Investigation on underwater wire-feed laser deposition of 5052 aluminum alloy

The underwater laser deposition layer with uniform forming on the 5052 aluminum alloy was successfully manufacturing by the underwater wire-feed laser deposition (UWLD) technology with a laser deposition (LD) gas-shielding nozzle. Process parameters including deposition speed and wire feed speed were optimized and laser propagation attenuation mechanism, the geometrical characteristics, microstructure and microhardness of deposited track in the in-air and underwater environment were investigated. Increasing deposition speed or reducing wire feed speed, the wetting between the base material and deposited metal improved and a high-quality UWLD layer without defects was obtained at 15 mm/s deposition speed and 1.2 m/min wire feed speed. For UWLD, the laser beam energy decreased owing to absorption and scattering of aerosol particles, causing differences in the geometric features to in-air wire-feed laser deposition (IWLD) and reducing the wettability and fluidity of the deposited metal on the substrate. In both IWLD and UWLD layers, the microstructure of the deposition region (DR) was equiaxial dendrites while the fusion region (FR) was composed of columnar dendrites. The columnar dendrites nucleated at the fusion line and grew along the reverse direction of the temperature gradient to the centerline of the melt pool while the underwater grains were more refined attributed to the greater cooling rate under water, indicating the increase of microhardness.