Ductile aluminium and brittle trialuminides

Abstract

The ductility of aluminium is attributed to the low elastic shear modulus of this fcc metal. Its trivalency endows a strong electrostatic resistance to shear, but this is almost entirely offset by a negative band structure contribution, due to a special Brillouin zone feature, with the result that the C44 shear component is very small. Several effects are associated with the addition of transition metals, for example in trialuminides such as Al3Ti. Outstandingly, the band structure contribution is severely reduced, because the large scattering cross-sections of the transition metal atoms greatly reduce the Brillouin zone effect. As a result, C44 becomes large and the alloyed crystal is thereby embrittled. Because similar scattering occurs in dilute random solutions of transition metals in aluminium, there is a direct link between electrical resistivity and brittleness in these materials.MST/1527