In-vitro corrosion performance of hydroxyapatite-coated Al2024 in simulated body fluid: A comparative study

In this study, the applicability of hydroxyapatite (HA) coatings on Al-Cu-Mg alloys (Al2024) was investigated by electrochemical techniques. The structural characterizations of the coated layers were investigated by SEM, EDS, and XRD equipment. The surface adhesion resistance and electrochemical degradation behavior were tested by scratch and potentiodynamic scanning (PDS) tests, respectively. It was observed that the HA coating had a homogeneous structure on the Al2024 surfaces, but some local areas could not be adequately coated with HA from the cross-section images. Also, the coating surfaces were microporous morphology, which is specific to the HA coatings. From the scratch test results of the coating, it was predicted that the critical load resistance (Lc1), 12N, would be sufficient for biomedical applications. Electrochemical corrosion tests revealed that HA coating decreased the corrosion current density (Icorr) and corrosion rate of the Al2024 alloy (0.885 and 5.260 µA·cm-2 for HA-coated and uncoated Al2024 alloy, respectively). However, despite the low Icorr value obtained with HA coating, it was observed that both Icorr and passivation current density (Ipass) values (3.15 µA·cm-2 for HA coating, 0.03 to 0.08 µA·cm-2 for different types of titanium alloys) were insufficient when compared to commercial titanium alloys.