On the extrusion microstructural evolution of Al-Al₃Ni in situ composite

A directionally solidified Al-Al₃Ni in situ composite with fine Al₃Ni eutectic fibers was extruded at 200 and 400 °C. Evolution of the microstructures was then investigated by examining the partially and fully extruded portions of the billets. According to the results, extrusion at 200 °C will generate numerous tangled dislocations initially. When fiber breakage occurs, subgrains which are formed preferentially near the cracks will grow to eliminate the tangled dislocations and separate the pieces of broken fibers further apart, resulting in a fine subgrain structure with rod-like Al₃Ni particles distributed intergranularly. On the other hand, the billet extruded at 400 °C shows formation of large subgrains with many intragranular Al₃Ni fibers in the early stage. Upon further extrusion, the fibers are broken while the large subgrains are refined by forming dislocation bands and changing the bands to sub-boundaries. Consequently, the 400 °C-extruded billet shows fine subgrains with intergranular and intragranular rod-like Al₃Ni particles.