Surface oxidation by laser soft-melting treatment to change degradation behaviour of a magnesium alloy

The use of Mg and its alloys has been limited in engineering applications due to their low corrosion resistance. On the other hand, since a tuned degradation rate is attractive for biomedical applications, Mg and related alloys are considered a promising choice as bioresorbable metals. However, biomedical applications require a greater control of degradation behaviour and rate. Presence of O2 and atmospheric moisture (H2O) strictly affect degradation behaviour of magnesium alloys whose corrosion is accelerated in humid environment. Several authors studied the effect on Mg corrosion of different surface modification methods and environmental parameters. In this work, a laser treatment of an AZ31 Mg alloy is proposed as a surface treatment using a soft-melting approach. A ns pulsed fiber laser operating was used to promote different stages of surface oxidation, under two process conditions at different energy density applied in ambient atmosphere. Laser treatment directly generated a morphology change and a chemical modification of Mg substrates. Laser soft-melted surfaces at different conditions were tested and the laser effect on degradation behaviour of AZ31 was evaluated. Roughness measurement with an optical profilometer, surface morphology investigation using SEM analysis and chemistry evaluation by XPS technique were carried out. The relationship between laser action and changes in degradation behaviour of AZ31 Mg alloy was investigated. The studied conditions were compared to the untreated cold-rolled surface as reference.