Assessment of intermetallic compound formation during solidification of Al–Si piston alloys through thermal analysis technique

Multicomponent Al–Si–Ni–Cu–Mg alloys are widely used as automotive piston materials. The aim of the present work is to study the complicated formation of different intermetallic compounds during the solidification of two types of piston alloys: LM13 alloy with 0·9Ni–0·9Cu–1Mg and 3HA alloy containing 2·6Ni–3Cu–0·2Mg. Solidification events were detected by three-thermocouple thermal analysis technique, and microstructure evaluations were carried out using optical microscopy, scanning electron microscopy, energy dispersive X-ray analysis and quantitative image analysis. In addition to the (Al)+(Si) eutectic reaction, the results show a complicated precipitation of different post-eutectic phases, the most important of which are Al₉FeNi, Al₃Ni, Al₃CuNi and Mg₂Si. Ni rich Al₉FeNi and Al₃Ni phases have the highest formation temperatures among other intermetallics, which are detected in the range of 553–558°C in 3HA alloy and 546–553°C in LM13 alloy.