Microstructure and surface texture driven improvement in in-vitro response of laser surface processed AZ31B magnesium alloy

The present work explored effects of laser surface melting on microstructure and surface topography evolution in AZ31B magnesium alloy. Thermokinetic effects experienced by the material during laser surface melting were simulated using a multiphysics finite element model. Microstructure and phase evolution were examined using scanning electron microscopy, X-ray diffraction, and electron back scatter diffraction. Surface topography was evaluated using white light interferometry. The interaction of surface melted samples with simulated body fluid was monitored by contact angle measurements and immersion studies up to 7 days. Laser surface melting led to formation of a refined microstructure with predominantly basal crystallographic texture. Concurrently, the amount of β phase (Mg17Al12) increased with an increase in the laser fluence. β phase preferentially decorated the cell boundaries. In terms of topography, the surface became progressively rougher with an increase in laser fluence. As a result, upon immersion in simulated body fluid, the laser surface melted samples showed an improved wettability, corrosion resistance, and precipitation of mineral having composition closer to the hydroxyapatite bone mineral compared to the untreated sample.