53 ° C.2.Cu-Al-Be alloy materials with diameters of 8 mm and 12 mm were prepared by the down-drawing Ohno continuous casting equipment,in which the traction sped was 17-30 mm / min,the cooling distance was 10-15%,and the mold outlet temperature 1017 ? 1090 ° C.3.The compresive mechanical properties of Cu-Al-Be alloy with columnar crystal structure will be improved.When the load direction and columnar crystal growt h direction are parallel to each other,the material can withstand about 15% deformation before fracture,and when the load direction and columnar crystal gr owth direction are perpendicular to each other,the material can withstand about 40% deformation before fracture the amount.The columnar crystal structure can increase the total deformation of the alloy under compresive load.4.The Cu-Al-Be shape memory alloy of this composition will undergo about 50% martensite transformation when the loading is 4%,and its product is ? ? martensite with HCP structure.After unloading,the residual strain of the material will be automatically eliminated.When the loading is 16,a 96% martensitic transformation will occur.Heating the material after unloading can eliminate part of the recoverable residual deformation,but it will still exist on March 3.% Permanent residual deformation.Theoretically,the material can be used in fasteners.5.By loading,the alloy rod is reduced in diameter and placed in the hole.When the alloy is heated,the rod size can be partially restored,thereby interfering with the link and achieving tig htness.Solid application effect. |
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