Project D5: Gradient structures
D3.1: Kinetic metallisation
•	Key researcher: N. Birbilis
Summary
Development of light alloys with structurally or chemically modified surfaces – or a combination of both structural and chemical modification. These alloys will have graded properties designed such that the surface behaves superior to the bulk for specific properties such as corrosion resistance. It is intended that this project will foster a strong link with Project D4, aimed at developing graded structures for the purpose of wear resistance.
Work to date includes:
•	Preparation of samples with modified (surface) structures induced by surface mechanical attrition, SMAT for Mg and Al; and by Equal Channel Angular Pressing (ECAP) for Mg.
•	Characterisation of SMATed and ECAPed samples to determine grain size.
•	Initial corrosion testing of Mg as a function of surface grain size with a view to understand this variable independently, and then proceed towards combining chemical modifications. The results for this work are seen in Figure D9. This work revealed that:
	-	Prior thermo-mechanical processing is a significant factor influencing corrosion properties of Mg through variation of its microstructural state.
	-	Grain size dependence of corrosion properties considered without regard of the processing methods used do not show any clear tendency. This demonstrates that the provenience of a particular grain structure is of crucial importance and that there are factors other than the grain size that control corrosion response.
	-	ECAP was demonstrated to significantly improve corrosion resistance. Specifically, the corrosion current was about two orders of magnitude lower than for the as-cast material. Thus ECAP offers itself as an attractive possibility of improving corrosion properties of Mg, while at the same time enhancing mechanical properties.
		Figure D11 - Corrosion rate (icorr) as a function of surface grain size for pure Mg