INVESTIGATING THE CORROSION BEHAVIOUR OF ZX10 MAGNESIUM ALLOY IN VARIOUS CORROSIVE MEDIA AND THE CORROSION RESISTANCE OF MAGNESIUM OXIDE COATINGS

View/ Open
Date
2020-02-03Author
Xu, Zhen Z.X 1994-
ORCID
0000-0002-5467-6351Type
ThesisDegree Level
MastersMetadata
Show full item recordAbstract
At present, magnesium alloys are receiving considerable attention in the fields of computer parts,automotive,aerospace components, and biomedical applications because of their low density, high specific strength and bio-compatibility. Among them, the ZX10 magnesium alloy exhibits excellent mechanical properties. However, due to their poor corrosion resistance and insufficient mechanical properties when exposed to different aggressive environment, the engineering application of magnesium alloys is limited and requires appropriate surface treatment. This study, therefore, focused on the degradation behaviour of ZX10 magnesium alloy in different corrosive media at room temperature and the development of protective MgO coating on ZX10 magnesium alloy.
The degradation behaviour and corrosion rate of ZX10 magnesium alloy in different aggressive media with varying pH values, were investigated by employing the Tafel curve and electrochemical impedance techniques, and analyzed with the Scanning Electron Microscope (SEM). The chemistry and diffraction phases of adhering corrosion products were also investigated by utilizing the X-ray diffraction (XRD) technique. MgO coatings were electrodeposited on magnesium alloy using cathodic electrolytic method and subsequent calcination at different temperatures to improve the corrosion resistance. The protective performance of the MgO coatings was investigated by potentiodynamic polarization, and electrochemical impedance spectroscopy and a correlation was drawn between calcination temperature of coatings, corrosion resistance, and mechanical hardness. A modeled calcination mechanism, as it relates to barrier performance at low and high thermal conditions, has been
illustrated based on collected experimental evidence.
Results showed that magnesium alloy demonstrated varying rates of corrosion and passivation within a range of pH of corrosion media. The acidic systems showed the highest rate of metal corrosion while the lowest corrosion rate was observed for the alkaline systems. Localized corrosion has been observed by SEM, while electrochemical impedance spectroscopy and potentiodynamic polarization techniques reveal increased anodic polarization and charge transfer, respectively. The metal uniformly corroded for each examined corrodent over an extended period of time; however, the early corrosion stages reveal localized formation of oxide films at grain boundaries.
The protective MgO coating was successfully developed and optimized on ZX10 magnesium alloy. The internal tensile stress was produced in electrodeposition because of the occlusion of hydrogen atoms in the coatings. Results showed that at calcination temperature of 250 o C, the internal tensile stress was released leading to crystallization of oxide coating layers with compact
and continuous multi-layered micro-structures. At higher temperatures (around 500 o C), recrystallization of the MgO coating increased coating porosity and broadened inter-diffusion at micro-defects. Surface and bulk pores and cracks have been observed at 500 o C as clear evidence of the consequence of over-calcination. Enhanced corrosion resistance was observed for the MgO coatings obtained at 250 o C calcination temperature after chloride-induced corrosion tests and its corrosion current density is one thousand times smaller than that of bare magnesium alloy.
Degree
Master of Science (M.Sc.)Department
Mechanical EngineeringProgram
Mechanical EngineeringSupervisor
Szpunar, JerzyCommittee
Odeshi, Akindele; Cree, Duncan; Peng, Ding-YuCopyright Date
June 2020Subject
ZX10 magnesium alloy
corrosion behaviour
magnesium oxide coating
corrosion resistance.
Collections
Related items
Showing items related by title, author, creator and subject.
-
DETERMINATION OF THE SYNERGISM BETWEEN EROSION AND CORROSION IN POTASH-SAND SLURRY CORROSION OF CARBON STEEL
Trask, Michael Brent; 0000-0002-3765-6412 (2021-08-30)Erosion-corrosion is a common problem in the mining and mineral processing industries, both in Saskatchewan and other parts of the world. The combination of erosion and corrosion in flow systems may lead to severe material ... -
The effect of sensitization on the corrosion susceptibility and tensile properties of AA5083 aluminum
Adigun, Olusegun John (2006-02-09)Aluminum-magnesium alloy (AA5083-H116) is primarily designed for marine applications such as in ship hulls and deckhouses. Its excellent combination of physical and mechanical properties makes it useful for other applications ... -
Development of predictive models of flow induced and localized corrosion
Heppner, Kevin L (2006-05-05)Corrosion is a serious industrial concern. According to a cost of corrosion study released in 2002, the direct cost of corrosion is approximately $276 billion dollars in the United States – approximately 3.1% of their ...