Influence of Ultrasonic Melt Treatment on Ni‐Containing Intermetallic Phases in Al–Si Piston Alloys

The influence of ultrasonic melt treatment (USMT) at different ultrasonic powers (0, 900, 2400, and 3000 W) on the morphology and chemical composition of Ni‐containing intermetallic phases (T‐Al₉FeNi and δ‐Al₃CuNi phases) in an Al‐11.5Si‐4Cu‐2Ni‐1Mg‐0.45Fe (wt%) piston alloy is investigated. The morphological characterization reveals that the USMT not only decrease the size of the T‐Al₉FeNi and δ‐Al₃CuNi phases but also change the morphology of T‐Al₉FeNi from skeleton‐ to block‐shaped. The block‐shaped T‐Al₉FeNi contributes the most to the high‐temperature properties because this morphology is beneficial in the formation of semi‐continuous network structures. The chemical composition of T and δ phases is analyzed. The Cu → Fe in the T phase and Ni ↔ Cu in the δ phase existing in the examined alloys are estimated. With increasing the ultrasonic power from 0 to 3000 W, the ultimate tensile strength, yield strength, and elongation are increased from 98.46 to 124.57 MPa, 82.4 to 101.87 MPa, and 2.95% to 5.12%, respectively, at 350 °C.