High Power Diode Laser (HPDL) surface treatments to improve the mechanical properties and the corrosion behaviour of Mg-Zn-Ca alloys for biodegradable implants

Abstract

Biodegradability, low density and mechanical properties close to those of the bone are some of the intrinsic properties of the Mg-Zn-Ca alloys that have attracted significant attention for developing biodegradable implants. However, rapid degradation constitutes the main disadvantage of these alloys. In this work, two different alloys, Mg-1Zn-1Ca and Mg-3Zn-0.4Ca, were laser surface treated using a HPDL to increase hardness and to improve the corrosion performance. Depending on the laser parameters, a complete laser surface melting (LSM) or a selective laser surface melting (SLSM) were reached. The microstructure, mechanical properties and corrosion behaviour were established and compared. Higher laser input energies led to larger treated zones and in these cases two different regions could be distinguished: the outer zone, where the LSM took place, presented a more refined microstructure with a greater dispersion of secondary phases; the following zone suffered SLSM, in it only the secondary phases were modified by the HPDL. Hardness was 24%–27% higher than that of the untreated samples. The HPDL also reduced the corrosion rate by 21% and 37% for the Mg-1Zn-1Ca alloy and the Mg-3Zn-0.4Ca alloy, respectively, after 336 h of immersion in Hanks' solution at 37 °C.