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Acta Metall Sin  2018, Vol. 54 Issue (8): 1141-1149    DOI: 10.11900/0412.1961.2017.00484
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Comparative Study on Corrosion Behavior of Cast and Forged Mg-5Y-7Gd-1Nd-0.5Zr Alloys
Jinhui LIU1,2, Yingwei SONG1(), Dayong SHAN1, En-Hou HAN1
1 Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2 School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
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Abstract  

Magnesium and its alloys have become increasingly attractive in the automotive, 3C products and aerospace industries because of their advantages such as low density and high specific strength. In recent years, rare earth-Mg alloys have attracted much attention due to their high mechanical properties at room and elevated temperatures. Adjusting the microstructures by deformation treatment is a common method to improve the mechanical properties of Mg alloys. The microstructure especially the size, volume fraction and distribution of second phases in rare earth-Mg alloys will be changed during deformation treatment, which has a great effect on the corrosion resistance of Mg alloys. However, the studies on the effect of deformation treatment on the corrosion resistance of rare earth-Mg alloys are far away from sufficient. In this work, the corrosion behavior of cast and forged Mg-5Y-7Gd-1Nd-0.5Zr (EW75) alloys were studied by using SEM, XRD, mass loss measurements and electrochemical tests. The results indicate that the second phases are distributed along the grain boundaries of cast and forged EW75 alloys. Meanwhile, the second phases in forged EW75 alloy are finer and lower volume fraction than that in cast EW75 alloy. The micro-galvanic corrosion of the forged EW75 alloy is weaker in comparison with the cast EW75 alloy owing to the smaller size and lower volume fraction of second phases as well more compact surface film, resulting in the better corrosion resistance.

Key words:  Mg alloy      cast      forged      second phase      surface film      micro-galvanic corrosion     
Received:  20 November 2017     
ZTFLH:  O646  
Fund: Supported by National Key Research and Development Program of China (No.2016YFB0301105) and National Natural Science Foundation of China (No.51471174)

Cite this article: 

Jinhui LIU, Yingwei SONG, Dayong SHAN, En-Hou HAN. Comparative Study on Corrosion Behavior of Cast and Forged Mg-5Y-7Gd-1Nd-0.5Zr Alloys. Acta Metall Sin, 2018, 54(8): 1141-1149.

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https://www.ams.org.cn/EN/10.11900/0412.1961.2017.00484     OR     https://www.ams.org.cn/EN/Y2018/V54/I8/1141

Fig.1  Low (a, c) and high (b, d) magnified surface BSE-SEM images of the cast (a, b) and forged (c, d) EW75 alloys
Fig.2  EDS spectra of γ (a) and β (b) phases in Fig.1
Fig.3  Surface morphologies of the cast (a) and forged (b) EW75 alloys after etching
Fig.4  XRD spectra of the cast and forged EW75 alloys
Fig.5  Surface morphologies of the cast (a) and forged (b) EW75 alloys after immersion in 3.5%NaCl solution for 60 h (a) and 7 d (b)
Fig.6  Surface (a, b) and cross-sectional (c, d) morphologies of the cast EW75 alloy after immersion in 3.5%NaCl solution for 30 min (a, c) and 2 h (b, d) with removal of corrosion products
Fig.7  Low (a, c, e) and high (b, d, f) magnified surface morphologies of the forged EW75 alloys after immersion in 3.5%NaCl solution for 30 min (a, b), 2 h (c, d) and 24 h (e, f) with removal of corrosion products
Fig.8  Polarization curves comparison of cast and forged EW75 alloys in 3.5%NaCl solution
EW75 Ecorr / V icorr / (μAcm-2) bc / (-mVdec-1)
Cast
Forged
-1.75
-1.75
87.9
46.4
175
159
Table 1  Fitting results of polarization curves of EW75 alloys
Fig.9  EIS Nyquist plots and equivalent circuit of 自the cast and forged EW75 alloys in 3.5%NaCl solution (Rs—solution resistance, Qdl—electric double layer capacitance, Rt—charge transfer resistance, Qf—surface film capacitance, Rf—surface film resistance, L—inductance, RL—inductance resistance)
EW75 Rs
Wcm2
Qdl
mScm-2s-n
ndl Rt
Wcm2
Qf
mScm-2s-n
nf Rf
Wcm2
L
Hcm2
RL
Wcm2
Cast 19.04 19.04 0.93 220 5081 0.85 119.1 14120 2222
Forged 18.86 17.96 0.93 262 5910 0.71 222.6 14340 1764
Table 2  Fitting results of EIS spectra
Fig.10  Cross-sectional schematics of micro-galvanic corrosion of the cast (a, b) and forged (c, d) EW75 alloys before (a, c) and after (b, d) immersion in 3.5%NaCl solution
Fig.11  Cross-sectional schematics of surface film formation on the cast (a, b) and forged (c, d) EW75 alloys before (a, c) and after (b, d) immersion in 3.5%NaCl solution
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