Effect of ultrasonic power on degassing and microstructure of large-scale 7085 aluminum alloy ingots

Abstract

In this work, five sets of large-scale 7085 Al alloy ingots (diameter 830 mm × length 3600 mm) were manufactured by introducing different ultrasonic powers (0–750 W) in the Direct-Chill (DC) casting process. The difference among the ultrasonic degassing, the α-Al grains, elemental segregation and eutectic phase with ultrasonic treatment were investigated. The results indicated that with the increase of ultrasonic power, the efficiency of ultrasonic degassing was gradually improved, which was decreased from 0.085 cm3/100 g to 0.056 cm3/100 g in ingot center part. The grain size was also dramatically refined, in which the grain refinement rate reached 38.2%, 42.8% with 550 W, 750 W power, respectively. The segregation of alloying elements (Zn, Mg, Cu) in the ingot was significantly suppressed, which the maximum positive deviations ∆C of Zn, Mg, and Cu were reduced by 59.5%, 55.9%, and 60.8%, respectively. In addition, the new Al14Cu2Fe3 (α−Fe) phase was the first to be discovered in the low power state and the coarse eutectic phase was more refined in the high power. The mechanisms of degassing, grain refinement and suppression of macroscopic segregation during ultrasonic casting were further revealed by calculating the acoustic energy density (I).