Precipitation behavior of spray-formed aluminum alloy 7055 during high temperature aging

The precipitation behavior of spray-formed aluminum alloy 7055 during high temperature aging at 360-440 degrees C was studied by using scanning electron microscopy and transmission electron microscopy, together with hard-ness and electrical conductivity measurements. The nucleation, growth and dissolution mechanism of eta phase were analyzed based on precipitation thermodynamics. The results show that the main precipitates of the alloy during high temperature aging is eta phase. At the initial rapid heating-up stage, the nucleation is dominant to influence the size and number density of eta phase; during the subsequent isothermal aging, the growth rate has a dominant effect on eta phase. The existence of eta phase is related to its critical size at a given temperature. For the spray-formed aluminum alloy 7055, a most suitable high temperature aging treatment is 400 degrees C for 2 min. In this condition, the alloy forms more eta phases in finer sizes, and its precipitation free zone around grain boundaries becomes narrower. Such microstructure is benefited from the balance of nucleation and growth of eta phase, which in turn improves the hardness and conductivity of this alloy.

Automated summary

The precipitation behavior of spray-formed aluminum alloy 7055 during high temperature aging was studied, and the results showed that eta phase was the main precipitate. The most suitable aging treatment was found to be 400 degrees C for 2 minutes, which resulted in the formation of finer eta phases and improved hardness and conductivity.