Superimposed dispersoid and precipitation hardening of AlMnMgSi wrought alloys

Process chains of AlMnMgSi wrought alloys comprise casting, homogenisation, hot forming and age hardening, which includes solution annealing, quenching, and ageing. These steps are typically carried out discontinuously with intermediate cooling and reheating. Relative coarse dispersoid formation through homogenisation with the main objective, to prevent grain growth during further processing of wrought aluminium alloys has been used since decades. But the objective of this study, to form finer dispersoids with an own strengthening contribution and superimpose this effect by age hardening has not been investigated yet. Homogenisation parameters were adjusted to precipitate a large number of fine dispersoids, which should contribute to strengthening. They should be retained throughout the subsequent process chain, including extrusion, solution annealing and artificial ageing. Different process chains were carried out with various integrative combinations of homogenisation, extrusion and solution annealing. Hardness tests were performed to evaluate the age-hardening behaviour and tensile tests were carried out to assess the mechanical properties. Transmission electron microscopy (TEM) was used to characterise the morphology and distribution of the dispersoids and to investigate how they are influenced by the further process chain. The results demonstrate that, by adjusting the process chain, the number of process steps could be reduced, while maintaining the same level of hardness and tensile properties. The TEM observations clearly showed a strong dependence of the coarsening and number of dispersoids on solution annealing parameters. An additional alloying of 0.2 wt% Zr led to the precipitation of Zr-containing dispersoids, which contributed to a further increase in hardness.