Corrosion Studies of Laser-melted Aluminium Alloys

The corrosion behaviour of laser-melted AA 2014-T6 and AA 2024-T351 alloys has been investigated to enhance the knowledge of important, but poorly understood, relationships between corrosion and microstructural characteristics of surfaces following laser treatment. Examination of laser-melted surfaces in terms of microstructure and phase analysis was performed using scanning electron microscopy (SEM), with associated elemental analysis by energy dispersive X-ray (EDX) spectroscopy, electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Pitting corrosion resistance was evaluated using potentiodynamic anodic polarisation in 1 M NaCl solution. The work revealed that there was an improvement of pitting corrosion resistance for the laser-melted AA 2014-T6 alloy, but no improvement for AA 2024-T351 alloy, indicating that the refinement of the microstructure, per se, with finer intermetallic particles, did not dominate corrosion performance. More importantly, the electrochemical characteristics of the second–phase particles with respect to the -Al matrix and the extension of copper solubility in the -Al matrix, leading to an increased corrosion potential, were considered to be the key factors responsible for the corrosion behaviors of the laser-melted alloys. In addition, cooling rate, microsegregation along grain boundaries, and heat-affected zones produced by overlapping also play important roles in corrosion behaviour after laser treatment.