| JIA Zheng,YU Bing,FU Li,LE Qi-chi.Effect of Zn on Corrosion Resistance of Extruded Mg-3Sn-1Ca Alloy[J],52(4):233-242 |
| Effect of Zn on Corrosion Resistance of Extruded Mg-3Sn-1Ca Alloy |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.04.020 |
| KeyWord:Mg-3Sn-1Ca alloy Mg-3Sn-1Ca-1Zn alloy extrusion CaMgSn phase dynamic recrystallization corrosion resistance |
| Author | Institution |
| JIA Zheng |
College of Mechanical Engineering, Shenyang University, Shenyang , China |
| YU Bing |
College of Mechanical Engineering, Shenyang University, Shenyang , China |
| FU Li |
College of Mechanical Engineering, Shenyang University, Shenyang , China |
| LE Qi-chi |
Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, Shenyang , China |
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| Abstract: |
| To improve the corrosion resistance of extruded Mg-3Sn-1Ca alloy. Two as-cast alloys Mg-3Sn-1Ca and Mg-3Sn-1Ca-1Zn were prepared by alloy melting using industrial pure Mg (99.9wt.%), pure Sn (99.9wt.%), Mg-25% Ca intermediate alloy and pure Zn (99.9wt.%). The as-cast alloy was homogenized (400 ℃×24 h). After homogenization, the ingot was processed into a 47 mm×100 mm casting blank with a diameter of 47 mm×100 mm by a lathe. The processed casting blank was preheated to 300 ℃ and put into a mold heated to 300 ℃. Reverse extrusion was carried out on a 300-ton vertical hydraulic press. After extrusion, the diameter of the bar is 12 mm. The microstructure and corrosion resistance of TX31 and TXZ311 alloys were analyzed by XRD, Metallography, SEM, EDS, EBSD, Hydrogen Evolution, Electrochemical Polarization Curve and Impedance Spectroscopy. The XRD and EDS results show that the second phase in the extruded TX31 and TXZ311 alloys is CaMgSn phase. Due to the addition of Zn, the CaMgSn phase increases and distributes more evenly in the TXZ311 alloy. The Metallographic and EBSD results show that Zn addition can improve the dynamic recrystallization degree of the TX31 alloy and the texture strength of {0001} base plane, and improve the microstructure heterogeneity of the TX31 alloy. From the polarization curve, the corrosion potential and corrosion current are ‒1.57 V and 6.95×10‒5A respectively. After Zn was added, the corrosion potential increased (‒1.49 V) and the corrosion current decreased (1.02×10‒5A), indicating that the corrosion resistance of the alloy was improved. By comparing the impedance spectra of the two alloys, it can be found that the TXZ311 alloy has a larger capacitive arc resistance than TX31 alloy, indicating that the charge transfer resistance on the surface and the resistance of the surface film are the highest, and the oxidation product film has a good stability during the dynamic corrosion process, which effectively prevents the corrosion of α-Mg matrix. The amount of hydrogen evolution of the TX31 alloy is proportional to time, and the corrosion rate is 3.7 mm/a. However, the corrosion rate of the TXZ311 alloy is only 1.6 mm/a, and the amount of hydrogen evolution decreases significantly after 12 h corrosion, indicating that an oxide film is formed on the surface of the alloy which can hinder the corrosion process. Zn element can greatly improve the corrosion resistance of the TX31 alloy. This is because after the addition of Zn element, the TXZ311 alloy dynamic recrystallization degree is higher, the structure is more uniform, so that the grain boundary and phase boundary are strengthened, inhibit the hydrogen evolution reaction of the cathode, and thus hinder the dissolution of the anode. Secondly, compared with the TX31 alloy with serious local corrosion, the corrosion film formed during the corrosion of the TXZ311 alloy has good adhesion, covers the alloy surface well, and effectively delays the corrosion of magnesium matrix. In addition, the texture also has a great influence on the corrosion resistance of the alloy. Studies have shown that the deformed magnesium alloy can increase the strength of the texture on the base plane and thus improve the corrosion resistance of the alloy, which is due to the higher atomic density and higher activation energy of the base plane. In this paper, the texture strength of TX31 alloy {0001} base plane is 7.29, and the addition of Zn element makes the texture strength of {0001} base plane reach 16.6, which makes a certain contribution to improve the corrosion resistance of the alloy. Therefore, the TXZ311 alloy corrosion resistance is much higher than the TX31 alloy. |
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