Experimental Study On Laser Cladding Of Copper-base And Nickel-base Corrosion Resistant Alloy Coatings On Aluminum Alloy Surface

Corrosion is one of the major factors that restrict the broad application of aluminium alloy in the Marine environment.and the traditional surface modification technology has been challenging to meet the needs of modern corrosion protection.With the advantages of high bonding strength,wide application of materials,energy saving and environmental protection,laser cladding technology has entered the public eye.In order to improve the corrosion resistance of aluminum alloy and study the bonding mechanism of aluminum alloy and cladding layer,the Cu-xNi(x=15\25\35\45 wt.%)alloy cladding layer and Cu-xNi/NiCrMo composite cladding layer were prepared on the surface of 5083 aluminum alloy by laser cladding technology.In this paper,the morphology and phase composition of cladding layer,interface microstructure and composition distribution were studied,and a series of performance tests were carried out.At the same time,the influence of Ni content on the bonding properties and corrosion resistance of the cladding layer was studied.The results show that the cladding layers of the two alloys have dense microstructure and no defects such as cracks and pores.The cladding layer of Cu-xNi alloy consist of CuNi matrix and AlNi3 dendrite.The morphology of cladding layer changes with the increase of diffusion distance.At the bottom of the cladding layer,the content of Al element is higher,and the cladding layer is composed of a large number of coarse grey boughs(AINi3)and white matrix(CuNi).The gray branch structure(AlNi3)in the center of the cladding layer is fine and evenly distributed on the white matrix in a grid shape.On the surface of the cladding layer,the gray structure is greatly reduced,and the gray ball is dispersed in the white matrix.The cladding layer of NiCrMo alloy are composed of γ-Ni solid solution,and the morphology of the cladding layer is equiaxed and Mo-rich meshed intergranular structure.The bonding interface between Cu-xNi alloy cladding layer and Al matrix is composed of off-white intermetallic compound and black α-Al matrix.With the increase of Ni content,the size of the gray and white intermetallic compounds became coarse,the roughness of the binding interface decreased,and the defects increased.Microcomponent detection and surface scanning show that Ni elements in the cladding layer of Cu-xNi alloy increase,and the more Ni passes through the bonding interface,the coarser the intermetallic compounds generated with Al.In the polarization curve test and impedance test of electrochemical performance,the two kinds of alloy cladding showed excellent corrosion resistance.Cu-xNi/NiCrMo alloy cladding not only greatly reduce the corrosion tendency,but also greatly reduce the corrosion rate after the occurrence of corrosion.The electrochemical performance test results were verified by salt spray experiment.The surface of Al has been partially exfoliated,and the corrosion product is the mixture of Al3Cl and Al2O3.The surface of CuxNi alloy cladding layer produced yellowish-green corrosion product film,which was detected as the mixture of Cu2O and Cu2(OH)3Cl.Cu-xNi/NiCrMo composite cladding layer has a high surface finish,no obvious corrosion traces,and the surface is Cr2O3+NiO protective film.In the hardness test,the surface hardness of NiCrMo alloy cladding layer is much greater than that of Al alloy substrate because of the effect of solid solution strengthening.In the shear experiment,the shear strength of Cu-xNi alloy cladding and Cu-xNi/NiCrMo composite cladding are high.The shear strength decreases with the increase of Ni content.There are cleavage planes and a lot of dimples in the fracture,which is judged to be a mixed fracture mode,which further confirms the bonding mechanism of the brittle phase at the α-Al coating interface between the alloy cladding layer and the matrix.In conclusion,Cu-xNi alloy cladding layer and Cu-xNi/NiCrMo cladding layer prepared by laser cladding process on aluminum alloy surface can protect aluminum matrix well.Among them,Cu15Ni/NiCrMo and Cu25Ni/NiCrMo cladding can greatly improve the surface properties of aluminum alloy while maintaining excellent bonding properties,so they have broad application prospects.