Effects of two-step homogenization on precipitation behavior of Al3Zr dispersoids and recrystallization resistance in 7150 aluminum alloy

The effect of two-step homogenization treatments on the precipitation behavior of Al3Zr dispersoids was investigated by transmission electron microscopy (TEM) in 7150 alloys. Two-step treatments with the first step in the temperature range of 300-400 °C followed by the second step at 470 °C were applied during homogenization. Compared with the conventional one-step homogenization, both a finer particle size and a higher number density of Al3Zr dispersoids were obtained with two-step homogenization treatments. The most effective dispersoid distribution was attained using the first step held at 300 °C. In addition, the two-step homogenization minimized the precipitate free zones and greatly increased the number density of dispersoids near dendrite grain boundaries. The effect of two-step homogenization on recrystallization resistance of 7150 alloys with different Zr contents was quantitatively analyzed using the electron backscattered diffraction (EBSD) technique. It was found that the improved dispersoid distribution through the two-step treatment can effectively inhibit the recrystallization process during the post-deformation annealing for 7150 alloys containing 0.04-0.09 wt.% Zr, resulting in a remarkable reduction of the volume fraction and grain size of recrystallization grains.