| Wire Arc additive manufacturing(WAAM)technology has promising development prospects in the manufacturing of large aluminum alloy components in aerospace industries owing to its low cost,high efficiency and high material utilization.However,WAAM aluminum alloys has problems such as poor forming accuracy,inhomogeneous microstructure,pores,residual stress and deformations.In this paper,low frequency vibration is introduced in the process of CMT additive manufacturing Al-Cu alloy to promote the grain refinement of deposition layers and reduce the porosity defects,so as to optimize the microstructure and properties of WAAM Al-Cu alloy.Firstly,the arc shapes and droplet transfers behavior under different CMT modes and the forming characteristics of single-pass single-layer and single-pass multi-layer under different WAAM parameters were studied.The results show that the CMT-PADV mode is more suitable for WAAM process of Al-Cu alloy.When the wire feeding speed is 4 m/min and the travel speed is 8 mm/s,the single-pass multi-layer deposited specimen is well formed,which can be used as a reasonable WAAM process for Al-Cu alloy.On this basis,the effects of vibration frequency and amplitude on the microstructure and properties of WAAM Al-Cu alloy were studied.The vibration frequency is adjusted by changing the revs of the exciter.The higher the speed,the greater the frequency.Three groups revs of 1200 r/min,3000 r/min and 4800r/min were selected respectively,and the control group without vibration was set up to study the effect of vibration frequency variation on the microstructure and mechanical properties of the WAAM 2319 aluminum alloy specimens.The results show that the fluidity of molten pool was improved with the increase of vibration frequency.When the revs was 4800 r/min,the average width of deposition layers increased by 5.3 %,the average layer height decreased by 8.8 %,and the cooling rate of the molten pool increased by 2 times.The mean grain diameter of the coarse grain region in the inner-layer zone decreased from 51.9 μm to42.0 μm,and the grain refinement degree reached 19.1 %.Vibration caused grain refinment in the microstructure of the deposition layer,and the refinment effect in the coarse grain region was significant.Vibration induced the molten pool to produce forced convection,and the neck and root of dendrite undergo fatigue fracture under dynamic bending stress and remelting.The generated dendrite fragments suppress the initial dendritic front growth and provide more nucleation particles,so as to achieve grain refinement effect.With the increase of vibration frequency,the texture intensity decreased,the texture orientation tends to be dispersed,and the proportion of high angle grain boundaries(HAGB)increased from 76.2%to 92%,indicating that the plasticity of the specimen was improved.The effect of vibration on the transverse and longitudinal tensile strength of the sample is not obvious,but the elongation after fracture increases significantly with the increase of vibration frequency.The elongations of transverse and longitudinal was the largest at 4800 r/min,reaching 22.2%and 23.5% respectively,which was 15.6% and 38.2% higher than that non-vibration specimen.The pore size on the fracture surface decreased,the distribution was more dispersed,and the dimple structure increased.It indicated that the increase of vibration frequency can effectively improve the plasticity of the WAAM 2319 aluminum alloy specimens.The amplitude is adjusted by changing the eccentric angle of the exciter.The greater the eccentric angle,the greater the amplitude.At 1200 r/min revs,three groups of angle values of 4°,8° and 12° and the control group without vibration were selected to study the effect of amplitude change on the microstructure and mechanical properties of the WAAM2319 aluminum alloy specimens.The results show that the increase of amplitude also improved the fluidity of the molten pool.When the eccentric angle is 12°,the average width of the deposition layer increased by 5.1%,while the average layer height decreased by 7.8%,and the cooling rate of the molten pool could reach 2.4 times that of the non-vibration specimen.The increase of the amplitude can effectively reduce the grain size of the coarse grain zone.When the deflection angle was 12°,both the transverse and longitudinal elongation values were the largest,which were 23.7% and 22.4%,respectively,which were23.4% and 31.8% higher than those without vibration.At the same time,its transverse and longitudinal tensile strength increased by 4.3% and 2.9% respectively,reaching 278.3 MP and 272.7 MPa.It shown that the increase of amplitude can effectively improve the strength and toughness of the WAAM 2319 aluminum alloy specimens.In summary,the application of low-frequency vibration with a certain frequency and amplitude in the process of CMT additive manufacturing Al-Cu alloy can effectively optimize the microstructure and mechanical properties. |
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