Abstrakt
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 degrees C and form shells surrounding Al3Sc particles.
This process is not affected by dislocations. The maximum fraction of positrons annihilated by Sc and Zr electrons occurred at 300 degrees C, coinciding with hardening of the alloy.
The resistivity changes above 300 degrees C are caused by precipitation of Mn-containing particles.