Effect of lanthanum and cerium on cold workability of polycrystalline magnesium

The effect of lanthanum and cerium on cold workability of polycrystalline magnesium was investigated by means of hardness measurements, optical and transmission electron microscopy and examination of rolling textures obtained by Schulz's reflection method. The maximum cold rolling reduction without cracking increased with increasing concentration of lanthanum and cerium up to 0.2wt%. It was found that cerium was more effective than lanthanum to improve cold workability of magnesium. The deformation structure of an alloy containing 0.2wt% lanthanum or cerium at low reduction was much more uniform, and consequently compression bands developed afterwards were distributed more uniformly throughout the specimen, in comparison with pure magnesium and low concentration alloys. It appears reasonable to consider that the compression band observed in this work consists of a number of {1011} and {1015} twins. The feature of rolling texture was not altered by addition of lanthanum and cerium, however pole densities of {0002} and {1011} for the alloys were lower than those of pure magnesium at the same rolling reduction. At the final stage of deformation, cracks formed at the boundary region between the matrix and compression bands, and then propagated along the grain boundary.