Corrosion behaviour of laser surface melted magnesium alloy AZ91D

•Corrosion behavior of AZ91D Mg alloys is intimately related with its microstructure.•Laser surface melting treatments allows surface modification of the microstructure.•Different laser parameters can achieve different microstructures.•Controlling laser parameters can produce different corrosion rates and morphologies.•Increase of surface roughness due to laser treatment is relevant to the corrosion rate.

A high power diode laser (HPDL) was used to produce laser surface melting (LSM) treatments on the surface of the Mg alloy AZ91D. Different treatments with different microstructures were produced by varying the laser-beam power and laser-scanning speed. Corrosion evaluation, using hydrogen evolution and electrochemical measurements, led to a relationship between microstructure and corrosion. Most corrosion rates for LSM treated specimens were within the scatter of the as-received AZ91D, whereas some treatments gave higher corrosion rates and some of the samples had corrosion rates lower than the average of the corrosion rate for AZ91D. There were differences in corroded surface morphology. Nevertheless laser treatments introduced surface discontinuities, which masked the effect of the microstructure. Removing these surface defects decreased the corrosion rate for the laser-treated samples.