Effects of Deformation Texture and Twins on the Corrosion Resistance of Rolled AZ31 Mg Alloy Under 5% Uniaxial Compression

doi:10.1007/s40195-017-0639-7

Abstract

Abstract:

The deformation texture and twin effect of rolled AZ31 Mg alloy on the corrosion resistance in simulated body fluid (SBF) at room temperature were examined by potentiodynamic polarization and electrochemical impedance spectra. The corrosion morphology evolution after being immersed in SBF for 24 h has been analyzed by scanning electron microscope. The results show that the inhomogeneous deformation leaded to the obvious differences in the microstructure. The corrosion rate of rolled AZ31 Mg alloy decreased dramatically in the transverse direction (TD) plane, which mainly consisted of {0001} deformation texture, making TD plane be a lower surface energy, and thus a higher corrosion resistance, while the corrosion resistance of the plane with 45° to TD direction (45TD plane) containing enormous {10-12} tension twins decreased after 5% uniaxial compression. The {10-12} tension twins accelerate the rate of corrosion procedure and pitting corrosion. Moreover, it is suggested that the deformation texture affects the corrosion behavior more than the twins do. This study indicates that the corrosion rate of AZ31 Mg alloy in SBF can be modified by the small uniaxial compression.

Key words: AZ31, Mg alloy, Twins, Texture, Corrosion resistance

Chen Wang, Hao Ding, Bing-Shu Wang, Kui Wang, Jing-Jing Shi, Jun-Feng Chen. Effects of Deformation Texture and Twins on the Corrosion Resistance of Rolled AZ31 Mg Alloy Under 5% Uniaxial Compression[J]. Acta Metallurgica Sinica (English Letters), 2017, 30(10): 921-930.

Figures/Tables 13

Fig. 1 a Microstructure and texture of the as-received AZ31 Mg sample; b {0001} plot figure of as-received AZ31 Mg sample; c schematic illustration of the sample preparation from the large homogenized plate

Fig. 2 Twin boundary maps: a TD plane, b 45TD plane, c RD plane of AZ31 Mg sample after 5% uniaxial compression

Table 1 Percentages of {10-12} twin boundaries generated during 5% uniaxial compression among the total boundaries in different planes

Type of twins	TD plane	45TD plane	RD plane
{10-12}	16.53%	22.58%	2.18%

Fig. 3 Orientation image maps: a TD plane, b 45TD plane, c RD plane; {0001} and {11-20} plot figures: d TD plane, e 45TD plane, f RD plane of AZ31 Mg sample after 5% uniaxial compression; the colors of the grains in the maps a-c correspond to the crystallographic axes of the grains

Fig. 4 Distribution of misorientation angle between grain boundaries: a TD plane, b 45TD plane, c RD plane of AZ31 Mg sample after 5% uniaxial compression

Table 2 Volume fractions of twins in different planes for the sample after 5% uniaxial compression

TD plane	45TD plane	RD plane
72%	59%	2%

Fig. 5 Potentiodynamic polarization curves of different planes of AZ31 Mg sample (after 5% uniaxial compression) in SBF solution

Table 3 Results obtained from potentiodynamic polarization curves of different planes of AZ31 Mg sample (after 5% uniaxial compression) in SBF solution

Planes	b_a (mV)	b_c (mV)	E_corr (V vs SCE)	I_corr (A/cm²)	R_P (Ω cm²)
TD plane	0.3560	0.4076	-1.469	3.086×10^-6	2.674×10⁴
45TD plane	0.3939	0.5478	-1.496	6.500×10^-6	1.531×10⁴
RD plane	0.5890	0.5391	-1.471	5.662×10^-6	2.159×10⁴

Fig. 6 EIS diagrams for the TD, 45TD and RD planes of AZ31 Mg sample (after 5% uniaxial compression) in SBF solution: a Nyquist plot, b Bode plot of |Z| versus frequency, c Bode plot of phase angle versus frequency, d simulated equivalent circuit

Table 4 Fitting parameters of different planes of AZ31 Mg sample (after 5% uniaxial compression) in SBF solution

Planes	R_e (Ω/cm²)	Q₁ (Ω^-1/cm² sⁿ)	n₁	R₁ (Ω cm²)	Q₂ (Ω^-1/cm² sⁿ)	n₂	R₂ (Ω cm²)	R_L (Ω cm²)	L (H/cm²)	χ²
TD plane	2.08	3.969×10^-5	0.89	728.3	4.416×10^-5	0.79	920.8	450.2	42.6	6.0×10^-4
45TD plane	2.28	1.727×10^-5	0.93	554.6	2.253×10^-5	0.92	616.7	903.5	112.3	2.1×10^-4
RD plane	2.19	2.357×10^-5	0.86	644.8	2.375×10^-5	0.85	800.2	835.4	102.5	3.8×10^-4

Fig. 7 SEM images of AZ31 Mg sample (after 5% uniaxial compression) immersed in SBF for 24 h: a TD plane, b RD plane, c 45TD plane, d partial enlargement of 45TD plane in c

Table 5 Elemental compositions of different planes of AZ31 Mg sample (after 5% uniaxial compression) immersed in SBF for 24 h, spots 1-4 are indicated in Fig. 7

Region	Elemental composition (wt%)							Ca/P ratio
Region	O	Mg	Al	P	Ca	Na	Cl	Ca/P ratio
Spot 1 (TD plane)	7.4	84.04	3.27	2.44	2.84	-	-	1.16
Spot 2 (TD plane)	24.10	55.74	1.86	7.29	10.08	0.93	-	1.38
Spot 3 (RD plane)	39.44	19.62	0.79	14.59	24.92	0.65	-	1.71
Spot 4 (45TD plane)	55.46	0.61	-	14.38	25.65	0.61	0.73	1.78

Fig. 8 XRD patterns of the corrosion productions of AZ31 Mg sample (after 5% uniaxial compression) immersed in SBF for 24 h: a TD plane, b 45TD plane, c RD plane

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