Enhancing Corrosion Resistance and Antibacterial Properties of ZK60 Magnesium Alloy Using Micro-Arc Oxidation Coating Containing Nano-Zinc Oxide

doi:10.1007/s40195-024-01770-5

Abstract

Abstract:

Nano-zinc oxides (ZnO) demonstrate remarkable antibacterial properties. To further enhance the corrosion resistance and antibacterial efficiency of magnesium alloy micro-arc oxidation (MAO) coatings, this study investigates the preparation of ZnO-containing micro-arc oxidation coatings with dual functionality by incorporating nano-ZnO into MAO electrolyte. The influence of varying ZnO concentrations on the microstructure, corrosion resistance, and antibacterial properties of the coating was examined through microstructure analysis, immersion tests, electrochemical experiments, and antibacterial assays. The findings revealed that the addition of nano-ZnO significantly enhanced the corrosion resistance of the MAO-coated alloy. Specifically, when the ZnO concentration in the electrolyte was 5 g/L, the corrosion rate was more than ten times lower compared to the MAO coatings without ZnO. Moreover, the antibacterial efficacy of ZnO + MAO coating, prepared with a ZnO concentration of 5 g/L, surpassed 95% after 24 h of co-culturing with Staphylococcus aureus (S. aureus). The nano-ZnO + MAO-coated alloy exhibited exceptional degradation resistance, corrosion resistance, and antibacterial effectiveness.

Key words: Nano-ZnO, Micro-arc oxidation (MAO) coating, ZK60 alloy, Corrosion behavior, Antibacterial characteristics

Jin-Xiu Li, Jun-Xiu Chen, M. A. Siddiqui, S. K. Kolawole, Yang Yang, Ying Shen, Jian-Ping Yang, Jian-Hua Wang, Xu-Ping Su. Enhancing Corrosion Resistance and Antibacterial Properties of ZK60 Magnesium Alloy Using Micro-Arc Oxidation Coating Containing Nano-Zinc Oxide[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(1): 45-58.

Figures/Tables 19

Table 1 Composition of the electrolyte (g/L)

Samples	KOH	Na₂SiO₃·9H₂O	KF·2H₂O	Nano-ZnO
MAO	1	10	8	-
ZnO + MAO	1	10	8	2/5/8

Table 2 Composition of the Hank's solution (g/L)

Composition	NaCl	KCl	KH₂PO₄	MgSO₄·7H₂O	NaHCO₃	CaCl₂	Na₂HPO₄	C₆H₁₂O₆
Content	8.00	0.40	0.06	0.20	0.35	0.14	0.13	1.00

Fig. 1 Microscopic morphologies of coating cross section: a Z0; b Z2; c Z5; d Z8

Fig. 2 Microscopic morphologies of coating surface: a Z0; b Z2; c Z5; d Z8

Fig. 3 BSE images: a Z5; b1 and b2 Z8

Table 3 EDS results for areas marked as A, B, C, and D in each coating

Samples	Elemental composition (at.%)
Samples	O	F	Mg	Si	Zn
Z0	48.5	8.2	31.7	11.0	0.7
Z2	50.8	6.3	32.2	9.7	0.9
Z5	46.8	9.2	30.9	9.7	3.5
Z8	49.6	8.3	31.5	9.4	1.2

Fig. 4 XRD patterns of coatings: a Z0; b Z2; c Z5; d Z8

Fig. 5 Polarization curve of the sample in Hank's solution

Table 4 Fitting results of dynamic polarization curves of samples in Hank's solution

Samples	i_corr (μA/cm²)	E_corr (V vs. SCE)	Corrosion rate (mm/y)
Z0	0.76 ± 0.3	− 1.45 ± 0.01	0.0174 ± 0.001
Z2	0.08 ± 0.002	− 1.48 ± 0.02	0.0018 ± 0.0001
Z5	0.06 ± 0.002	− 1.49 ± 0.01	0.0002 ± 0.00001
Z8	0.29 ± 0.01	− 1.49 ± 0.02	0.0066 ± 0.0001

Fig. 6 Electrochemical tests of impedance curves: a Nyquist curves; b Bode curves; c Bode phase angle curves; d equivalent circuit of ZnO + MAO coated alloy

Fig. 7 Changes in pH value of the solution during the immersing process of the sample

Table 5 Fitting results of the impedance curve of the sample in Hank's solution

Samples			Z0	Z2	Z5	Z8
R_s		(Ω cm²)	8.45 × 10^-5	17.85	16.84	23.56
Q₁	Y₀₁	(S sⁿ cm⁻²)	1.84 × 10^-6	2.88 × 10^-7	2.56 × 10^-7	1.68 × 10^-7
Q₁	n₁		0.60	0.81	0.81	0.84
R₁		(Ω cm²)	3.20 × 10³	3.94 × 10³	4.10 × 10³	2.41 × 10³
Q₂	Y₀₂	(S sⁿ cm⁻²)	3.65 × 10^-6	1.42 × 10^-6	1.8510^-6	2.03 × 10^-6
Q₂	n₂		0.56	0.65	0.63	0.62
R₂			3.946 × 10⁴	6.44 × 10⁴	6.49 × 10⁵	6.11 × 10⁴
L		(H cm⁻²)	2.34 × 10⁴	2.38 × 10⁴	2.32 × 10⁷	2.49 × 10⁴
R₃		(Ω cm²)	1.99 × 10⁴	1.30 × 10⁴	1.39 × 10⁵	1.68 × 10⁴

Fig. 8 Surface morphologies of the coating after 7 days of immersion: a1 Z0; b1 Z2; c1 Z5; d1 Z8. Surface morphologies after immersing for 14 days: a2 Z0; b2 Z2; c2 Z5; d2 Z8. Surface morphologies of the corrosion products were removed after 14 days of immersion: a3 Z0; b3 Z2; c3 Z5; d3 Z8. Macro-morphologies of coating surface after 14 days of immersion: a4 Z0; b4 Z2; c4 Z5; d4 Z8

Fig. 9 Cross-sectional morphologies of the coating after being immersed for 7 days: a1 Z0; b1 Z2; c1 Z5; d1 Z8; cross-sectional morphologies after immersing for 14 days: a2 Z0; b2 Z2; c2 Z5; d2 Z8

Fig. 10 XRD pattern after immersing for 14 days

Table 6 EDS results of corroded surfaces of coated samples after immersion

Samples	Immersion days	Elemental composition (at.%)
Samples	Immersion days	O	Mg	Si	P	Ca	Zn
Z0	7	61.6	22.9	6.3	5.5	3.4	0.5
Z0	14	55.0	25.7	8.6	5.4	4.0	1.3
Z2	7	57.3	27.2	7.4	4.1	2.7	1.3
Z2	14	54.4	27.4	7.7	5.7	3.6	1.1
Z5	7	59.7	27.4	7.4	2.6	1.3	1.6
Z5	14	53.5	27.0	8.3	5.9	4.0	1.3
Z8	7	62.6	22.6	5.1	4.4	3.8	1.6
Z8	14	53.8	28.5	8.0	4.7	3.1	1.9

Fig. 11 Antibacterial effects of co-culturing blank group, uncoated sample, coated sample with Staphylococcus aureus for 6, 12, and 24 h

Fig. 12 a Concentration of Staphylococcus aureus in antibacterial solution; b antibacterial rates of different samples against Staphylococcus aureus

Fig. 13 Schematic diagram of corrosion mechanism, a and c MAO coating without ZnO. There are many micro-pores that act as the corrosion channel, and the substrate is easily corroded. b When ZnO is introduced into the coating, the micro-pores sites are occupied by the ZnO. Moreover, it is beneficial for the formation of compact inner layer. d When the coating is corroded, some ions such as Mg2+, PO43−, OH−, cannot permeate into the substrate. They deposit on the surface of the coating and increase the corrosion resistance

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