Evolution of Grain Boundary Phases during the Homogenization of AA7020 Aluminum Alloy

摘要

The presence of large constitutive particles formed during solidification decreases the strength and hot workability of aluminum alloys especially when they are located in the grain boundary (GB) regions. Therefore, the evolution of these phases is a major issue in the homogenization process of these alloys. There is a lack of information on the behavior of the GB phases during homogenization, which constitute more than 70 pct of all the secondary phases present in the microstructure of AA7020 aluminum alloys. The dominant GB phase is identified to be Al17(Fe3.2Mn0.8)Si2. In the present research, a comprehensive study on the effect of the homogenization treatment on the evolution of the GB phases during homogenization was conducted. The analysis shows that the evolution of this phase is largely dependent on temperature, which ranges from spheroidization with insignificant dissolution at low temperatures to full dissolution during homogenization at high temperatures. A new mechanism for the dissolution of these phases called thinning, discontinuation, and full dissolution (TDFD) is proposed based on the findings of the field emission gun–scanning electron microscope (FEG-SEM) analysis.