Corrosion Resistance of AZ91 Mg Alloy Modified by High-Current Pulsed Electron Beam

doi:10.1007/s40195-018-0798-1

Abstract

Abstract:

The high-current pulsed electron beam (HCPEB) treatment with current density 6 J/cm² was applied on AZ91 Mg alloy to improve its corrosion resistance. Results showed that the net-like Mg₁₇Al₁₂ disappeared on the surface of AZ91 Mg alloy after irradiation by HCPEB, which was instead of supersaturated Al element on the surface. Nevertheless, the application of HCPEB also led to the formation of crater-like and groove-like structures as well as micro-cracks on the surface of AZ91 Mg alloy. After HCPEB treatment by 3, 5 and 10 pulses, the AZ91 Mg alloy exhibited better corrosion resistance. However, the increasing amount of micro-cracks reduced the anti-corrosive properties of AZ91 Mg alloy as the pulse increased to 20 and 30.

Key words: High-current pulsed electron beam (HCPEB), Corrosion resistance, Electrochemical impedance spectroscopy(EIS), AZ91 Mg alloy, Microstructure

Peng-Peng Wu, Kun-Kun Deng, Kai-Bo Nie, Zhong-Zhong Zhang. Corrosion Resistance of AZ91 Mg Alloy Modified by High-Current Pulsed Electron Beam[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(2): 218-226.

Figures/Tables 13

Fig. 1 OM images of AZ91 Mg alloy: a untreated and treated by HCPEB at the pulse of b 3, c 5, d 10, e 20, f 30

Fig. 2 SEM micrographs of AZ91 Mg alloy treated by HCPEB at the pulse of a 3, b 5, c 10, d 30

Table 1 EDS results of points in Fig. 2b

Points	Elements (at.%)
Points	Mg	Al	Zn
A	61.1	38.5	0.4
B	76.3	23.1	0.6
C	84.3	15.0	0.7

Fig. 3 XRD patterns of the samples: a 2θ range from 20° to 80°, b 2θ range from 30° to 45°

Fig. 4 EDS-layered map of AZ91 Mg alloy: a, b untreated, c, d treated by HCPEB at the 5 pulses. b, d are the Al map of a, c, respectively

Fig. 5 Aluminum contents of α-Mg in AZ91 Mg alloy treated by HCPEB

Fig. 6 OM micrographs of cross-sectional morphology irradiated for a 5 pulses, b 30 pulses

Fig. 7 Polarization curves of the samples

Table 2 Details obtained from polarization tests and CR calculated by Eq. (1)

Pulses of HCPEB	E_corr (V vs. SCE)	i_corr (μA/cm²)	-b_c (mV/dec)	E_b (V vs. SCE)	E_b - E_corr (V)	C_R (mm/year)
Untreated	-1.540	72.7	260.33	-	-	2.12
3 pulses	-1.492	18.4	105.61	-1.240	0.252	0.42
5 pulses	-1.459	15.1	101.29	-1.248	0.211	0.35
10 pulses	-1.337	49.1	105.32	-1.262	0.075	1.12
20 pulses	-1.258	172.9	171.68	-	-	4.00
30 pulses	-1.242	316.6	207.83	-	-	7.23

Fig. 8 Corrosion rates calculated by Eq. (1)

Fig. 9 Results of EIS test: a Nyquist plots, b |Z| versus frequency of Bode plots, c phase angle versus frequency of Bode plots

Fig. 10 EEC used in EIS data analysis of AZ91 Mg alloy: a untreated and treated by HCPEB at the pulses of 20 and 30, b treated by HCPEB at the pulses of 3, 5 and 10

Table 3 Fitting results of EIS results of the samples in SBF solution

Pulses of HCPEB	R_s (ohm cm²)	CPE (×10^-6 O^-1 cm^-2 sⁿ)	n	R_ct (ohm cm²)	C_f (μF/cm²)	R_f (ohm cm²)	L_ads (H cm^-2)	R_ads (ohm cm²)	R_p (ohm cm²)
Untreated	24.2	43.39	0.88	146.0	1952.0	62.8	183.1	35.2	208.8
3 pulses	30.3	33.02	0.81	427.4	758.8	159	-	-	586.4
5 pulses	36.0	27.78	0.81	592.2	483.2	262.3	-	-	854.5
10 pulses	20.6	40.74	0.82	474.7	904.6	133.6	-	-	608.3
20 pulses	28.4	52.90	0.76	129.7	914.1	14.8	30.41	20.3	144.5
30 pulses	25.6	133.1	0.83	93.8	925.3	12.9	7.39	15.3	106.7

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