Behavior of dislocations and hardening mechanisms in Al-Li alloys.

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Abstract
Deformation induced substructures of aged Al-Li alloys containing coherent δ'-L12 ordered particles were studied by dark field transmission electron microscopy. Dislocations move as pairs when fine scale precipitation of δ'-particles occurs. The form and distance of pair dislocations strongly depends on the size and distribution of particles. Particles having the diameters less than apporoximatery 50nm can be sheared by dislocation pairs. When the particles grow larger, dislocations by-pass the particles leaving the dislocation loops around them. Basing upon the observed behavior of dislocations, strengthening mechanisms in the Al-Li alloys were discussed taking into account the various resistances to the dislocation movement in the alloys. Main contributions to the strength of the alloy come from the energy of antiphase boundary and the frictional stress in the ordered particles. The measured yield strength and observed arrangements of deformation induced dislocations well agree with the theoretical proposal.

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