Tuning the microstructure morphology and genetic mechanical properties of 2219 Al alloy with ultrasonic treatment

Abstract

Some defects i.e. dendrite, coarse eutectic phases, and serious macro-segregation were hard to eliminate when the ultra-large aluminum alloy was manufactured by conventional technique. An effective method with ultrasonic sonotrode was inserted into the direct-cooling casting system to manufacture the 2219 Al alloy billet (Φ1100 mm × 5400 mm), followed by multidirectional forging and solution-aging (MSA) treatment. A comparative study of the morphology of α-Al grains, eutectic phases, and precipitates, as well as the mechanical properties were investigated. The results indicated that more coarse eutectic networks agglomerated together in the center position compared with billet samples without ultrasonic treatment (NUT) and with ultrasonic treatment (UT). They were difficult to completely dissolve into the matrix in the downstream MSA process, and acted as preferential nucleation sites for micro-cracks, thereby decreasing the mechanical properties. The average grain sizes of billet were generally refined induced by UT. And a greater density of tinier, uniform distributed precipitates was obtained from the UT billet and MSA samples. The mechanical properties were obviously increased by ultrasonic treatment in the billet samples. Based on the present results and proposed hypotheses in previous works, the dominant mechanisms of UT on major microstructures and genetic effects on mechanical properties were discussed.