Surface treatments for the improvement of mechanical and cavitation resistance of Al 6082 alloy

Nowadays, naval propellers are made in Ni-Al or Mn-Al bronzes, which are affected by high cavitation erosion. In this study, the possibility of adopting 6xxx alloy with different superficial treatments obtained through fluidised beds and laser surface texturing was investigated. 6xxx alloy series is known for its versatility due to an excellent mix of mechanical and physical properties, combined with ease of processing, welding, and good chemical resistance; however, its main drawback is low resistance to cavitation erosion. In this study, a total of 4 different surface treatments were produced and characterized such as fluidised bed coatings (Al2O3, S280) and laser textured samples (0-30% overlap). Moreover, the effect of a heat-treatment was evaluated for each kind of specimen analysed. The study was divided into two steps: in the first phase, the samples were morphologically and mechanically characterised through roughness measurements, micro-hardness, scratch, wear, and wettability tests. Successively, a modified ASTM-G32-10 standard was adopted to assess the cavitation erosion resistance; in particular, for each sample, mass and volume loss were analysed and compared to the as-built sample. Results showed a drastic reduction of the wear evaluated through pin-on-disk tests with the application of the high hardness coatings (Al2O3, S280) while a reduction of the cavitation erosion volume of about 20% lower was obtained through the best laser texturing treatment.