Homogenization Annealing Process Optimization of Extruded 7B04 Aluminum Alloy

The extruded 7B04 aluminum alloy was subjected to single stage homogenization annealing (annealing temperature of 450–490 ℃, annealing time of 4–36 h) and double stage homogenization annealing (the second stage homogenization annealing process of 480 ℃×4 h/10 h or 495 ℃×4 h/10 h) based on the optimized single stage homogenization annealing. The effects of annealing temperature and time of the two processes on the phase composition, microstructure, and hardness of the alloy were studied. The optimal homogenization annealing process was obtained.The results show that after the single stage homogenization annealing with the increase of annealing temperature, the area fraction of the second phase, such as MgZn₂ and Al₂MgCu, first decreased and then increased, and the hardness first increased and then decreased; with the extension of annealing time, the area fraction of the second phase decreased, and the hardness first increased and then decreased. The optimal process of single stage homogenization annealing was annealing temperature of 460 ℃ and annealing time of 24 h, and at this time a large number of the second phase was redissolved, and no overburning and grain growth occurred in the structure, and the hardness of the alloy was the highest. Under the double stage homogenization annealing process, after the second stage homogenization annealing of 480 ℃×4 h/10 h, the second phase of the aluminum alloy was further redissolved, and the microstructure did not overburn; the area fraction of the second phase under the annealing time of 10 h was lower, and the hardness of the alloy was higher. When the second stage homogenization annealing temperature increased to 495 ℃, overburning of the aluminum alloy occurred. The optimal double stage homogenization annealing process for the extruded 7B04 aluminum alloy was 460 ℃×24 h+480 ℃×10 h. At this time, the second phase was basically dissolved, and only a small amount of spherical-like Al₂MgCu phase with size about 1 µm existed.