Microstructure And Tensile Properties Of QAl9-4 Copper Alloy Deposited By Electron Beam Freeform Fabrication

QAl9-4 copper alloy has excellent corrosion resistance and wear resistance,weldability,excellent mechanical properties and machining properties,widely used in gears,bushings and ship propellers.Compared with the traditional casting process and the selective laser melting technology,the electron beam fuse deposition technology has the advantages of forming large parts,higher material utilization,fast printing speed,forming high melting point materials,and vacuum environment processing without introducing pollution,which makes the electron beam freeform fabrication technology has a greater advantage in the preparation of copper alloys.In this study,the QAl9-4 copper alloy as the research object,under different deposition process parameters of the forming alloy macro morphology,molten pool characteristics,microstructure and tensile properties were carefully studied.Firstly,the effects of different process parameters on the macroscopic morphology,phase composition and microstructure of the sedimentary body were studied.As the beam density increases,the width of the deposit increases,but the height decreases;with the increase in printing speed,the width of the deposit decreases,and the height is basically unchanged;when the wire feeding speed increases,the height and width of the deposit increase slightly.The study found that the central part of the sediment is mainly distributed with the original?columnar grains epitaxially grown along the deposition direction,and then the fine?grains are precipitated,and the original columnar crystals can pass through several,the size of a deposition layer increases with the increase of the deposition height of the sample.In the deposit,the?_Iphase did not precipitate due to the fast cooling rate,the?_IIphase precipitated between the dendrites,and the nano?_IVphase co-precipitated in the?matrix,and there was a strict orientation relationship with the?-Cu matrix.The orientation relationship is(200)?-Cu//(110)?_IV,[001]?-Cu//[001]?_IV,and no retained?phase is observed in the middle of the sediment.The deposited alloy exhibits a fine equiaxed crystal structure and a relatively weak texture.Finally,the influence of different process parameters on the tensile properties of the deposited alloy is studied.The study found that fine-grain strengthening,solid solution strengthening,and precipitation strengthening are the main strengthening mechanisms of QAl9-4 aluminum bronze alloy deposited by electron beam fuse.As the beam density increases,the tensile strength of the alloy in the middle of the deposit increases.When the beam density is larger,the strength does not increase due to the solid solution limit.When the beam density is 35m A,the maximum tensile strength is 621.220MPa.As the printing speed and wire feeding speed increase,the tensile strength of the deposit alloy increases.The elongation of the deposited alloy under all process parameters is about 30%,and the toughness is relatively good.In the Z direction,the tensile strength of the deposited alloy first decreases and then increases,the maximum tensile strength of the bottom of the deposit is 672.563MPa;the elongation first increases and then decreases,and the highest elongation in the middle of the deposit is 30.1973%.The hardness of the deposited alloy also shows a trend of first decreasing and then increasing in the Z direction.The hardness of the chilled zone at the bottom of the deposited body is the highest at 195HV,and the hardness of the thermal cycling zone in the middle of the deposited body is the lowest at 138HV.