Study On Micro-arc Oxidation Treatment And Corrosion Resistance Of Ti6Al4V Alloy Fabricated By Powder Bed Additive Manufacturing

Additive manufacturing technology has the advantage of rapid forming of complex geometries,and is a hot spot for research in the field of materials in recent years,among which the proportion of Ti6A14V alloys prepared by additive manufacturing reaches more than 50%.The rapid solidification thermal processing history unique to additive manufacturing technology causes defects such as high surface roughness,poor fusion and microstructure disorder of Ti6A14V alloy.Particularly serious is the unmelted powder adhesion on the surface of the formed parts and the step effect resulting in high surface roughness,resulting in a serious decline in fatigue performance and corrosion resistance of the deposited parts,which has become one of the bottlenecks for large-scale industrial applications.At present,the conventional surface treatment technologies such as chemical,electrochemical and turning processes cannot fully meet the demand for improving the surface defects of titanium alloy complex-shaped parts prepared by additive manufacturing technology.To solve the above problems,this paper adopts MAO(Micro-Arc Oxidation)technology to conduct Selective laser melting under constant pressure and constant current mode respectively.The surface of the original deposited Ti6A14V alloy prepared by SLM technology and Selective electron beam melting(SEBM)technology was treated comprehensively.The effects of phase composition,surface morphology,thickness and surface roughness on the corrosion resistance of the film were systematically studied.The main research results are as follows:(1)The phase compositions of the deposited SLM and SEBM specimens are(?+?')and(?+?);the phase compositions after constant-flow mode microarc oxidation treatment are anatase phase,rutile phase and TiO2 of Srilankite phase,and the coexistence of the three phases has a more stable structure than the constant-pressure mode microarc oxidation treatment which only produces anatase phase and rutile phase TiO2.(2)MAO treatment attenuated the step effect on the original specimen surface,and the surface roughness Ra of the SEBM specimen was reduced from 28.803 ?m to 10.535 ?m at maximum in the constant-flow mode,and the surface roughness Ra of the SEBM specimen was reduced to 8.902 ?m at maximum after the pre-polishing combined with MAO dual surface treatment;the surface roughness Ra of the SLM specimen was increased from The surface roughness Ra of SLM specimens in constant flow mode increased from 8.49 ?m to 8.777 ?m at the minimum,and the surface roughness Ra of the film layer increased to 9.163 ?m at the minimum after pre-polishing combined with MAO double surface treatment.(3)The MAO surface treatment improved the corrosion resistance of the original specimens,and the SLM specimens had better corrosion resistance in constant current mode microarc oxidation,while the SEBM specimens had better corrosion resistance in constant pressure mode.the corrosion current density Icorr of the SLM specimens decreased from 6.212×10-5 A/cm2 to 1.532×10-5 A/cm2(t=15min),so that the Icorr reduction of SEBM specimens from 5.04×10-5 A/cm2 to 1.359×10-5 A/cm2(U=420V),pre-polishing+MAO double surface treatment of SLM and SEBM surface film layer of the film layer of Icorr reduced to 2.493×10-7 A/cm2(t=15min)and 1.672×10-6 A/cm2(U=400V),the smaller the corrosion current density,the better the corrosion resistance.