ECAP of magnesium alloy Mg-Zn-Nd Tensile Properties

Of: Yingjie Li Feng Chen Lijia Zhang Xiuzhi

Abstract: The article at different temperatures and different strain rate tensile tests carried out to study the experimental temperature and strain rate on the path at different passes and ECAP of Mg-Zn-Nd alloy Superplastic Behavior . flow stress and strain rate results show that after four times after ECAP C Mg-Zn-Nd alloy, the elongation best; flow stress with the experimental temperature dependence indicates that, after equal channel angular extrusion after pressure Mg-Zn-Nd alloy superplastic deformation mechanism of grain boundary diffusion should be controlled by grain boundary sliding.

Keywords: ECAP; experiment; magnesium alloy
Abstract: In this paper, the influence of temperature and strain rate on the superplastic deformation behaviors of the ECAPed Mg-Zn-Nd alloy has been investigated by performing tensile tests at different temperatures and strain rates. It is showed that After 4 passes of ECAP by route C, the elongation of Mg-Zn-Nd alloy reached 381.8% at 300 ��, indicating that the ECAPed Mg-Zn-Nd alloy exhibited a good superplasticity. The curves of stress vs. temperature indicate that for the Mg-Zn- Nd alloy processed by ECAP, the dominant mechanism during superplastic deformation is grain boundary sliding controlled by grain boundary diffusion, whereas the nucleation, growth and coalition of cavities take effect as an important accommodating mechanism.

Keywords:: channel corner extrusions; experiment; magnesium alloy

ECAP Technology as the ultra-fine grain metals and alloys in the manufacturing Technology has aroused people's attention. Currently using this Technology has been in copper, aluminum, magnesium, nickel, iron and other alloys to obtain a fine grain structure, confirmed its is an innovative and effective method of grain refining. grain refinement can not only improve the mechanical properties, but also reduce the brittle - ductile transition temperature, even at low temperature or high strain rate superplasticity, thereby enhancing the alloy at room temperature formability, superplastic forming this alloy is important.

1 Materials and methods
1.1 Materials
The materials used in the experiments Mg-Zn-Nd magnesium alloy, which Zn content 1wt%, Nd content of 2wt%. Compressional deformation Mg-Zn-Nd alloys by magnesium alloy ingot at a temperature of 230 �� extrusion ratio was 35:1, the export rate of 2.5 m / min under the conditions of the hot extrusion get.

1.2 magnesium alloy ECAP
Use of channel angle is 90 �� (90 �� when the sample during extrusion shear force suffered the biggest), the channel diameter of 14 mm in equal channel angular extrusion die and the electronic universal magnesium alloy extrusion machine 1 to 4 pass equal channel angular extrusion, extrusion path used were A, BC and C.

ECAP 1.3 Superplasticity of magnesium alloy tensile test
To study the extrusion path, test temperature and strain rate on each pass through the ECAP processed magnesium alloy superplastic behavior, the CSS-55100 electronic universal testing machine on superplastic tensile test (sample size shown in Figure 1 .) test with displacement control mode, test the temperature range between 200 �� ~ 300 ��, initial strain rate range of 1 �� 10-4s-1 ~ 5 �� 10-3s-1 between.

1.4 Strain rate sensitivity and plastic flow activation energy determined
The multi-specimen test method to determine the tensile constant strain rate sensitivity, is about a series of samples at the same temperature at different constant stretch to the steady state, to make each specimen true stress - true strain curve. Then, in the other strain at the selected value of flow stress, according to type

Links to Research Papers Download http://www.hi138.com 2 Experimental results and analysis
2.1 ECAP of Mg-Zn-Nd alloy tensile test
Figure 2 shows the path through the various passes and ECAP of Mg-Zn-Nd alloy in 1 �� 10-4s-1 strain rate and temperature under different experimental elongation. The figure shows that when temperature at 300 �� and elongation are improved greatly. at 200 ��, the ECAP was only after a time extension was 63.87%; 2 times the elongation rate of 75.1% ~ 79.8 %; four times the elongation rate of 96.3% ~ 105.7%. at 250 ��, the ECAP was only after a time extension was 86.41%; 2 times the elongation rate of 93.2% ~ 117.8% ; four times the elongation rate of 120.9% ~ 129.5%. At 300 ��, the ECAP was only after a time extension was 282.9%; two times the elongation rate of 296.3% ~ 316.3%; 4 times the elongation rate of 337.8% ~ 381.8%.

2.2 ECAP Mg-Zn-Nd alloy plastic flow activation energy

The strain rate 1 �� 10-4s-1 under the conditions of the true strain is 0.15, the true stress as the flow stress obtained Mg-Zn-Nd alloy four times the flow stress and temperature curves, respectively Figure 3, Figure 4 and Figure 5. According to equation (4), can be calculated Mg-Zn-Nd alloy in 1 �� 10-4s-1 strain rate plastic flow activation energy, respectively, 186.15 kJ / mol, 165.77 kJ / mol and 111.08 kJ / mol. In general, for the purposes of magnesium alloy, the grain boundary diffusion activation energy of 92 kJ / mol. Obviously, after four plays 3 different paths ECAP processed Mg-Zn-Nd magnesium Plastic flow activation energy of the alloy grain boundary diffusion activation energy than the large, indicating that ECAP processing of Mg-Zn-Nd alloy superplastic deformation mechanism of grain boundary diffusion should be controlled by grain boundary sliding.

3 Conclusion
(1) Analysis of flow stress and strain rate can be drawn, after post-ECAP Mg-Zn-Nd alloy of four times the elongation of C best.

(2) The relationship between flow stress obtained with the experimental temperature, after post-ECAP Mg-Zn-Nd alloy superplastic deformation mechanism of grain boundary diffusion should be controlled by grain boundary sliding.

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