Effect of structural-phase transformations on the microhardness of the Al-22/oSi-3%Cu-1.7%Ni alloy after high-pressure torsion and annealing

The squeeze casting Al-22%Si-3%Cu-1.7%Ni alloy was subjected to high-pressure torsion (HPT) and subsequent annealing for investigation of their effect on the microstructure and microhardness. Specimens with a diameter of 8 mm and a thickness of 0.45 mm, cut from a squeeze cast ingot (region of ingot without primary silicon particles), were severely deformed by HPT via 5 revolutions under a pressure of 4 GPa at room temperature. The edge parts of the deformed samples were annealed at temperatures of 300, 400 and 500 degrees C for 5 minutes. HPT resulted in the refinement and partial dissolution of the eutectic silicon and primary intermetallic particles in an aluminum matrix with the formation of abnormal supersaturated solid solution and fragmentation of the structure that caused an increase in microhardness from 149 +/- 10 HV for the squeeze casting state to 285 +/- 14 HV for the deformed state. Subsequent annealing leads to the decomposition of the abnormal supersaturated solid solution, which occurred simultaneously with the recovery and recrystallization of the fragmented structure, which led to a decrease in the microhardness to 183 +/- 5, 108 +/- 5 and 132 +/- 6 HV at temperatures of 300, 400 and 500 degrees C, respectively.