LASER CLADDING ON ALUMINUM-BASE ALLOYS - MICROSTRUCTURAL FEATURES

There is great interest in using high power lasers for surface alloyin g or cladding on aluminium alloys, in order to enhance hardness and to improve wear resistance. This study reports microstructural investiga tions 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 A l-Si-based cast alloy. In the second stage, hard particles were also a dded to the powder, in order to increase the elastic modulus of the cl adding; either oxides or carbides were used, but the best solution app eared to be the injection of TiC, which has a very high Young's modulu s. After the optimization of the laser-processing parameters, sound cl addings were obtained. Their main features are as follows: thickness, up to 1 mm, in a single pass; soundness, no pores or cracks; microstru cture, 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 dis tributed); the Vickers hardness, up to 800 HV, when carbides particles are present; thermal stability, no evolution during thermal cycling b ecause of the existence of stable phases and only limited coalescence of the formed dendrites.