Manufacture of biodegradable magnesium alloy by high speed friction stir processing

Friction stir processing (FSP) with a high rotational speed (6000 rpm) was employed to modify surface properties of magnesium alloy through grain refinement and incorporated nano-hydroxyapatite (nHA) particles. Hardness testing indicated that the distributed nanoparticles have largely influenced the hardness of the surface layer and measurements of average hardness varied with different amounts of nHA particles applied. Corrosion tests revealed that FSP had reduced the corrosion rate of ZK60 magnesium alloy by more than one order of magnitude due to the combined effects of grain refinement and low surface energy. The corrosion rates of modified layers could be manipulated by nHA content of selection since nHA plays an important role in destroying the continuity of magnesium matrix and producing a more protective biomineralized film on composites when immersed in simulated body fluid (SBF). Two kinds of equivalent circuits were proposed to explain the corrosion mechanism. The simulation values fitted the experimental data very well by using the equivalent circuits, regardless of differences in samples.