Micro and sub-micron surface structuring of AZ31 by laser re-melting and dimpling

• Surface roughness was controlled between Ra=0.22 μm and 4.50 μm.
• Nano fibrous surfaces were obtained with re-melting above Fl=500 J/cm2.
• Sub-micrometric feature growth was linked to MgO generation kinetics.
• Gentle and strong ablation regimes in dimpling identified at F0=10 J/cm2.
• Surface structures did not deteriorate mechanical properties.

In this work, the use of ns-pulsed fibre laser for surface structuring of AZ31 Mg alloy is investigated. Surface re-melting was employed to change surface morphology, especially in terms of surface roughness. Dimpling by percussion microdrilling was investigated to control the hole geometry.. With surface remelting mono-directional and homogeneous surfaces were obtained with Fl<500 J/cm2. Above 500 J/cm2 particle generation was observed, which induced sub-micron structure growth with nano-fibrous features. Moreover, surface roughness could be controlled below the initial value and much higher. With dimpling, transformation from gentle to strong ablation was observed at F0=10.3 J/cm2. XRD analysis was employed to link oxide growth to the surface morphology. Tensile tests were carried out to assess the damage on the mechanical properties after surface structuring.