Microstructure And Properties Of NiCu-based Coatings On Magnesium Lithium Alloys By Cold Spraying / Laser Alloying

As one of the lightest alloy materials at present,Magnesium lithium（Mg-Li）alloy has a broad application prospect in aerospace,automobile,3C digital and other lightweight fields.However,the low hardness,poor wear-resistance and corrosion-resistance significantly limit the application of Mg-Li alloy.In this work,aluminum bronze coatings were prepared on Mg-Li alloy by cold spraying technology.After that,laser surface alloying was carried out on the cold spraying coatings,and Ni,Cr,Fe and other alloying elements were introduced to prepare NiCu based gradient coatings.In order to further improve the coating performance,laser surface alloyed NiCu-xTi gradient coatings with different Ti additions were prepared on the cold-sprayed aluminum bronze coatings.The microstructure,microhardness,wear-resistance and corrosion-resistance of the coatings were studied.The research results are listed as follows:1.The eutectoid transformation ofβ→α+γ₂ and grain refinement occurred during cold spraying process.The average microhardness of the cold-sprayed aluminum bronze coating was about 4.5 times that of Mg-Li alloy.The wear loss of the coating was about 47.5%that of Mg-Li alloy.2.After laser surface alloying,NiCu-based gradient coatings were prepared.At the interface region between the coating and the substrate,metallurgical reaction took place and heat affected zone formed.The alloyed layer was mainly composed of Ni-rich and Cu-rich solid solution phases,and the microstructure was uniform and dense.The wear resistance of the coatings was improved by laser surface alloying.Compared with the cold-sprayed aluminum bronze coating,the alloyed coating had better wear resistance and corrosion resistance.After laser surface alloying,the wear loss and the corrosion current density of the coatings were reduced by 21%and two orders of magnitude respectively,compared with that of cold-sprayed aluminum bronze coating.3.The laser surface alloyed NiCu-xTi coatings with different Ti additions had different microstructures.A large number of dispersed second phases and fine precipitated phases formed in the coatings.Moreover,with the increase of Ti addition,the microstructures of the coatings were refined with different degrees.When Ti element with a mass fraction of 40%was added,the microstructure refinement was the most obvious.4.The microhardness and wear resistance of laser surface alloyed NiCu-xTi coatings increased with the increase of Ti additive amount.The average microhardness of the NiCu-40Ti coating was about 2 times that of the coating without Ti addition and about 11 times that of the substrate.The wear loss of NiCu-40Ti coating was only 7.5%of that before Ti addition,with a reduction of up to 92.5%.The laser surface alloyed NiCu-xTi coatings showed good corrosion resistance.The NiCu-20Ti coating had the highest corrosion potential and low corrosion current density.The NiCu-40Ti coating had a stable passivation film.