Effect of cold rolling and short-term annealing on microstructure and hardness of A356 aluminum alloy

In this research, the effect of cold rolling and short-term heat treatment on the microstructure and hardness of A356 aluminum alloy were investigated. Microstructural observations by optical microscopy, quantitative analysis using Clemex software and hardness test by Brinell macrohardness were performed. The results showed that the rolling process led to refining, increasing the sphericity, and decreasing the aspect ratio of the silicon particles, as well as removal of porosity in the casting sample. The distribution of silicon particles at the RD-ND plane was more uniform than the RD-TD and section because during the rolling process, the dimensional changes occurs only in the RD and ND directions, resulting in more plastic deformation at the RD-ND plane, and the distribution of silicon particles which is totally dependent on the amount of plastic deformation became more uniform. Also, rolling and heat treatment caused the grain refinement of aluminum through activation of continuous recrystallization and particle stimulated nucleation (PSN) mechanisms. The presence of silicon particles resulted in formation of finer grains and also suppression of the grain growth. Rolling process increased the hardness of the sample, but the heat treatment up to 300 s reduced the hardness. Finally, increasing the heat treatment time to 600 s resulted in an increase in hardness of 26% due to the completion of the continuous recrystallization mechanism.