Development of Mg-Al-Zn alloys with enhanced toughness and durability
thesisposted on 2017-03-01, 05:25 authored by Gusieva, Kateryna
In the present era of light weighting, magnesium (Mg) alloys are gaining popularity in many industrial applications, owing to a combination of low density and high specific strength. Whilst the low density of magnesium components is a significant advantage, the hexagonal crystal structure of Mg affects fundamental properties such as ductility and toughness. Adding controlled amounts of alloying additions such as Al, Zn, Mn, Y, Zr, Gd, Li, RE (rare earth blends, including one or more of Ce, Nd, La), produces Mg alloys with good specific strength, and, with further thermo-mechanical processing, it is possible to obtain even higher specific strength (comparable to that of other metal systems, such as steels). However, microstructural heterogeneities, brought about by alloying, often result in poor corrosion resistance. As such, to exploit the promise of Mg alloys, a balance of properties must be achieved. In spite of much recent research in this field, corrosion and mechanical properties are rarely studied together. Such a task is not trivial, however it is clear that to broaden the range of potential applications of Mg alloys, significant alloy engineering and design is still required – particularly to provide an optimised balance of mechanical and corrosion performance. The present work focuses on the optimisation, and related science, required to extend the property space of Mg alloy AZ31 using previously unexplored microalloying additions. In addition an in-depth investigation of the galvanic corrosion inherent to Mg alloys is carried out, using samples specially designed to provide macroscopic examples of galvanic corrosion. The findings reveal a new insight on the phenomenon of microgalvanic corrosion of Mg, that has not been previously reported – whereby the damage evolution is principally dictated by local pH.