In-vitro bio-corrosion behavior of friction stir additively manufactured AZ31B magnesium alloy-hydroxyapatite composites.

Magnesium and its alloys have been considered for consumable bio-implant applications due to their similar mechanical properties to the natural bone and biodegradability. Nevertheless, uncontrollable corrosion rate and limited bioactivity of Mg based materials in biological environment restrain their application. In light of this, objective of the present study was to explore addition of hydroxyapatite (HA, Ca(PO)OH), a ceramic similar to bone mineral, into AZ31B Mg alloy and its effects on bio-corrosion behavior. Friction stir processing based additive manufacturing route was employed for producing AZ31B Mg-HA composites. Various HA contents (5, 10, and 20 wt%) were incorporated into Mg matrix. The microstructural observation revealed that the size of α-Mg grains reduced significantly after friction stir process. HA incorporation took place at micro/nanoscale in α-Mg matrix under the thermo-mechanical forces exerted by friction stir process. The corrosion behavior of friction stir processed Mg-HA composites was investigated using electrochemical methods in simulated body fluid. The results indicated an improvement in corrosion resistance for the composites compared to untreated AZ31B which was attributed to significant grain refinement upon friction stir process. On the other hand, incremental addition of HA had an opposing effect due to localized micro/nano-galvanic couples. As a result, friction stir process Mg-5 wt% HA composite demonstrated the highest corrosion resistance due to an optimum balance between beneficial effects of grain size refinement and limited number of local galvanic couples compared to the other friction stir process samples explored in the present work.