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Effect of Adding RE and Ti Elements on Microstructure and Corrosion Resistance of Zn-2.5Al-3Mg Alloy  PDF

  • Chen Wenxuan 1 ✉
  • Zhou Guorong 1 ✉
  • Wang Xuefeng 1
  • Ma Longyue 1
  • Zhao Degang 1
  • Li Yongsheng 2
  • Wang Dong 2
  • Qin Bilian 3
1. School of Materials Science and Engineering, University of Jinan, Jinan 250022, China； 2. Shandong Quality Inspection and Testing Center of Construction Engineering Co., Ltd, Jinan 250031, China； 3. Shandong Huankeyuan Environmental Engineering Co., Ltd, Jinan 250013, China

Updated：2023-08-25

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Abstract

The effect of addition of RE and Ti on the microstructure and corrosion resistance of Zn-2.5Al-3Mg alloy were investigated by XRD, SEM, TEM and XPS. Results reveal that the microstructure of the Zn-2.5Al-3Mg alloy is composed of Zn-rich phase, binary eutectic (Zn-MgZn2/Mg2Zn11) and ternary eutectic (Zn/Al/Mg2Zn11). New phases of (Ce1‒xLax)Zn11 and Al2Ti appear with the addition of RE and Ti elements. Electrochemical impedance spectroscopy indicates that the corrosion resistance of Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy can be significantly improved compared to that of Zn-2.5Al-3Mg alloy. XPS analysis results show that the addition of RE element promotes the formation of Zn5(CO3)2(OH)6 and MgAl2O4 in the corrosion products, while the simultaneous addition of RE and Ti elements promotes the formation of corrosion products Zn5(CO3)2(OH)6, ZnAl2O4 and MgAl2O4, and inhibits the formation of loose porous ZnO. Zn5(CO3)2(OH)6, ZnAl2O4 and MgAl2O4 attach well to the surface of the sample, which provides a dense protective layer for the alloys, thus improving the corrosion resistance of Zn-2.5Al-3Mg alloy.

With the increasing demands for the corrosion resistance of steel in industry, the traditional hot-dip galvanizing cannot meet the demand. The corrosion resistance of the alloy can be further improved by the addition of alloying element like aluminum[

1–2], such as Galfan coatings, of which the corrosion resistance is about three times higher than that of pure zinc coatings, which has been widely used in construction, automotive processing and other fields[3–4]. At present, Zn-Al-Mg series coatings have been extensively studied, due to their corrosion resistance superior to that of traditional Zn and Zn-Al series coatings[5–7].

In the past 20 years, many Zn-Al-Mg alloys have been studied, such as the famous ZAM (Zn-6Al-3Mg) produced by Nissin steel corporation of Japan[

8] and PosMAC (Zn-2.5Al-3Mg) produced by POSCO of South Korea[9]. In order to expand the application and to prolong the service life of Zn-Al-Mg alloy, researchers begin to study the effect of element addition on Zn-Al-Mg alloy. Li et al[10] found that the addition of RE can homogenize the structure of Zn-6Al-3Mg alloy and inhibit intergranular corrosion. Guo et al[11] studied the influence of electrochemical properties on surface micromorphology of Zn-Al-Mg-RE alloy coatings. It is found that the addition of RE can improve the corrosion resistance of the alloy. Han et al[12] studied the effect of RE co-doping on corrosion behavior of Zn-Al-Mg hot-dip galvanizing coatings used for transmission towers. It was found that the addition of RE can refine the microstructure of Zn-Al-Mg alloy, and then significantly improve the corrosion resistance of the alloy.

In addition, Ti is a metal with relatively strong passive stability and can form a protective oxide film[

13–14]. Dong et al[15] found that adding Ti element to Zn-55Al alloy can significantly improve the corrosion resistance of the alloy. Cui et al[16] found that the self-corrosion current density of Zn-5Al-0.15Ti alloy coating is smaller than that of Zn-5Al alloy coating, demonstrating that the addition of Ti can slow down the corrosion of the alloy. However, there is little report on the effect of adding RE and Ti simultaneously on the microstructure and corrosion resistance of Zn-Al-Mg alloy. Therefore, the aim of this work is to investigate the effect of RE and Ti on the microstructure and corrosion behavior of Zn-Al-Mg alloy.

1 Experiment

Zn-2.5Al-3Mg, Zn-2.5Al-3Mg-0.1RE (RE refers to La and Ce) and Zn-2.5Al-3Mg-0.1RE-xTi (x=0.1, 0.2, 0.3, 0.4) alloys were prepared by casting method. The metals of Zn (99.99wt%), Al (99.5wt%), Mg (99.99wt%), Mg-20RE and Al-15Ti were melted in electrical resistance furnace at 750 °C for 2 h for dissolving and homogenizing. Afterwards, the melt was cooled to 550 °C and kept for a certain time. Finally, the melt was cast into the mold under atmospheric conditions to obtain the alloy ingot required for the experiment.

The microstructure of prepared specimens was observed by scanning electron microscope (SEM; FEG-250) equipped with back scattered electron (BSE). The energy dispersive spectroscopy (EDS) attached to SEM was used to analyze the elemental composition of the alloys. The characterization was performed by transmission electron microscope (TEM; JEM-2100) equipped with EDS. Additionally, the phase was identified by X-ray diffraction (XRD; D8 advance). A step-scan mode was used at the 2θ range from 10° to 90°.

The electrochemical measurements were conducted on IM6d Zahner-Elektrik workstation. Three-electrode system composed of working electrode (Zn-based alloys with 1cm2 in test surface), counter electrode (Pt electrode) and reference electrode (saturated calomel electrode, SCE) was used to evaluate the corrosion behavior of the alloys. Electrochemical impedance spectroscopy (EIS) test was conducted under the sinusoidal potential perturbation of ±10 mV in the frequency range of 10-1 Hz to 10-1 mHz. The samples were subjected to dynamic polarization after stabilizing the open circuit potential (OCP) for 30 min in all the experiments. The scanning rate of dynamic polarization was 10 mV/s. All electrochemical measurements were conducted in the 3.5wt% NaCl solution at room temperature. The surface corrosion products of the alloys were analyzed by X-ray photoelectron spectroscopy (XPS; ESCALAB Xi+). The fitting procedure was carried out by Avantage software considering linear background, and C 1s peak of adventitious carbon at a binding energy of 284.8 eV was used to normalize the absolute energy.

2 Results and Discussion

2.1 Microstructure characteristics

The XRD patterns of Zn-2.5Al-3Mg, Zn-2.5Al-3Mg-0.1RE and Zn-2.5Al-3Mg-0.1RE-0.2Ti alloys are presented in Fig.1. It should be noted that Zn, MgZn2, Mg2Zn11 phases are identified in all alloys[

17–18]. The addition of Ti in Zn-2.5Al-3Mg-0.1RE leads to new phase (Al2Ti). The diffraction peaks of Al and RE are not detected, which may be due to the lower content or the formation of fewer phases. There is a strong preferred orientation because the samples are as-cast. Zn has the preferential orientations of Zn (0002), Zn (101¯0) and Zn (101¯1) at 2θ value of 36°, 39° and 43°, respectively.

Fig.1  XRD patterns of Zn-2.5Al-3Mg, Zn-2.5Al-3Mg-0.1RE and Zn-2.5Al-3Mg-0.1RE-0.2Ti alloys

The microstructure of Zn-2.5Al-3Mg alloy is shown in Fig.2. The EDS data of the points marked in Fig.2 are presented in Table 1. It can be found that the microstructure of the Zn-2.5Al-3Mg alloy is composed of Zn-rich phase, binary eutectic and ternary eutectic. EDS analyses in Table 1 reveal that the compositions of the black area (point 1), bright white area (point 2), and light grey area (point 3) in the binary eutectic (Fig.2a) are MgZn2, Zn-rich, Mg2Zn11 phases respectively. Based on the phase diagram of Zn-Al-Mg alloy, MgZn2 phase firstly forms as the primary phase and then transforms to Mg2Zn11 in the peritectic reaction: MgZn2+L→Mg2Zn11[

19–20]. However, this transition is different from the actual crystallization rate, so the microstructure of the alloy shows that the MgZn2 phase is surrounded by Mg2Zn11 phase (Fig.2a). Fig.2b shows the enlarged region of the ternary

Fig.2  Microstructure (a) and EDS analysis points of Zn-2.5Al-3Mg alloy

Table 1  EDS results of different points marked in Fig.2 (at%)
PointZnAlMg
1 63.17 1.68 35.15
2 97.66 2.34 -
3 82.47 3.30 14.24
4 88.66 7.05 4.29
5 77.71 8.55 13.74
6 69.50 26.23 4.27

eutectic. Combined with EDS analysis results, the ternary eutectic consists of Zn, Al, Mg2Zn11 phases. As observed in Fig.2b, the Zn-rich phase and Mg2Zn11 phase are distributed in

layers, while the black granular Al-rich phase is attached between them.

Fig.3 presents the surface morphologies of Zn-2.5Al-3Mg-0.1RE-xTi (x=0, 0.1, 0.2, 0.3, 0.4) alloys. The phase compositions of the alloys are determined by EDS, and corresponding results are illustrated in Table 2. As indicated in Fig.3, the addition of RE and Ti elements cannot change the microstructure of the alloy. However, the phase composition is different from that of Zn-2.5Al-3Mg alloy. Zn-2.5Al-3Mg-0.1RE alloy is composed of primary Zn, binary eutectic (Zn-MgZn2/Mg2Zn11), ternary eutectic (Zn/Al/Mg2Zn11), and white massive phase. Combined with EDS results in Table 2 (point 1), it suggests that the white massive phase is (Ce1-xLax)Zn11 (x=0.41)[

21]. The phase composition of the Ti-added alloy is similar to that of Zn-2.5Al-3Mg-0.1RE, and the difference is that there are primary Al phase (point 4 in Table 2) and black regular objects. The atomic ration of the black regular object is close to Al:Ti=2:1 (point 3 in Table 2), so it is considered as Al2Ti phase. This result is consistent with XRD analysis in Fig.1.

Fig.3  SEM microstructures of Zn-2.5Al-3Mg-0.1RE-xTi alloys: (a) x=0, (b) x=0.1, (c) x=0.2, (d) x=0.3, and (e) x=0.4

Table 2  EDS results of points marked in Fig.3c (at%)
PointZnAlMgTiLaCe
1 89.53 2.21 - - 3.35 4.91
2 68.58 1.80 29.62 - - -
3 23.94 50.87 0.12 24.88 0.09 0.10
4 54.77 45.23 - - - -

As shown in Fig.3a‒3e, when RE element is added to Zn-2.5Al-3Mg alloy alone, the average grain size of binary eutectic structure is almost the same as that without RE element. However, after the addition of Ti, the grain size of binary eutectic structure is significantly reduced (marked by white circles in Fig.3a‒3e), and its number is also significantly increased. Meanwhile, it can also be clearly observed that granular Al-rich phase is distributed at the grain boundary of binary eutectic grains (yellow arrows marked in Fig.3b‒3e). Moreover, with the increase in Ti element (Y=0.1‒0.4), the grain size of binary eutectic structure first decreases and then increases. When X=0.2, the amount of MgZn2 phase reaches the maximum in all six alloys. Some studies have proved that the existence of MgZn2 phase can greatly improve the corrosion resistance of the alloy[

22–23]. In other words, the corrosion resistance of Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy may be the best among the six alloys, which needs to be further proved by the subsequent electrochemical performance analysis.

The EDS mapping of Zn-2.5Al-3Mg, Zn-2.5Al-3Mg-0.1RE and Zn-2.5Al-3Mg-0.1RE-0.2Ti alloys are shown in Fig.4. As observed in Fig.4a, the Al-rich phase is mainly distributed in the ternary eutectic structure, and the Mg and Zn elements combine to form the MgZnx phase. In the Zn-2.5Al-3Mg-0.1RE alloy, the distribution of Al and Mg elements is similar to that of Zn-2.5Al-3Mg. The white hexagonal object is mainly composed of Zn, La and Ce elements (Fig.4b). Ti

Fig.4  EDS mappings of Zn-2.5Al-3Mg (a), Zn-2.5Al-3Mg-0.1RE (b) and Zn-2.5Al-3Mg-0.1RE-0.2Ti (c) alloys

element is mainly combined with Al to form AlTix phase in the alloys containing Ti element. In comparison, it is obviously observed that granular Al-rich phase is distributed at the grain boundary of binary eutectic grains in the alloys containing Ti element (marked with yellow arrows). In addition, the distribution of Al element is in the same ternary eutectic structure as that in Zn-2.5Al-3Mg and Zn-2.5Al-3Mg-0.1RE alloys.

In order to further analyze the phase structure of the alloys added with RE and Ti elements, the Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy was selected for TEM analysis, and the results are shown in Fig.5. The electron diffraction spots in regions 1, 2, 3 and 4 in Fig.5a correspond to Fig.5c‒5f, respectively. The crystal face indexes are (0002), (1¯011), (1¯010) in the region 1, so the region 1 is hcp-Zn solid solution. The crystal face indexes in the region 2 are (111), (200), (11¯1¯), which is a solid solution of fcc-Al. The crystal face indexes of solid solution are (120), (320), (200) in the region 3, and the pattern is consistent with [004] Mg2Zn11. Therefore, it is identified as the Mg2Zn11 phase. The crystal face indexes of region 4 are (101¯0), (101¯3), (0003), which is a solid solution of hexagonal MgZn2 phase. Veys-Renaux et al[

21] described the substitution of Ce with La at constant Zn ratio, treated as the formula (Ce, La)aZnb in the Ce-La-Zn ternary system. The bright-filed image of the TEM of the (Ce, La)aZnb phase is shown in Fig.5b, and the corresponding EDS results are presented in Fig.5g. The atomic ratio of Ce and La elements to Zn element is close to 1:11, so the phase is identified as the (Ce1-xLax)Zn11 phase. The results are consistent with SEM analysis (Fig.3).

Fig.5  TEM images of Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy (a, b); corresponding SAED patterns of region 1 (c), region 2 (d), region 3 (e) and region 4 (f); EDS result of region 5 (g)

2.2 Electrochemical impedance spectroscopy (EIS)

The corrosion behavior of the six alloys in 3.5wt% NaCl solution was studied by electrochemical impedance measure-ments, and the Nyquist and Bode plots are shown in Fig.6. The Bode phase angle diagram in Fig.6b shows the wave crest in a frequency range of 102‒103 Hz for tested specimens, indicating that the corrosion mechanisms of the six alloys are the same. Additionally, it is clearly found that the capacitance arc radius of the alloys with RE and Ti elements is larger than that of the Zn-2.5Al-3Mg alloy in Fig.6a. The larger the capa-citance arc radius, the higher the charge transfer resistance, and the more difficult the corrosion of the alloy[

24–25]. Moreover, Bode modulus plots in Fig.6c suggest that impedance of the alloys with RE and Ti elements is higher than that of the Zn-2.5Al-3Mg alloy. The results indicate that the addition of RE and Ti elements can significantly improve the corrosion resistance of Zn-2.5Al-3Mg alloy.

Fig.6  EIS results of Zn-2.5Al-3Mg, Zn-2.5Al-3Mg-0.1RE and Zn-2.5Al-3Mg-0.1RE-xTi alloys in 3.5wt% NaCl solution: (a) Nyquist diagrams, (b) Bode phase angle diagrams, (c) Bode impedance diagrams, and (d) equivalent circuit

To compare the corrosion resistance of the six alloys more intuitively, a fitting equivalent circuit mode is given in Fig.6d based on the EIS data. Table 3 shows the fitting results. In Fig.6d, Rs is the solution resistance, Rf is the resistance of surface products, and Rct is the charge transfer resistance. CPE1 and CPE2 are constant phase angle elements, referring to the capacitance of the surface product layer and double layer, respectively. n represents the dispersion coefficient, and its dimensionless parameter range is 0‒1[

26–28]. The solution resis-tance Rs of all samples is not only are lower than 10 Ω·cm2, but also much lower than Rf and Rct. This indicates that all samples are in a stable testing environment[17]. It is worth noting that the corrosion product resistance Rf of the Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy is higher than that of other alloys, indicating that the corrosion product layer of Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy is more compact than that of other alloys. In addition, the Rct of the Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy is also higher than that of other alloys, indicating that it is more difficult to corrode. Therefore, the corrosion resistance of Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy is the best among these alloys.

Table 3  Equivalent circuit parameters obtained via fitting the EIS data of alloys
SampleRs/Ω·cm2CPE1/Ω-1·s-n·cm-2n1Rf/Ω·cm2CPE2/Ω-1·s-n·cm-2n2Rct/Ω·cm2λ2/×10-4
Z (Zn-2.5Al-3Mg) 9.69 4.465 4×10-5 0.809 92 766.1 1.6374×10-3 1 774 15.55
Z-0.1RE 8.354 2.179 4×10-5 0.855 76 591.6 2.463×10-4 0.374 9 113 2 5.223
Z-0.1RE-0.1Ti 8.153 8.634 6×10-6 0.887 15 315 1 9.6009×10-5 0.568 35 354 8 3.227
Z-0.1RE-0.2Ti 7.575 8.014×10-6 0.896 81 342 8 4.2349×10-5 0.302 18 687 5 2.993
Z-0.1RE-0.3Ti 9.011 9.808 7×10-6 0.898 96 325 5 4.5899×10-5 0.601 05 356 4 1.406
Z-0.1RE-0.4Ti 7.509 2.064 9×10-5 0.900 38 116 3 2.7638×10-4 0.699 23 213 0 24.97

2.3 Potentiodynamic polarization

Comparison of polarization curves of Zn-2.5Al-3Mg, Zn-2.5Al-3Mg-0.1RE and Zn-2.5Al-3Mg-0.1RE-xTi alloys in 3.5wt% NaCl solution is shown in Fig.7. The corrosion potential Ecorr and the corrosion current density Icorr can be obtained by Tafel extrapolation, and the corresponding values are shown in Table 4. The corrosion potential and the corrosion current density of Zn-2.5Al-3Mg are -1.534 V and 1.2942×10-4 A/cm2, respectively. It is clearly observed that corrosion potential of the alloys added with RE and Ti elements is considerably larger (positive) as compared to that of Zn-2.5Al-3Mg alloy, and the corrosion current density is lower than that of Zn-2.5Al-3Mg alloy. It suggests that the addition of RE and Ti elements can significantly improve the corrosion resistance of Zn-2.5Al-3Mg alloy. However, it is worth noting that the Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy has the largest corrosion potential and the smallest corrosion current density among these alloys. This may be due to the more precipitated MgZn2 phase and the more uniform grain distribution.

Fig.7  Potentiodynamic polarization curves of Zn-2.5Al-3Mg, Zn-2.5Al-3Mg-0.1RE and Zn-2.5Al-3Mg-0.1RE-xTi alloys in 3.5wt% NaCl solution

Table 4  Electrochemical parameters calculated from potentiodynamic polarization test
SampleEcorr/VIcorr/×10‒5 A·cm‒2
Z (Zn-2.5Al-3Mg) ‒1.534 12.942
Z-0.1RE ‒1.482 3.2589
Z-0.1RE-0.1Ti ‒1.471 5.1511
Z-0.1RE-0.2Ti ‒1.399 3.1376
Z-0.1RE-0.3Ti ‒1.450 4.7686
Z-0.1RE-0.4Ti ‒1.477 8.8418

2.4 Characterization of corrosion products

The corrosion products of Zn-2.5Al-3Mg, Zn-2.5Al-3Mg-0.1RE and Zn-2.5Al-3Mg-0.1RE-0.2Ti alloys immersed in 3.5wt% NaCl solution were analyzed by XPS. The results are displayed in Fig.8. It can be seen that C, O, Zn, Al, Mg elements are present in all three alloys, while the added RE and Ti elements are not detected, probably because the added amount is too small or cross-section is small. The narrow spectra of C, O, Zn, Al, Mg elements are fitted by Avantage software. In addition, at a binding energy of 284.8 eV, the charge shift in the measured XPS spectra is corrected for the C 1s peak of the adventitious carbon. In Fig.8a, carbon exists in two forms in the Zn-2.5Al-3Mg alloy: (1) C-C bond with binding energy of 284.82 eV, which is from adventitious carbon contaminants, and (2) O-C=O bond with binding en-ergy of 289.22 eV. However, carbon exists in four ways: C-C, C-O-C, O-C=O and carbonates in the Zn-2.5Al-3Mg-0.1RE and Zn-2.5Al-3Mg-0.1RE-0.2Ti alloys (Fig.8b and 8c)[

29–30]. Fig.8d‒8f present the O 1s spectra of Zn-2.5Al-3Mg, Zn-2.5Al-3Mg-0.1RE and Zn-2.5Al-3Mg-0.1RE-0.2Ti alloys, respectively. In the Zn-2.5Al-3Mg alloy, the O 1s spectra benefit from two contributions: hydroxides and metal oxides. In Fig.8e and 8f, the O 1s spectrum contains three peaks, at the binding energy of 532.07, 531.33 and 530.16 eV (approximately), corresponding to hydroxides, carbonates and metal oxides, respectively[6].

Fig.8  XPS spectra of Zn-2.5Al-3Mg, Zn-2.5Al-3Mg-0.1RE and Zn-2.5Al-3Mg-0.1RE-0.2Ti alloys: (a‒c) C 1s, (d‒f) O 1s, (g‒i) Zn 2p3/2, (j‒l) Al 2p, and (m‒o) Mg 1s

Analysis of the Zn 2p3/2 spectrum (Fig.8g) indicates the presence of Zn(OH)2 and ZnO in the Zn-2.5Al-3Mg alloy. Nevertheless, Zn mainly exists in the form of hydrozincite Zn5(CO3)2(OH)6 in Zn-2.5Al-3Mg-0.1RE alloy (Fig.8h). As shown in Fig.8i, Zn is found in two chemical states for Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy, which are hydrozincite Zn5(CO3)2(OH)6 and spinel oxides ZnAl2O4[

31–32]. Fig.8j‒8l exhibit the XPS spectra of the Al 2p of the three alloys. Two different peaks are found (Fig.8j), i.e. aluminum metal (Al0) and oxidized aluminum (Al3+). For Zn-2.5Al-3Mg-0.1RE and Zn-2.5Al-3Mg-0.1RE-0.2Ti alloys, the Al 2p spectra all have one peak, at the binding energy of 74.05 and 74.03 eV respectively, which indicates the presence of Al2O3[32–33]. As for the spectrum of Mg 1s in Fig.8m, it reveals the presence of one component, mostly Mg(OH)2 at around 1302.89 eV. The Mg 1s peak is centered at 1304 eV, a binding energy value close to MgAl2O4, for both Zn-2.5Al-3Mg-0.1RE and Zn-2.5Al-3Mg-0.1RE-0.2Ti alloys in Fig.8n‒8o.

In summary, the corrosion products of the investigated Zn-2.5Al-3Mg alloy are composed of Zn(OH)2/ZnO, Al2O3, Al metal and Mg(OH)2. The corrosion products of Zn-2.5Al-3Mg-0.1RE alloy mainly consist of hydrozincite Zn5(CO3)2(OH)6, Al2O3 and MgAl2O4. The corrosion products are composed of hydrozincite Zn5(CO3)2(OH)6, ZnAl2O4, Al2O3 and MgAl2O4 in the Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy. It can be observed that the corrosion products change greatly after the addition of RE element. Compared with Zn-2.5Al-3Mg-0.1RE alloy, the corrosion products of the alloy added with Ti element change slightly. In the initial stage of corrosion, the open circuit potential of MgZn2 is low, and it acts as the anode to release Zn2+ and Mg2+. Oxygen is reduced in the cathode region to generate hydroxide ions. In addition, carbon dioxide in the air enters the solution and reacts to produce carbonate ions[

33].

MgZn2→Mg2++2Zn2++6e- (1)
2H2O+2e-→H2+2OH- (2)
O2+4e-+2H2O→4OH- (3)
CO2+ H2O+2e-→CO32-+H2 (4)

Zn2+ cannot only react with OH- to form Zn(OH)2, but also react with OH- and CO32- simultaneously to form hydrozincite Zn5(CO3)2(OH)6. Zn(OH)2 can be further decomposed into ZnO with loose pores and low adhesion. However, Mg2+ will also react with OH- to form Mg(OH)2. Subsequently, with the increase in OH-, the pH value increases. The electrode potential of Al is lower than that of Zn in the alkaline solution. Al acts as the anode to react with OH- to form Al(OH)4-, while the Zn is protected as the cathode[

34]. Finally, Zn2+ and Mg2+ react with Al(OH)4- to form ZnAl2O4 and MgAl2O4 with spinel structure, respectively.

4Al+4OH-→4Al(OH)4-+3e- (5)
Zn2++2OH-→Zn(OH)2→ZnO+H2O (6)
5Zn2++6OH-+2CO32-→Zn5(CO3)2(OH)6 (7)
Mg2++2OH-→Mg(OH)2 (8)
Mg2++2Al(OH)4-→MgAl2O4+4H2O (9)
Zn2++2Al(OH)4-→ZnAl2O4+4H2O (10)

Zn5(CO3)2(OH)6 has a compact structure and can adhere to the surface of the alloy well, thereby slowing down the corrosion of the alloy[

35]. Related research[36] reveals that ZnAl2O4 and MgAl2O4 with spinel structure in the alloys are useful for improving the corrosion resistance. Noticeably, the addition of RE and Ti elements inhibits the formation of ZnO and promotes the formation of Zn5(CO3)2(OH)6 and MgAl2O4. In addition, spinel ZnAl2O4 is also found in corrosion products of alloys containing Ti element. This indicates that adding RE and Ti at the same time can improve the corrosion resistance of the alloys more significantly than adding RE element alone. Therefore, the corrosion resistance of Zn-2.5Al-3Mg alloy is greatly improved by adding RE and Ti elements.

3 Conclusions

1) The microstructure of the Zn-2.5Al-3Mg alloy is com-posed of Zn-rich phase, Zn-MgZn2/Mg2Zn11 binary eutectic and Zn/Al/Mg2Zn11 ternary eutectic. Zn-2.5Al-3Mg-0.1RE alloy consists of Zn-rich phase, (Ce1-xLax)Zn11 (x=0.41) phase, Zn-MgZn2/Mg2Zn11 binary eutectic and Zn/Al/Mg2Zn11 ternary eutectic. Zn-2.5Al-3Mg-0.1RE-xTi alloy is composed of Zn-rich phase, Al-rich phase, Al2Ti phase, Zn-MgZn2/Mg2Zn11 binary eutectic and Zn/Al/Mg2Zn11 ternary eutectic.

2) The addition of RE element does not change the size of the binary eutectic. However, the binary eutectic size of alloys containing Ti element is greatly reduced. Among these alloys, when the addition amount is 0.2%, the size is the smallest, the number of MgZn2 is the largest, and the structure distribution is uniform.

3) Among the six tested alloys, the Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy has the highest surface product resistance Rf and charge transfer resistance Rct values, and its corrosion potential is the most positive and the corrosion current density is the smallest, indicating that the Zn-2.5Al-3Mg-0.1RE-0.2Ti alloy has the best corrosion resistance.

4) The corrosion products of Zn-2.5Al-3Mg alloy include Zn(OH)2/ZnO, Al2O3, Al metal and Mg(OH)2. The corrosion products are composed of Zn5(CO3)2(OH)6, Al2O3 and MgAl2O4 in Zn-2.5Al-3Mg-0.1RE alloy. Compared with the Zn-2.5Al-3Mg-0.1RE alloy, the corrosion products of the alloy contain-ing Ti element have ZnAl2O4. Zn5(CO3)2(OH)6, ZnAl2O4 and MgAl2O4 can be well attached to the surface of the sample, which provides a certain barrier for the corrosion of the sample, thereby slowing down the corrosion rate of the alloy.

References

1

Wang Huaitao, Liu Zili, Xu Wenlong et al. Corrosion Protec- tion[J], 2013, 34(2): 133 (in Chinese) [Baidu Scholar] 

2

Liu Anqiang, Xiao Kui, Li Xiaogang et al. Thermal Spray Technology[J], 2015, 7(4): 46 (in Chinese) [Baidu Scholar] 

3

Qiao Tengbo. Study of Processs and Corrosion Mechanism of Hot-Dip Galfan Coating[D]. Tianjin: Hebei University of Tech-nology, 2014 (in Chinese) [Baidu Scholar] 

4

Gao Qiuzhi. Research on Microstructure and Process of Hot-Dipping Galfan Coating by Sendzimir[D]. Tianjin: Hebei Univer-sity of Technology, 2009 (in Chinese) [Baidu Scholar] 

5

Prosek T, Persson D, Stoulil J et al. Corrosion Science[J], 2014, 86: 231 [Baidu Scholar] 

6

Wang Yanqi, Kong Gang, Che Chunshan. Corrosion[J], 2019, [Baidu Scholar] 

75(2): 203 [Baidu Scholar] 

7

Prosek T, Hagström J, Persson D et al. Corrosion Science[J], 2016, 110: 71 [Baidu Scholar] 

8

Lin Anbang. Study on the Microstructure and Performance of Hot Dipping Zn-6Al-3Mg Alloy Coating[D]. Tianjin: Hebei University of Technology, 2014 (in Chinese) [Baidu Scholar] 

9

Sohn I R, Kim T C, Ju G I et al. Corrosion Science Techno- [Baidu Scholar] 

logy[J], 2021, 20(1): 7 [Baidu Scholar] 

10

Li Shiwei, Gao Bo, Yin Shaohua et al. Applied Surface Sci- [Baidu Scholar] 

ence[J], 2015, 357: 2004 [Baidu Scholar] 

11

Guo Kai, Li Xingeng, Wang Xiaoming et al. International Journal of Electrochemical Science[J], 2016, 11: 5063 [Baidu Scholar] 

12

Han Yu, Xia Yanqiu, Chen Xin et al. Anti-corrosion Methods and Materials[J], 2018, 65(2): 131 [Baidu Scholar] 

13

Yang Sui, Su Xuping, Wang Jianhua et al. Journal of Alloys and Compounds[J], 2010, 499: 194 [Baidu Scholar] 

14

Gui Yan, Xu Qiaoyu. Electroplating Finishing[J], 2009, 28(3): 21 (in Chinese) [Baidu Scholar] 

15

Dong Xueqiang, Guo Taixiong, Li Feng et al. Materials Protection[J], 2015, 48(8): 63 (in Chinese) [Baidu Scholar] 

16

Cui Jun, Liu Zili, Liu Xiqin et al. Corrosion Protection[J], 2018, 39(4): 294 (in Chinese) [Baidu Scholar] 

17

Yao Caizhen, Lv Haibing, Zhu Tianping et al. Journal of Alloys and Compounds[J], 2016, 670: 239 [Baidu Scholar] 

18

Gogola P, Gabalcová Z, Kusý M et al. Materials[J], 2021, [Baidu Scholar] 

14(18): 5404 [Baidu Scholar] 

19

Bruycker E D, Zermout Z, Cooman B C D. Materials Science Forum[J], 2007, 58(539‒543): 1276 [Baidu Scholar] 

20

Li Li, Liu Yongchang, Gao Huixia et al. Journal of Materials Science-Materials in Electronics[J], 2013, 24(1): 336 [Baidu Scholar] 

21

Veys-Renaux D, Guessoum K, Rocca E et al. Corrosion Sci- ence[J], 2013, 77: 342 [Baidu Scholar] 

22

Li Kailiang, Wu Changjun, Peng Haoping et al. Chinese Journal of Engineering[J], 2016, 38(8): 1123 (in Chinese) [Baidu Scholar] 

23

Volovitch P, Allely C, Ogle K. Corrosion Science[J], 2009, [Baidu Scholar] 

51(6): 1251 [Baidu Scholar] 

24

Rai P K, Rout D, Kumar D S et al. Journal of Materials Engineering and Performance[J], 2021, 30(6): 4138 [Baidu Scholar] 

25

Chen Lin, Chen Changguo, Wang Ningning et al. Rare Metal Materials and Engineering[J], 2015, 44(2): 333 [Baidu Scholar] 

26

Zhou Hanyu, Hou Ruiqing, Yang Junjie et al. Journal of Alloys and Compounds[J], 2020, 840: 155 792 [Baidu Scholar] 

27

Xu Minyun, Han Dong, Zheng Zhaoyang et al. Surface and Coatings Technology[J], 2022, 444: 128 665 [Baidu Scholar] 

28

Jia Zheng, Yu Bing, Fu Li. Rare Metal Materials and Engineering[J], 2023, 52(2): 568 (in Chinese) [Baidu Scholar] 

29

Schürz S, Luckeneder G H , Fleischanderl M et al. Corrosion Science[J], 2010, 52(10): 3271 [Baidu Scholar] 

30

Ye Chengtong, Jia Lina, Xu Gaoxiang et al. Surface and Coatings Technology[J], 2019, 366: 214 [Baidu Scholar] 

31

Duchoslav J, Kehrer M, Truglas T et al. Applied Surface Sci- ence[J], 2020, 504: 144 457 [Baidu Scholar] 

32

Duchoslav J, Steinberger R, Arndt M et al. Corrosion Science[J], 2015, 91: 311 [Baidu Scholar] 

33

Zhou Shengguo, Yan Qingqing, Tang Chutian et al. Corrosion Science[J], 2019, 163: 108 254 [Baidu Scholar] 

34

Hao Yulin, Shen Hai, Zhao Yi. Paint and Coatings Industry[J], 2018, 48(12): 7 (in Chinese) [Baidu Scholar] 

35

Azevedo M S, Allely C, Ogle K et al. Corrosion Science[J], 2015, 90: 482 [Baidu Scholar] 

36

Zhu Zixin, Chen Dong, Xu Binshi. International Conference on Mechanical Materials and Manufacturing Engineering[C]. Switzerland: Trans Tech Publications, 2011: 727 [Baidu Scholar] 

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