Effects of equal channel angular pressing and further cold upsetting process to the kinetics of precipitation during aging of 7050 aluminum alloy

Abstract

The effect of equal channel angular pressing (ECAP) and further cold upsetting (CU) process on the kinetics of precipitation during aging of solid solution treated 7050 Al alloy were studied using differential scanning calorimetry and transmission electron microscopy. Results indicate that the activation energy of η′ phase was reduced from 120.371 kJ/mol to 73.387 kJ/mol after ECAP process and to 59.740 kJ/mol after CU process, because of the accumulation of dislocations. Thus, the peak aging time was shortened from 333 h to 7 h and 3 h after ECAP and ECAP−CU composite process respectively. Additionally, the precipitation of the η phase was suppressed after ECAP, but accelerated after ECAP−CU process, with the change of activation energy from 185.323 kJ/mol to 208.266 kJ/mol and 156.060 kJ/mol respectively. The annihilation of dislocations and precipitation of phases during aging treatment led to the competition of softening and strengthening of mechanical strength, indicating that the increasement of elongation is coupled with slight reduction of strength. After peak aging treatment, the tensile strength remained approximately unchanged of 546 ± 14 MPa, while the uniform elongation increased by about 35.3% from 5.1 ± 0.6 to 6.9 ± 1.5.