Investigation on the homogenization annealing treatment of 5052-based aluminum alloys

Abstract

Proper homogenization annealing treatment of cast billet is essential to eliminate casting defects and improve the formability of Al alloys. In this work, homogenization annealing treatment in a wide temperature range from 475 to 590°C were conducted on 5052 and Er-modified 5052 Al alloys. The microstructure evolution with annealing temperature was investigated and the homogenized microstructures with and without Er addition were compared and analyzed. The results showed that the optimum homogenization treatment regime is ~560°C for 30 h for both alloys, although the Er-modified alloy can be heat-treated at relatively high temperature than 5052 base alloy. Er addition promotes the dissolution of Al₆Fe phase and helps eliminate the non-equilibrium casting structures. After homogenization, while the needle-liked Al-Fe intermetallic decreases its size from ~20 μm in the as-cast alloy to ~10 μm in the as-homogenized alloy with the stoichiometric ratio of Al to Fe being 4:1, the Al-Fe-Er ternary phase evolves to plate-like particles with the long axis only being ~ 1 μm. Moreover, Al-Zr-Er ternary granular particles, ~100 nm in diameter, were found to precipitate out from the matrix during the cooling process of the annealing treatment for the Er-containing alloy. It is also revealed that through proper annealing treatment, Er modification helps improve the formability of 5052 alloy.