Investigation On Process,Microstructure And Properties Of Wire Oscillating Laser Additive Manufacturing Of 2319 Aluminum Alloys

High-strength aluminum alloys such as Al-Cu series and Al-Li series are widely used in aerospace,high-speed trains,new energy vehicles and other fields due to their high specific strength and low density.However,the traditional aluminum alloy manufacturing methods have been difficult to meet more and more higher requirements,so it is urgent to develop new manufacturing techniques.As a new type of processing method,additive manufacturing is widely used in the manufacture of aluminum alloys.At present,the additive manufacturing of aluminum alloys is dominated by SLM and WAAM.SLM has high precision and is more suitable for the manufacture of small parts.WAAM has high deposition efficiency and good uniformity which is suitable for making large parts,but suffers from high porosity and high heat input.Laser deposition can effectively reduce heat input,but it is prone to problems such as process instability and pores.In order to reduce the heat accumulation during deposition at the same time reduce the defects and difficulties of conventional laser deposition,a new method of oscillating laser beam deposition with filler wire was proposed in this thesis.Taking filler wire ER2319 as the basic material,good deposition process results were obtained through optimizing process parameters,and deposition samples of aluminum alloy2319 were prepared with smooth surface and extremely low porosity.The effect of process parameters on formation with different laser beam oscillating modes was studied,and the porosity distribution and microstructure properties of the deposited samples were explored as well.The influence of heat treatment on the microstructure and properties of the samples was studied.The results showed that,compared with the non-oscillating laser,the oscillating of laser beam can reduce the pores and increase the stability of the deposition process which in one word improve the formation features and obtain a well-shaped deposition pass.In different laser beam oscillating modes,the circular oscillating and infinity shaped oscillating can obtained the preferable deposition surface,and no pores were found.The heat input per unit volume of no oscillating,circular oscillating and infinity shaped oscillating was27.35 J/mm³,12.40J/mm³,and 20.82J/mm³respectively.The circular oscillating has minimal heat input,which is beneficial for obtaining samples with better formation and properties.The effect of the overlap ratio on the forming was studied.When the lap ratio was set to 50%samples obtained was smoothest,which showed that this ratio can made a good multi-layer deposition.As the number of deposition layers increases,the pores increases and finally the formation was gradually stabilized.The conditions of circular oscillating,50%overlap ratio and 0.7mm focus spot lift step were preferred for deposition.Samples of single layer had coarse microstructures at the lap joints while with the transiting from columnar to cellular from bottom to top area.Samples of multi-layer was dominated by columnar crystals inside the deposition unit with equiaxed crystal layers at the bottom and inside area.The heat-affected range of the deposited layer was three layers with total height of about 2.2 mm.The size of the deposition sample was120mm×32mm×10mm,with a total of 40 layers were deposited and 6 passes taken per layer.The surface of the sample was smooth and flat without obvious macroscopic defects.The porosity was lower than 1%.The pores were mostly located at the interface between the deposition unit and the advanced layer.The interior of the deposition unit was dominated by columnar crystals,and there was an equiaxed layer at the bottom and between the columnar crystals.The top columnar crystals tend to be coarsened and equiaxed.A large number of second phases were precipitated at the grain boundaries in the form of dots,rods and networks.The average microhardness was 87HV_0.2 and there were some differences in the microhardness values of different passes.The tensile strength was 245-265 MPa and the elongation was 12.6%.There are no obvious anisotropy was exhibited.The fracture form is mainly microporous polymeric fracture.After heat-treated,the grain morphology showed no change.The inner equiaxed grain layer disappeared,and the grain size was increased about 20%.Theθphase dissolved in a large amount,which improved the segregation of elements and improved the precipitation hardening effect.Theθ′phase was dispersed in needle-like and short-rod-like shapes.The microhardness was increased to 153HV_0.2which was equal to 76%in ratio,and the differences between passes were eliminated.The tensile strength was425-440MPa,the elongation was 10%which increasing by more than 50%in ratio.The tensile fracture was a composite type of fracture dominated by cleavage fracture.Compared with the deposited samples obtained by WAAM after the same heat treatment,the tensile strength was increased by about 10%,and was about 4%higher than that of 2219-T6 which was 415MPa.The strength was improved significantly.