Effect of Hot Pressing on the Microstructure and Hardness of ‎A390 ‎Cast Aluminum Alloy

In this research, the effect of the hot-pressing process on the microstructure and hardness of A390 cast aluminum-silicon alloy was investigated. The results were prepared using an optical microscope and hardness tester. The microstructure of the casting sample included very coarse primary silicones, acicular eutectic silicones, intermetallic compounds, and large alpha-phase dendrites. By increasing the amount of strain in the hot-pressing process, primary and eutectic silicones as well as intermetallic compounds were broken and finer, and their distribution in the alpha matrix became more uniform. The obtained results showed that the microstructure of the casting alloy has been improved in terms of the modification of primary silicon particles, eutectic silicon, and intermetallic compounds, as well as the uniform distribution of these particles and the removal of porosity. The initial silicon size is dramatically reduced from over 100 µm (for the cast sample) to less than 5 µm (after the seventh pass). By increasing the strain up to the fourth pass, the hardness of the alloy decreased from 87 to 65 HB. With the further increase of the strain from the fourth pass to the seventh (final) pass, the hardness value increased to 81 HB.