The wide availability of the light alloys aluminium, magnesium and titanium, has been critical to modern engineering, in particular where high specific strength and stiffness is required. Aerospace is the classical application, and in 100 years of powered flight light alloys are the most extensively used materials. Metallurgy of light alloys has advanced from simple craft and intuition, in the early 20th century, to the current position of fundamental understanding of the physical principles of alloys at the macro and microstructural level. Despite decades of research there are still many areas of uncertainty, in particular at the atomic scale, regarding the structure of fine precipitate phases and the details of nucleation, growth and coarsening that drive the development of properties. At these length scales characterisation techniques struggle to overcome the limitations imposed by instrumentation, in terms of resolution and sensitivity, and the specimen itself, such as large lattice strains and in particular the small number of atoms involved in solid state phase transformations. Here the opportunities provided by the aberration corrected scanning transmission electron microscopy (STEM), combined with image simulation and ab initio calculation, to long standing problems in light alloy atomic structure and phase transformations will be explored. To illustrate this examples results will be presented from studies of precipitates in a selection of light alloy systems; these include the Al-Cu-x Guinier-Preston system [1], Mg- rare earth (RE) alloys [2,3] and ultra-high strength Al-Cu-Li alloys. [4]
References:
[1] L Bourgeois et al, PRL 111, Art. No. 046012
[2] Z Xu, M Weyland and JF Nie, Acta. Mat. 81, p. 58.
[3] Y Zhu et al Scripta. Mat. 81, p. 58.
[4] The authors acknowledge funding from the Australian Research Council grants no LE0454166 and DP0346745, and access to the Monash Sun Grid and national Computing Infrastructure facility.