Microstructure evolution of A380 aluminum alloy during rheological process under applied pressure

In squeeze casting process, the essence of mold-filling and feeding is rheological solidification of the alloy melt under pressure. Microstructure evolution is inevitable in this process, which affects the mold-filling and feeding in turn. In this work, the Archimedes spiral sample prepared by indirect squeeze casting was applied to investigate the microstructure evolution during the rheological process under pressure. The results showed that the primary α-Al phase was transformed from fine rosette-like or granular structure to coarse platelet-like structure with the increase of spiral length. However, the primary α-Al grain size of the starting point had a slight growing trend compared with that at the position of 140 mm away from the starting point. The volume fraction of the primary α-Al phase increased from 45.57% to 70.35% along the spiral length direction, demonstrating that the experimental pressure improved the rheological ability of the alloy melt to some extent. Furthermore, the eutectic Si phase was varied from a fine granular or wormlike structure to a coarse platelet-like or needle-like structure, and the dispersion of eutectic Si particles was also varied along the spiral length direction. This microstructure evolution was mainly owing to the comprehensive action of rheological solidification and pressurized solidification. More specifically, the microstructure evolution strongly depended on the pressure and rheological velocity during the rheological process, however, the effect of rheological distance was relatively small.