Deformation behaviour of Mg-Li-Al alloys

Two Mg-Li-Al alloys (LA43 and LA45) were deformed in compression at elevated temperatures. Stress relaxation tests were performed with the aim to reveal mechanism(s) of thermally activated process. Decrease of the c lattice parameter due to the Li addition results in the easier non-basal slip and reduces also the flow stress necessary for deformation of polycrystals and increases the ductility. Precipitates and solute atoms are expected to be the main obstacles for dislocation motion at lower temperatures. The dominant thermally activated mechanism at higher temperatures is very probably cross slip. The post relaxation effect (an increase of the stress after the stress relaxation test) was observed at room temperature for both alloys and also at 50degreesC for LA45. A local maximum observed in the temperature dependencies of the yield as well as the maximum stress and post relaxation effect indicate dynamic strain ageing. The strain ageing is due to migration of dissolved Li and Al atoms towards dislocations. (C) 2004 Elsevier B.V. All rights reserved.