Author: Win Ken Look
Look, Win Ken, 2024 Design, development and characterisation of novel magnesium alloys with improved corrosion resistance for medical applications, Flinders University, College of Science and Engineering
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Magnesium alloys have garnered significant attention in the biomedical field due to their potential as biodegradable implants that can reduce the need for secondary surgeries, however, their rapid corrosion remains a critical challenge. This thesis explores the development and characterisation of novel Mg-Zn-Zr-Y alloys to improve corrosion resistance and mechanical properties for biomedical applications. The research investigates six distinct alloy compositions in weight percentage (wt%): Alloy 1 (Mg-1Zn-0.5Zr-1Y), Alloy 2 (Mg-3Zn-0.5Zr-1Y), Alloy 3 (Mg-5Zn-0.5Zr-1Y), Alloy 4 (Mg-3Zn-0.25Zr-1Y), Alloy 5 (Mg-3Zn-0.75Zr-1Y), and Alloy 6 (Mg-3Zn-1Zr-1Y), focusing on their microstructural, mechanical, and electrochemical behaviours. The study began with selecting and formulating alloying elements based on extensive literature review and experimental design. Mg-Zn-Zr-Y alloys were synthesised and subjected to comprehensive characterisation using optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), tensile testing, Vickers hardness testing, electrochemical testing, and hydrogen evolution testing.
Microstructural analysis revealed significant grain refinement and uniform phase distribution in Alloy 2 (Mg-3Zn-0.5Zr-1Y), attributed to the synergistic effects of Zn, Zr, and Y. This alloy demonstrated the highest ultimate tensile strength (UTS) of 201.61 MPa, a yield strength of 80.72 MPa, and a Young's modulus of 39.41 GPa, coupled with good ductility at 11.78% elongation. Despite the variations in alloy composition, the hardness values ranged narrowly, with Alloy 2 showing a slightly lower hardness of 49.2 HV compared to other alloys. Corrosion resistance was determined using open circuit potential (OCP) measurements, potentiodynamic polarisation tests, hydrogen evolution testing, and SEM analysis of corroded samples. Alloy 2 exhibited a lower corrosion current density of 1.768 μA/cm² and the most positive OCP value of -1.521 V, indicating superior resistance to corrosion initiation and propagation. Additionally, it had the lowest hydrogen evolution rate of 0.017 ml·cm²·hr⁻¹ at the 10-hour period, further confirming its excellent corrosion resistance. The findings underscore Alloy 2's potential as a viable material for biomedical applications, combining superior mechanical performance with excellent corrosion resistance.
Keywords: Magnesium alloys, Corrosion resistance, Biomedical applications, Mechanical properties, Microstructural analysis, Corrosion behaviour evaluation
Subject: Engineering thesis
Thesis type: Masters
Completed: 2024
School: College of Science and Engineering
Supervisor: Reza Hashemi