| dc.description.abstract | This study investigated the effects of cold working before solution treatment (0%, 5%, 10%, 20%, 30%, 50%) on the microstructure and mechanical properties of AA7055-T76 high strength forged aluminum alloy, and improved AA7055-T76 High-strength aluminum alloy properties, by optical microscope (OM), conductivity measurement (% IACS), tensile test and Vickers hardness tester, etc. , to study the effect of alloy processing on microstructure and mechanical properties .
The results show that when the amount of cold working is larger, the number of texture structure increase, and the cold working amount of more than 30% produces a set of parallel shear bands, and at the 50% cold working amount, the second group appears. Also, the angle of the shear band to the rolling direction is gradually reduced. After heat treatment (T76), the processed alloy undergoes three stages of annealing, namely recovery, recrystallization & growth, and the degree of recrystallization increases as the amount of processing increases. The grain size after grain growth is inversely proportional to the amount of processing. In the case of a cold roll, the hardness gradually rises and the conductivity gradually decreases. After the solution treatment, the hardness and electrical conductivity recover to the state of not being cold worked. In addition, AA7055 aluminum alloy has fine and continuous precipitates on the grain boundary after T6 aging treatment, and the aging temperature is increased by T76 and T77. Thus, the precipitates on the grain boundary are coarse and discontinuous, and the precipitate free zone(PFZ) occur; due to the potential difference between the substrate and the precipitates, the discontinuous precipitates make T76 and T77 have better resistance to exfoliation corrosion(EXCO). The elongation of the T76 state also causes the precipitates in the grains to be coarse and the strength of the alloy to be lowered. The T77 state effectively returns the
strength to the peak aging due to re-aging.
Keywords: AA7055, cold roll, texture, recrystallization | en_US |