Effects of homogenization treatment on the microstructures of 5052-Er Al alloy

Abstract:

The effects of single-step, two-step and three-step homogenization treatments on the microstructures of 5052-Er Al alloy were studied by optical microscopy, scanning electron microscopy and transmission electron microscopy. The results showed that after 560℃/30h high temperature homogenization treatment, most of the non-equilibrium eutectic phases existed in the as-cast alloy dissolved, with the remaining phases being Fe-rich phases like Al₃Fe and Al-Fe-Er. The second step treatment performing at lower temperature was found to be beneficial to the spherization and refinement of the Fe-rich phases. The results also showed that homogenization treatment regimes had an obvious effect on the precipitation behavior of the fine precipitates. During the slow cooling process from 560℃/30h isothermally holding to room temperature, there were a large amount of rod β’(Al₃Mg₂) and spherical Al₃(Er, Zr) and Al₃Zr phases precipitating out of the matrix. The total volume fraction of the precipitates, 7.4%, was the highest among the four regimes conducted in this experiment. However, these precipitates distributed unevenly and their sizes differed greatly with each other. The second step treatment favored the formation of fine and homogenously distributed precipitates of Al₃(Er, Zr) and Al₃Zr. When the second step treatment was carried out at 150℃, the quantity density of the precipitates was the highest (20.3um_-1) with the finest particle size(average radius being 14nm). Three-step homogenization treatment could obtain a higher quantity density while maintaining a comparable particle size with that in two-step treatment.

Key words:5052-Er aluminium alloy; homogenization treatment; microstructure; precipitates