Research On Laser Cladding Rare Earth + Nickel 60 Alloy Coatings On The Surface Of Aluminum Alloys

Aluminum and aluminum alloy is widely used in non-ferrous metal materials with many excellent physical properties, for example, high thermal conductivity, low density,low coefficient of thermal expansion, high specific strength and stiffness, good plasticity and toughness, it has applied into the people’s production and daily life and the areas of aerospace, automotive, high-speed rail, engine pistons, optical instruments, missile mosaic structure. But it has poor surface properties such as low hardness, plastic deformation easily, bad wear and corrosion resistance, etc. Ni-based alloy by using laser cladding can greatly improve the surface performance of aluminum, it can be applied to the surface strengthening process of the gear, turbine, bushings, engine block and other parts, which not only meets the requirements of the lightweight design, but also maintain a high hardness and wear resistance on the surface of Ni-based coatings. However, due to the different physical and chemical properties of the Ni-based and Al-based alloys, there are large numbers of unavoidable holes, cracks and other organizational defects. Rare earth elements have good effects on grain refinement, removing impurities, purified grain boundaries and improving metal tissues. So it can be applied in reducing organization defects on the Ni-Based alloy coatings in a certain extent and enhancing the application properties.Ni60 alloy coatings with different contends of rare-earth Oxide La2O3、Y2O3、Ce O2 were prepared on the surface of 6063 aluminum alloy by using laser cladding. Investigated the effects and mechanism of rare earth elements, and researched on the influence of different rare earth oxide on the macroscopic morphology, section morphology, hardness,phase structure, element distribution, microstructure, friction and wear properties, and corrosion resistance performance of Ni-based cladding layers at the surface of 6063 Al.Analyzed the formation mechanism of the cladding layers, microstructure, and obtained the better ratio of rare earth. The main conclusions are as follows:(1) In the macro-morphology of the cladding layers, a lot of "lumps" or "nodule-like" fused tissue and gas sputtering holes appearing in the Ni60 cladding layer without adding rare earth oxide, the macro-morphology of Ni60 cladding layer added La2O3, Y2O3, Ce O2 three kinds of rare earth oxides have different degrees of improvement. Among them, when adding the rare earth oxide contents below 3%~4%, the cladding layers still have surface defects such as holes, tissue loss and surface uneven. While adding 4%~10% of rare earth oxides, Ni60 cladding layers have flat surface, no sheddings, and have good surfacemorphology.(2) In the cross-sectional morphology of the cladding layers, the average thickness of the cladding layers are about 800μm~1000μm. When the rare earth oxides La2O3, Y2O3,Ce O2 added amount are less than 4%, with the increase of rare earth content, the pores,cracks and other defects of cladding layers are improved. But when the rare earth added more than 5%, the pores, cracks are increased in the cladding layers. When adding 4%~5%rare earth oxides, the Ni60 cladding layers can obtain better cross-sectional morphology with less pores, cracks and other defects.(3) In the hardness of the cladding layers, the surface hardness of Ni60 cladding layer without rare earth oxides is 1020 HV0.1, much higher than the hardness of 6063 Aluminum alloy matrix,which is 147.2HV0.1. Adding 5% ~10% of La2O3, Y2O3, Ce O2 can improve the Ni60 cladding layer surface hardness up to 1300HV0.1~1400HV0.1. At the bottom of the cladding layers, Ni60 cladding layer hardness value is 200HV0.1~400HV0.1, average of lower about 100HV0.1~400HV0.1 than Ni60 cladding added rare earth oxides.(4) The main phase structures of Ni-Based alloy cladding layers with different contends of rare earth La2O3 are β-Ni Al(Cr) and a small amount of Al3 Ni, Al Ni3, Al, etc.After adding rare earth, a little of rare earth compounds La2O3、Al4La was found in XRD diagrams, and Ni Al phase(100) crystallographic orientation peak almost disappeared,grain orientation towards(110),(200) and(211), and(110) crystallographic orientation peaks appeared different degrees of migration.(5) The main phase structures of Ni60 cladding layers with different contends of rare earth Y2O3 are β-Ni Al(Cr) and a small amount of Al3 Ni, Al Ni3, Al, etc; The diffraction peaks of rare earth compounds such as Y2O3, YAl3, Al Ni Y, Ni17Y2 are also founded.(6) The main phase structures of Ni60 cladding layers added Ce O2 are β-Ni Al(Cr),Al3 Ni, Al Ni3, etc; The cladding layer contains a rare earth compound Ce Ni5,Ce3Ni6Si2, at higher ratio Ce O2 content, there presence of the Ni B12 diffraction peak.(7) The elements distribution in the cladding layers show that: Compared with non-rare earth oxides added Ni60 cladding layer, Ni60 cladding layer with La2O3, Y2O3,Ce O2 have lower dilution rate, the composition such as Ni, Al, Cr have obvious transition with depth and no Cr element segregation, the surface content of Ni element from 34.62%to above 60% after adding rare earth oxides, the content of rare earth elements from more than 1.0% of the surface to the bottom gradually reduce.(8) In the microstructure of cladding layers, adding La2O3, Y2O3, Ce O2 can improve the Ni60 cladding layer microstructure, promote the grain refinement of cladding layer,reduce the micro pores. The cladding layers mainly composed of Ni Al-Cr eutectic structure,rare earth elements segregate at the grain boundary and form some stable rare earth compound such as Al4 La.(9) Under the same conditions of friction and wear, compared with Ni60 cladding layer, the wear surface collapse damage degree of Ni60 cladding layer added rare earth oxides have reduced, the depth and width of grinding cracks are greatly reduced, wear loss are reduced, the friction coefficients are lower and stable. Among them, the wear loss of Ni60 cladding layer not adding rare earth is 0.0974 mm3, adding 4%~10% of La2O3, Y2O3,Ce O2 make the cladding layers of wear volume loss respectively to 0.0016 mm3~0.0124mm3, 0.0128 mm3~0.0336 mm3 and 0.0031 mm3~0.0090 mm3. 5% La2O3+Ni60 cladding layer is 54.1 times as that of Ni60 cladding layer, 5% Y2O3+Ni60 cladding layer is 6.1times as that of Ni60 cladding layer, 4% Ce O2+Ni60 cladding layer is 31.4 times as that of Ni60 cladding layer.(10) In 1mol/L H2SO4 solution, the corrosion resistance of 5% La2O3+Ni60 cladding layer is 3.79 times as that of Ni60 cladding layer, and 5.09 times as that of 6063 Aluminum alloy. 5% Y2O3+Ni60 cladding layer is 4.07 times as that of Ni60 cladding layer, and 5.46 times as that of 6063 Aluminum alloy. 4% Ce O2+Ni60 cladding layer is 4.25 times as that of Ni60 cladding layer, and 5.71 times as that of 6063 Aluminum alloy.(11) In 3.5% Na Cl solution, the corrosion resistance of 5% La2O3+Ni60 cladding layer is 2.15 times as that of Ni60 cladding layer, and 2.30 times as that of 6063 Aluminum alloy. 5% Y2O3+Ni60 cladding layer is 4.3 times as that of Ni60 cladding layer, and 4.59 times as that of 6063 Aluminum alloy. 4% Ce O2+Ni60 cladding layer is 1.4 times as that of Ni60 cladding layer, and 1.49 times as that of 6063 Aluminum alloy.(12) In 1mol/L Na OH solution, the corrosion resistance of 5% La2O3+Ni60 cladding layer is 2.21 times as that of Ni60 cladding layer, and 4.88 times as that of 6063 Aluminum alloy. 5% Y2O3+Ni60 cladding layer is 2.3 times as that of Ni60 cladding layer, and 5.09 times as that of 6063 Aluminum alloy. 4% Ce O2+Ni60 cladding layer is 1.43 times as that of Ni60 cladding layer, and 3.17 times as that of 6063 Aluminum alloy.