Laser surface engineering for improving cavitation erosion and corrosion resistance of manganese nickel aluminium bronze

Laser surface melting (LSM) of Manganese Nickel Aluminium Bronze (Cu-Mn-Al-Ni-Fe) to improve cavitation erosion and corrosion resistance was performed using a 2-kW continuous wave (CW) Nd-YAG laser. A modified layer with a single β-phase structure and with highly refined and homogenized grains was obtained. Under favorable laser processing conditions (Power = 1 kW; Scanning velocity = 35 mm/s; Spot diameter = 2 mm) the microhardness was increased by 2 times and the cavitation erosion resistance in 3.5 wt% NaCl solution was increased by 5.8 times. This was even higher than that of Nickel Aluminium Bronze (NAB). For as-received MAB, the SEM micrographs of the surface taken at an early stage of the cavitation erosion and general corrosion tests revealed that the iron/manganese-rich κΙ phase and the α/κΙ interface were initiation sites of damage. On the other hand, attack was much milder in the laser melted samples and started at the triple junctions of the grain boundaries. The corrosion current density in 3.5 wt% NaCl was also improved after laser surface melting, with a reduction from 9.54 μA/cm2 to 4.26 μA/cm2. The corrosion potential also shifted in the noble direction by about 80 mV. It could be concluded that the improvement in both cavitation erosion and corrosion resistance was in particular attributable to homogenization and refinement of the microstructure.