| High-end equipment has put forward higher and higher requirements for the strength,toughness,corrosion resistance,fatigue resistance,and machinability of aluminum alloy materials.The components of advanced equipment adopt the overall structure of the high performance,low density,and high reliability.It has been difficult to meet the high-efficiency and low-cost manufacturing requirements of large-scale aluminum alloy components with complex structures by relying on traditional casting,forging,and machining methods.The emergence of additive manufacturing technology can effectively solve the above problems.In this paper,based on studying the wire arc additive manufacturing of aluminum alloy,the basic problems of pore control by heat treatment and external energy field assistance are studied given the hole defects in the wire arc additive manufacturing process,and the following main research results are obtained.(1)The influence of four process arc modes on forming was studied,and it was found that the porosity was CMT-PADV,CMT,CMT-P,and CMT-ADV in order from high to low.The optimal travel speed range corresponding to different wire feeding speeds was determined.It is found that the forming adaptability is mainly related to the flow mode of molten metal,which is affected by the surface tension of liquid metal,the viscosity of liquid metal,and the filling amount of welding wire per unit time.(2)The intrinsic relationship between process parameters and porosity,microstructure,and mechanical properties was studied,and it was found that with increasing heat input,porosity increased.And there are micron pores at the grain boundary.The porosity of the samples obtained in the experiment is between 1% and 5%.The formation mechanism of pores is summarized into four parts: nucleation-growth-detachment-dissipation.The top of the thinwalled sample has an equiaxed crystal morphology,and the middle and bottom are columnar crystals and dendrites.The microhardness gradually decreases from 76 HV to about 50 HV from the top to the bottom,and the average tensile strength of the sample is about 190 MPa,the anisotropy is not obvious.(3)It is found that the heat treatment method can effectively solve the problem of uneven distribution of tissue and composition of aluminum alloy wire arc additive manufacturing specimens.After heat treatment,the pores tend to aggregate and expand,the porosity in the top area reduced to 0.24%,and the microhardness increased to 135% which is higher than that of the wire arc additive manufacturing sample.Tensile strength increased by about 35%.(4)The effects of laser energy field assistance on the forming process,porosity,microstructure,and mechanical properties of aluminum alloy samples are studied.It is found that the synergistic effect of the two is the best when the distance between the light wire is 1mm,but the porosity of the samples is high,which is mainly due to the stirring effect of the laser on the molten pool,which absorbs more hydrogen.The top layer of the sample is an equiaxed crystal microstructure,and there are columnar crystals in the middle and bottom layers.The microhardness is higher at the top and in the middle part,and the bottom is lower,which is about 20% higher than that of the arc sample.(5)It is found that the ultrasonic energy field auxiliary arc fuse additive manufacturing method can effectively eliminate large pores,and the average size of pores is from 100 μm reduced to 10-40 μm.The vibration effect and sound flow effect of ultrasound can promote the flow of the molten pool,which is conducive to the escape of pores,effectively reducing the porosity,and the porosity is reduced from 2.2% to 0.7%.the microstructure of the specimen appears in a significantly refined area,which is caused by the ultrasonic cavitation effect increasing the local supercooling degree of the molten pool.The precipitates in this area are dense,and the microhardness increases significantly,which is about 54% higher than that without ultrasonic. |
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