In order to improve the corrosion resistance and bioactivity of biodegradable Mg alloy substrate, novel Zn-HA/
Zn double-layer coatings with different HA/Zn ratios in weight were deposited on AZ91D substrates by cold
spraying. Phase compositions and microstructures of as-sprayed coatings and coatings after corrosion tests were
analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron
microscopy (SEM). Electrochemical corrosion behaviors of both Zn-HA/Zn double-layer coatings were investigated
in Hanks’ simulated body fluid using potentiodynamic polarization and electrochemical impedance
spectroscopy (EIS). Results showed that both the pure Zn coating and HA/Zn composite coatings presented the
similar phase compositions with their primary powders in addition to Zn oxidizations. Zn powders were plastically
deformed and partially oxidized due to its low melting point, while HA powders were mainly crashed into
fragments and hill-like splats. Both Zn under layer and HA/Zn upper layer were well bonded and presented dense
structures, differences in HA/Zn upper layers were related to the HA/Zn ratios. Potentiodynamic polarization
and EIS measurements illustrated that the cold-sprayed Zn-HA/Zn double-layer coatings not only improve the
corrosion resistance of Mg alloy substrates, but also enhance its bioactivity due to the HA existed in composite
upper layer.

HA/Zn; Cold spraying;,Corrosion resistance