Electrodeposition Of Al-Mn-Zr Ternary Alloy Films In Ionic Liquids And Their Electrochemical Corrosion Performance

Aluminium and its alloys exhibit excellent physicochemical properties. Especially, Al-Mn binary alloy not only has good formability and decorative features, but also shows high strength and good corrosion resistance. Recently, Al-Mn binary alloys with metallic glass structure have aroused great interest. However, the Al-Mn binary alloys with low manganese content can not provide good corrosion protection for metal substrates because of their coarse grains and large voids between different particles. Ionic liquid has attracted enormous attention owing to their low melting point, extremely low vapor pressure, high thermal stability and wide eletrochemical window.In order to improve the corrosion resistance of Al-Mn binary alloys with low manganese content, Al-Mn-Zr ternary alloy films are deposited on low carbon steel substrate by electrodeposition in the ZrCl4-containing AlCl3-MnCl2-EMIC (1-ethyl-3-methy- limidazolium chloride) ionic liquids. The electrodepositions of Al-Mn-Zr ternary alloy fims are examined by linear sweep voltammetry (LSV) and chronopotentiometry. The morphology, composition, crystal structure and electrochemical corrosion performance of the resulting Al-Mn-Zr ternary alloys are investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), polarization curves and electrochemical impedance spectroscopy (EIS). The main results are as follows:(1) The results of linear sweep voltammetry and chronopotentiometry show that the addition of ZrCl4 increases the overpotential of electrodeposition, promoting the nucleation of electrocrystallization. Consequently, crystals of the coating can be fined.(2) The effects of the concentration of ZrCl4 on the morphology, structure, elemental composition and distribution of the coatings are studied. The results show that the grains of Al-Mn-Zr ternary alloy films with low Zr content are much more finer compared with the grains of Al-Mn alloys, however, the grains still remain micro-scale and Zr, Mn exist in the form of saturated solid solution. A denser coating composed of nanoscale particles (50 nm) is successfully obtained in the AlCl3-MnCl2-EMIC ionic liquid containing 5 mM ZrCl4. In addition, the coating is a mixture of crystalline and amorphous structures. When the amount of the ZrCl4 reaches 10 mM, particle aggregation occurs, and finally results in a loose deposition layer. The results of EDS, XRD and Mapping tests indicate that Al-Mn-Zr ternary alloy films is successfully codeposited and Al, Mn, Zr are all evenly distributed on the surface of the coating.(3) The results of corrosion tests reveal that Al-Mn-Zr ternary alloys show higher corrosion resistance compared with Al-Mn binary alloy, indicating that the addition of Zr gives a favorable improvement in anticorrosion performance of Al-Mn binary alloys. The Al-Mn-Zr ternary alloy film electrodeposited from ionic liquid with 5 mM ZrCl4 shows a perfect corrosion resistance performance.