Effect of Na<sub>2</sub>WO<sub>4</sub> Concentration on the Microstructure and Corrosion Behavior of Ni-W-P Ternary Alloy Coatings

Tian, Sha-sha; Sun, Wan-chang; Liu, Yu-wan; Jia, Ya-peng; Xiao, Yan

doi:10.1590/1980-5373-MR-2020-0580

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Articles • Mat. Res. 24 (4) • 2021 • https://doi.org/10.1590/1980-5373-MR-2020-0580 copy

Effect of Na₂WO₄ Concentration on the Microstructure and Corrosion Behavior of Ni-W-P Ternary Alloy Coatings

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Ni-W-P ternary coating was successfully deposited on AZ91D magnesium alloy by electroless plating with low energy consumption. The effect of Na₂WO₄ concentration on the microstructure, deposition rate, corrosion behavior, adhesion force, porosity test and micro-hardness of Ni-W-P ternary coatings were evaluated. Results reveal that when the concentration of Na₂WO₄ is 15 g/L in the plating solution, the coating with the average thickness of 17 μm is uniform and dense, and the content of phosphorus and tungsten reached 9.63 wt.% and 1.14 wt.% respectively, which presents amorphous structure. Meanwhile, when the concentration of Na₂WO₄ is 15 g/L, the amorphous Ni-W-P ternary coating has the best corrosion resistance, among which E_corr is -0.326 V, I_corr is 0.003 A/cm² in 3.5 wt.% NaCl solution. In addition, the mechanisms of corrosion resistance for the substrate and the coating were exploded.

Keywords:
Magnesium alloy; Ni-W-P ternary coating; Electroless; Microstructure; Corrosion behavior

Composition and operating parameters	Values
ZnSO₄·7H₂O	60 g/L
Na₂CO₃	140 g/L
KF	3 g/L
PH	9~9.5
Temperature	71°C
Plating time	17 min
Stirring rate	100 r/min
Bath volume	0.5 L

Composition and operating parameters	Values
CuSO₄·5H₂O	50 g/L
KNaC₄H₄O₆·4H₂O	140 g/L
NaOH	40 g/L
PH	11
Temperature	Room temperature
Plating time	1 h
Stirring rate	100 r/min
Bath volume	0.5 L

Composition and operating parameters	Values
NiSO₄·6H₂O	30 g/L
Na₂WO₄	5~20 g/L
NaH₂PO₂	50 g/L
Na₃C₆H₅O₇·2H₂O	25 g/L
NH₄F	10 g/L
CN₂H₄S	0.5~1 mg/L
PH	7~7.4
Temperature	60°C
Plating time	1 h
Stirring rate	300 r/min
Bath volume	0.5 L

Sample	Ni (wt.%)	P (wt.%)	W (wt.%)
No. 1	89.50	9.89	0.61
No. 2	89.34	9.81	0.85
No. 3	89.23	9.63	1.14
No. 4	90.86	7.90	1.24

Sample	Na₂WO₄ concentration (g/L)	E_corr(V)	I_corr(A/cm²)
Ma alloy substrate	0	-1.710	23.188
No. 1	5	-0.410	0.254
No. 2	10	-0.344	0.012
No. 3	15	-0.326	0.003
No. 4	20	-0.334	0.057

Sample	Na₂WO₄ concentration (g/L)	R_s(Ω·cm²)	Y_0,dl(S^α·Ω^-1·cm^-2)	n	R_ct(Ω·cm²)	χ²/10^-3
Ma alloy substrate	0	16.62	2.54×10^-5	0.82	3.76×10²	1.3
No. 1	5	12.25	1.83×10^-5	0.93	1.24×10⁴	3.6
No. 2	10	12.21	1.41×10^-5	0.93	2.72×10⁴	2.3
No. 3	15	11.87	1.27×10^-5	0.92	3.51×10⁴	4.1
No. 4	20	11.93	2.48×10^-5	0.85	2.03×10⁴	3.2

Sample	Test 1, HV	Test 2, HV	Test 3, HV	Average HV/MPa
No. 1(5 g/L)	186.2	130.8	116.2	144.4
No. 2(10 g/L)	157.0	137.2	143.3	145.8
No. 3(15 g/L)	269	267.3	270.9	269.1
No. 4(20 g/L)	359.4	373.8	311.6	348.3

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Effect of Na2WO4 Concentration on the Microstructure and Corrosion Behavior of Ni-W-P Ternary Alloy Coatings

Abstract

Effect of Na₂WO₄ Concentration on the Microstructure and Corrosion Behavior of Ni-W-P Ternary Alloy Coatings