Effect of Laser Surface Treatment on the Distribution of Beta Phase and Intermetallic Particles and the Surface Integrity of AA5456 Alloy

Abstract AA5456-H116 alloy is widely used in marine environments owing to the combination of mechanical properties and general corrosion resistance. However, precipitation of β phase (Al 3 Mg 2 ) on grain boundaries can occur at modestly elevated temperatures (> 50 °C), resulting in susceptibility to intergranular corrosion (IGC), intergranular stress corrosion cracking (IGSCC), and corrosion fatigue. This work uses electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) to examine the effect of continuous wave (CW) and defocused continuous wave (DCW) fiber laser surface treatment (LST) on the β phase and constituent intermetallic particles distribution in AA5456. The surface topography and subsurface defect distribution in the LST regions are also investigated; the presence of cracks and porosity was observed. Different CW/DCW processing parameters result in different aspect ratios, subsurface defects, and microstructures; specifically, surface polishing revealed the presence of subsurface defects up to 300 µm in size for CW conditions. Statistical analysis of the constituent particles distribution revealed a reduction in the total volume and size distribution in the LST region. Linear β coverage analysis along grain boundaries in the laser-treated region demonstrated that both CW and DCW LST processes are capable of resolutionizing β particles. Although both CW and DCW LSTs are equally effective in resolutionizing the β particles, DCW outperformed CW in terms of minimizing subsurface defects along with the formation of uniform melt pool distribution.