Influence of dislocations on precipitation processes in hot-extruded Al–Mn–Sc–Zr alloy

Solute clustering and precipitation processes in hot-extruded Al–Mn–Sc–Zr alloy were studied. Positron annihilation studies were combined with electrical resistometry, microhardness testing and microstructural characterization. Extrusion introduced dislocations which arranged into a cell structure. Sc solutes segregated at dislocations. Moreover, fine coherent Al 3 (Sc,Zr) particles precipitated during extrusion and subsequent cooling. During the isochronal annealing Sc agglomerated forming Sc-rich dispersoids. Agglomeration of Sc solutes is facilitated by pipe diffusion along dislocations. Zr atoms become mobile above 240 °C and form shells surrounding Al 3 Sc particles. This process is not affected by dislocations. The maximum fraction of positrons annihilated by Sc and Zr electrons occurred at 300 °C, coinciding with hardening of the alloy. The resistivity changes above 300 °C are caused by precipitation of Mn-containing particles.