The effect of the extrusion temperature and the extrusion ratio on the microstructure and mechanical properties of an Al-Li-Mg-Zr alloy in the as-extruded, solution-treated and aged conditions were investigated. It was found that an increase in the extrusion temperature and ratio increased the degree of recrystallization in the extrudate. An increase in the extrusion temperature also increased the sub-grain size, whereas the extrusion ratio did not affect the sub-grain size. The strength of the extrudates decreased and the ductility increased in the asextruded condition with increases in the extrusion temperature and the extrusion ratio.

Portevin-Le Chatelier (PLC) effect often occurs in many alloy systems and leads to flow stress variations. When precipitation occurs, the PLC behavior changes and its resultant influence on the flow stress becomes more complicated, which has not yet been clarified. The well-known interaction mechanisms between precipitates and dislocations are shearing (shearable precipitates) and bypassing (non-shearable precipitates). This study systematically investigates the influence of the PLC effect on the flow stress in three cases, namely, without precipitates, with shearable precipitates, and with non-shearable precipitates. This study is performed on a AlMgZrSc alloy, where the precipitation does not change the concentration of solute species that is responsible for PLC. A modified constitutive relationship considering different dislocation-precipitate interactions is proposed, which can quantify the contribution of the PLC effect to the flow stress in the above three cases. The modeling results agree well with those of experiments performed on AlMg and AlMgScZr alloys exhibiting the PLC effect. It is theoretically demonstrated that PLC-induced strengthening can account for as much as 14.5% of the total flow stress in AlMg alloys. When shearable and non-shearable precipitates appear, this percentage decreases to approximately 4.5% and 9.5%, respectively, indicating that the precipitates weaken PLC-induced strengthening. Moreover, shearable precipitates can shorten the strain rate range of PLC, which is more effective in suppressing the PLC effect than non-shearable precipitates. Finally, the intrinsic mechanism responsible for the PLC-induced strengthening and roles of different precipitate-dislocation interactions are discussed.