LASER CLADDING ON ALUMINUM-BASE ALLOYS - MICROSTRUCTURAL FEATURES

There is great interest in using high power lasers for surface alloying or cladding on aluminium alloys, in order to enhance hardness and to improve wear resistance. This study reports microstructural investigations and the correlation with the hardening phenomenon. In the first stage, a mixture of Al-Si and Ni powders was used for cladding on an Al-Si-based cast alloy. In the second stage, hard particles were also added to the powder, in order to increase the elastic modulus of the cladding; either oxides or carbides were used, but the best solution appeared to be the injection of TiC, which has a very high Young's modulus. After the optimization of the laser-processing parameters, sound claddings were obtained. Their main features are as follows: thickness, up to 1 mm, in a single pass; soundness, no pores or cracks; microstructure, dendritic energy-dispersive spectroscopy and X-ray experiments reveal the Al3Ni and Al3Ni2 phases in the dendrites, and mainly Al and Si in the interdendritic areas; when TiC particles are also injected, they are found to be unaffected in the surface layer and randomly distributed); the Vickers hardness, up to 800 HV, when carbides particles are present; thermal stability, no evolution during thermal cycling because of the existence of stable phases and only limited coalescence of the formed dendrites.