Research On The Microstructure And Corrosion Behavior Of Cold Sprayed Aluminum Alloy Coatings

Stainless steel is widely used in various industrial fields due to its excellent mechanical and corrosion resistance,such as ships,automobiles,aerospace,and offshore oil and gas platforms.Corrosion is a non-negligible problem in stainless steel applications.The corrosion protection methods of stainless steel mainly include cathodic protection,organic coating,metal coating,etc.the aluminum alloy coating is a common sacrificial anode coating,and its uniform and dense features can not only provide good physical shielding protection for the substrate,it can also provide cathodic protection for stainless steel substrates as a sacrificial anode.Conventional aluminum alloy coatings are often prepared by thermal spraying,the principle is to use a heat source to heat the raw materials for coating to the molten or semi-molten state.After exploration,the flames can be atomized by the power of the flame flow or an external high-speed air flow.Spray onto the surface of the substrate at a certain speed to form a coating.Cold spray technology is based on aerodynamics,uses high-pressure gas sources to accelerate solid particles to an extremely high velocity striking the substrate to form coating.Cold spraying technology compared with the traditional thermal spraying technology has a lower temperature during spraying,so can avoids oxidation,phase change,burning and other Adverse phenomena during the spraying process.In addition,cold spray technology has a smaller thermal effect on the substrate.In this paper,high-pressure cold spray technology was used to prepare cold-sprayed aluminum coatings on the surface of aluminum alloy and stainless steel respectively.The microstructure,and mechanical properties of the prepared cold-sprayed aluminum coatings were tested and analyzed using various modern materials characterization methods.The corrosion behavior of cold-sprayed aluminum coatings on two different substrates was analyzed using electrochemical test characterization methods.Neutral salt spray test was used to test the atmospheric corrosion behavior of two cold sprayed aluminum coatings.Two kinds of cold-sprayed aluminum coatings prepared using optimized process parameters were characterized by micro-morphology,it was found that uniform and dense cold-sprayed aluminum coating about 900 ?m thick was successfully prepared on the surfaces of aluminum alloys and stainless steels by cold spray technology respectively.Observation of the surface and cross-section of the coating showed that there were no pores or cracks in the coating that penetrated through the substrate,and the particles were fully deformed and bonded tightly.No oxide peak was found in both coatings by XRD analysis.The microhardness test of the two coatings showed that the micro-hardness of the cold-sprayed aluminum coating was slightly lower than that of the bulk aluminum alloy,but the whole is the same as the bulk metalThe open circuit potentials,polarization curves,and electrochemical impedances for cold-sprayed aluminum coatings on the two different substrates and the substrate materials in 3.5%wt.NaCl solution and acetic acid solution were tested and analyzed.The effects of acetic acid concentration and temperature on the corrosion behavior of cold sprayed aluminum coating and its substrate were discussed.The results show that in the 3.5%wt.NaC1 solution and acetic acid solution,the cold sprayed aluminum coating shows similar electrochemical characteristics to the substrate,indicating that the prepared cold spray coating has equivalent corrosion resistance to bulk aluminum alloy.In electrochemical tests with different concentrations of acetic acid,it can be found that corrosion does not only increase with increasing concentration,but there are special peak.Under the condition of 30%wt.and 90%wt.acetic acid solution concentration,the annual corrosion rate is an order of magnitude higher than that of 10%wt.and 50%wt.acetic acid concentration.The acetic acid concentration has a weak influence on the stainless steel matrix.The effect of acetic acid solution temperature on the corrosion behavior of the coating and the substrate was discussed.The results show that the corrosion current density of the coating increases with increasing temperature,and the current density peaks at 70?.With the increase of temperature,the passivation zone of the stainless steel disappears in the polarization curve,and the passivation capability is lost.When the temperature rises to 100?,the corrosion current density increases by two orders of magnitude compared to 25?.At this time,the stainless steel substrate is considered to be This environment is basically not resistant to corrosion,and the acetic acid temperature has a drastic effect on the corrosion of stainless steel substrates.In order to study the long-term protection ability of the cold spray coating on the substrate,a 90-day immersion test was performed in a 3.5%wt.NaCI solution.The results showed that the cold sprayed aluminum coating can provide long-term effective barrier protection for the substrate.The long-term immersion experiment in 90%wt.acetic acid solution showed that the corrosion resistance of the sample dropped rapidly with the increase of the immersion time,and the corrosion was severe after 7 days of immersion.The cold sprayed aluminum coating and A11050 are not suitable for service under high acetic acid concentration.1000 hours neutral salt spray test was used to test atmosphere corrosion behavior of coating.The results showed that the cold sprayed aluminum coating undergoing a 1000-hour neutral salt spray test did not appear the defects such as breakage and cracks that penetrate the coating to reach the substrate still maintain good protection performance,which indicates that the coating can provide excellent corrosion protection under atmospheric corrosion conditions.The galvanic corrosion behavior of cold-sprayed aluminum coating and substrate in 3.5%wt.NaCI and 90%wt.acetic acid solution was investigated.The different solutions,different solution flow rates,and different coatings-substrate exposed area ratios were investigated.The results show that the galvanic corrosion of the cold-sprayed aluminum coating and the aluminum alloy substrate couple is extremely sensitive to the change of the flow rate of the solution,means the flow rate of the solution is increased,and the current density of the galvanic couple rapidly increases.