Research On Forming Characteristics Of Thin-wall Aluminium Alloy Parts By Laser Assisted MIG Arc Additive Manufacturing

Arc welding-based additive manufacturing(AM)technology,using welding arc as theheat source and wire as the consumable material,can fabricate the complex functional metallic products with high density and mechanical properties rapidly.This technology also has the advantages of high deposition rate and high material utilization.With the purpose of improving the deposition stability and the mechanical properties ulteriorly,the low power pulsed laser assisted MIG arc welding technology is applied into AM process.Based on this innovative AM method,researches on forming dimension,surface quality,microstructure and properties have been carried out on ER5356 aluminium alloy thin-wall parts.Firstly,the effects of single process parameter on forming dimension of the thin-wall parts stable region were studied.The layer width and height increase as the increase of welding current,and decrease along with the deposition velocity.And the layer width decreases as the inter-layer temperature,the layer height changes oppositely.However,the forming dimension changes not significantly with laser power.When the laser power ranges from 0 to 400 W,the layer width would decrease slightly due to the effects of laser-induced attraction and constriction of MIG arc.At the same time,we built up the evaluation system for forming quality based on the calculation of surface roughness and material utilization.And the effects of single process parameter on forming quality of the thin-wall parts were studied.The increase of welding current and inter-layer temperature,as well as the decrease of deposition velocity,would all lead to a high surface roughness and a low material utilization.The forming quality changes not significantly with laser power.The surface roughness of thin-wall parts under different laser powers were all less than 0.2 mm,and the material utilization were all more than 90%.In order to meet the needs of practical engineering applications,further study of forming dimension of the thin-wall parts stable region,a prediction model was developed between the dimension(width,height)and process parameters(welding current,deposition velocity,laser power and inter-layer temperature),based on the quadratic general rotary unitized design.The results of the model analysis showed that the dimension prediction model has high accuracy,the forming dimension can be controlled effectively through adjusting the parameters according to the model,and the purpose of process parameters systematized can be achieved.Then the microstructure and mechanical properties of the thin-wall parts were studied.It is found that there was element segregation behaviour in the deposition parts.The microstructure of the top region mainly consists of equiaxed gains and columnar gains,in the layer bands and bottom region the microstructure mainly consist of dendritic grains.There also existed wave-shape layer boundaries in the cross-section of the thin-wall parts.The microhardness decreased along with the deposition height increases,ranging from 93 HV to74 HV.Tensile test showed that the fracture was ductility,the average tensile strength of horizontal direction was 281.8 MPa,the average elongation was about 26%.For the vertical direction,the average tensile strength was 271.3 MPa,the average elongation was about 22%.What's more,for the samples in the horizontal direction,the top region existed the highest tensile strength,which was about 287 MPa.The surface quality improved significantly by adding laser with other parameters being equal.The width and height difference reduced obviously while adding the low power laser,both the standard deviation decreased by more than 50% when the laser power was 200-400 W.At the same time,the tensile strength increased more than 10% compared with the normal GMAW-based AM process.Finally,based on the low power pulsed laser assisted MIG arc additive manufacturing system,an arc-shaped frame structure part with the length of 50 cm was deposited.The forming part existed no relevant defects,and the dimension error rate was controlled at lass than 5%.