Microstructure of laser-clad Ni60 cladding layers added with different amounts of rare-earth oxides on 6063 Al alloys

Abstract

Ni60 cladding layers added with different amounts of rare-earth CeO2, Y2O3, and La2O3 were prepared on the surface of 6063 aluminum alloys through laser cladding. The effects of such cladding layers on the macroscopic morphology, section morphology, micro-hardness, phase composition, microstructure, and composition distribution of the laser clad Ni-based coating were investigated by performing metallographic microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and micro-hardness test. Cladding layers with the optimum rare-earth contents were 4% CeO2 + Ni60 cladding layer, 5% Y2O3 + Ni60 cladding layer, and 5% La2O3 +Ni60 cladding layer. The main phase composition of the cladding layers included β-NiAl (Cr), Al3Ni, AlNi3, and Al. The Ni60 cladding layers added with rare-earth oxides produced a chemical reaction that was involved in the cladding process to form stable rare-earth compounds. Ni60 cladding layers added with 4% CeO2, 5% Y2O3, and 5% La2O3 were preferable over those without rare-earth oxides, as the former displayed smoother micro-morphologies without obvious pores and cracks. The dendritic structures of the Ni60 cladding layers were coarse; moreover, many grain segregations that were accompanied by a large number of pores were observed in the local area. By contrast, the Ni60 cladding layers added with rare-earth oxides displayed compact dendritic structures, and the grains were obviously refined. The hardness of the cladding layers from the surface to the substrate was gradually decreased as the cladding layer depth increased. Compared with Ni60 cladding layer, the transitions of Ni, Al, Cr, and other elements in the Ni60 cladding layers added with different amounts of CeO2, Y2O3, and La2O3 were became more observable with increasing depth, and the dilution rate of the cladding layer was reduced.