Influence of processing temperature and die angle on the grain microstructure produced by severe deformation of an Al-7% Si alloy

Severe plastic deformation by equal-channel angular pressing has been carried out to high strains by repeated pressing using both a high-strain die and a moderate-strain die at both room temperature and at intermediate temperature. The die used appears to play no role in determining the saturation grain and dislocation microstructure after very high strains, with similar submicron grains, high dislocation densities, and silicon particle refinement observed. A slight tendency to microstructural non-uniformity is seen with the high-strain die. Severe plastic deformation at intermediate temperature leads to a coarser grain size, lower dislocation density, and precipitation of silicon from solution. The extent of grain coarsening, dislocation recovery and precipitate growth is much greater than when annealing room-temperature deformed material, since the high dislocation density accelerates precipitate formation and growth. Material strength is well described by the respective contributions of grain boundaries, dislocations, and precipitates.