Research On Galvanic Corrosion And Protection Technology Of Dissimilar Metals

In the process of developing and utilizing the ocean,it is inevitable that the contact of dissimilar metals in marine environment,which will cause serious galvanic corrosion.Aiming at the problem of galvanic corrosion in the marine environment,this article explores the galvanic corrosion behavior and mechanism of three typical dissimilar metal galvanic pairs:30CrMnSiA high-strength steel/5083 aluminum alloy,30CrMnSiA high-strength steel/TC4 titanium alloy and 5083 aluminum alloy/TC4 titanium alloy.To solve the problem of galvanic corrosion,exploratory study ongalvanic corrosion protection of laser cladding technologywasconducted.The galvaniccouples are corroded mainly through three kinds of simulated environmental corrosion tests:full immersion,salt spray,and full immersion-salt spray cycle.Theelectrochemical parameterssuch as galvanic current,galvanic potential,potentiodynamic polarization curve,impedance spectroscopy,etc.on samples with different corrosion periodsweretestedbyelectrochemical workstation.The micro-morphology of surfaceofsamples,the element distribution and phase composition of corrosion products were observed and analyzed by XRD,SEM and EDS.The main conclusions as follows:(1)The three types of galvanic couples had severe galvanic corrosion in three corrosive environments.The current density of the galvanic coupleswereall greater than 10 μA·cm-2,and the galvanic corrosion sensitivity ratings have reached theElevel.They cannot be directly contacted and used in the marine enginering.If they need to be contacted and used,they must be protected.The salt spray corrosion environment has much greater corrosion damage to materials than the full immersion environment,mainly because the contentof dissolved oxygen of the liquid film on the metal surface was sufficient in the salt spray environment,which wasconduciveto the smooth progress of the oxygen reduction process of the cathode reaction in the galvanic corrosion.(2)Among the three metals,the corrosion potential of 5083 aluminum alloy(about-0.76V)<30CrMnSiA high-strength steel(about-0.56V)<TC4 titanium alloy(about-0.43V).In simulated corrosive environments.Oxide layerswere produced on the surface of 5083 aluminum alloy,but it was unstable,pronedto pitting corrosion,and there was also a tendency to local corrosion;30CrMnSiA steel was severely corroded even if itwas used as cathode due to its own inability to corrosion.The inner and outer rust layers are formed on the surface of steel,butthey still cannot resist the corrosion of Cl-,causing the oxide layers to crack or even peel off,and the degree of corrosion continued to exacerbate.TC4 titanium alloy had a dense,stable and self-healing passive film formed on its surface,and hadexcellent corrosion resistance with very slight corrosion marks.(3)Using laser cladding technology to prepare Ni-Cr-Mo series and Cu-based alloy cladding layers on the surface of 30CrMnSiA high-strength steel and 5083 aluminum alloy substrates,which broke through the limitations of the existing galvanic corrosion protection technology,and the prepared alloy cladding layers had excellent corrosion resistance.The electrochemical results showed that when the steel and aluminum with the cladding layer are coupled to each other,or they are coupled to titanium alloy or 316L stainless steel,the galvanic corrosion current density is less than 0.3μA cm-2,and the galvanic corrosion sensitivity reached A level.The existence of the laser cladding layer had a good protective effect on the substrate and they can be used directly.