Nucleation and strengthening mechanism of laser cladding aluminum alloy by Ni-Cr-B-Si alloy powder based on rare earth control

Abstract

To improve the comprehensive performance of aluminum alloy and expand its application range, a laser cladding technology was used to a prepare Ni-Cr-B-Si alloy cladding layer, adding 4% CeO 2 , 5% Y 2 O 3 , and 5% La 2 O 3 on the surface of 6063Al. The distribution of elements, the nucleation and growth mechanism of the interface transition and upper cladding layers, and the action mechanism of rare earths were analyzed from the thermodynamics, kinetics, and solidification perspectives. Results show that the cladding layer is mainly composed of a thin interface transition layer at the bottom and a thick cladding layer at the top. There are numerous pores and cracks in the interface transition layer of the Ni-Cr-B-Si cladding layer, part of the cladding layer is peeled off, and the structure is obviously segregated. However, the cladding layer adding with 4% CeO 2 , 5% Y 2 O 3 and 5% La 2 O 3 has no obvious pores, cracks and shedding, its grain distribution is more dispersed, and the structure is refined. The organization state from good to poor follows the order Ni60 + 4%CeO 2 cladding layer, Ni60 + 5%Y 2 O 3 cladding layer, and Ni60 + 5%La 2 O 3 cladding layer. It was found through research that the addition of rare earth can improve the fluidity of the molten pool during the solidification of the cladding layer and purify the molten pool, and most of the rare earths are segregated at the grain boundary and phase boundary, which strengthens the grain boundary and phase boundary. The strengthening mechanism of the cladding layer is solid solution strengthening and fine grain strengthening, and the Ni60 + 4% CeO 2 cladding layer also has a strengthening mechanism of dispersion strengthening.