Influence of High Rotational Speeds on the Microstructure and Properties of Friction Stir Manufactured ZK61 Magnesium Alloy-Hydroxyapatite Composites

Friction stir processing (FSP) with high rotational speeds was successfully adopted to fabricate nano-hydroxyapatite (nHA)-reinforced ZK61 magnesium matrix composites (MMCs). And the influence of high rotational speeds on ZK61-nHA composites manufactured by FSP was investigated. The microstructure studies indicated that a higher rotational speed for FSP contributed to the formation of grain refinement and the uniform distribution of nHA particles. The average grain size was refined from 150 to 2.8 and 2.2 mu m at the stirred zones of FSP ZK61 and ZK61-nHA composites, respectively. And the uniformity and average values of microhardness were also positively correlated with the increase in rotational speeds. Moreover, corrosion tests revealed that samples prepared at 5000 rpm obviously had better corrosion resistance (E-corr = -1.484 V and I-corr = 1.536 x 10(-5) A/cm(2)), which greatly improved the relative growth rate (RGR) of ZK61-nHA samples to 81.60% in the CCK-8 cell viability assay.