Thermal behaviour and microstructure evolution of new ternary eutectic alloy in Al-Cu-Si-Ni system

Abstract

Copyright © 2023 The Author(s). Eutectic alloys were fabricated from the quaternary Al-Cu-Si-Ni system via arc melting and suction casting. An invariant ternary eutectic reaction (α-Al+Si+θ-Al2(CuNi)) was found in the quaternary alloy system with a composition of Al67.2Cu24Si8Ni0.8 (wt.%). The dissolution of Ni (~1.7 at.%) into tetragonal θ-Al2Cu takes place during this ternary eutectic reaction. Density functional theory (DFT) calculations show that the configurational entropy stabilises this level of randomly substituted Ni with Cu sites in the θ-Al2Cu lattice at high temperatures. The as-solidified eutectic microstructure exhibits a lamellar θ-Al2(CuNi) phase showing fragmented lamellar morphology with a lamellar thickness of 130±30 nm and Si exhibits fibrous morphology with a fibre diameter below 100 nm. The thermal stability of the Al-Cu-Si-Ni eutectic alloy after post-solidification annealing was investigated, and the thermal stability of the ternary eutectic microstructure is better than the corresponding Al33Cu (wt.%) binary eutectic microstructure. It was found that Ni solution in θ-Al2(CuNi) phase contributes to the thermal stability of this ternary eutectic microstructure and β2-Al3(CuNi)2 (β1-(Cu2.9Ni0.1)Al type, Fm-3m) phase can transform from θ-Al2(CuNi) phase after annealing at different temperatures. The Al-Cu-Si-Ni eutectic alloy has excellent as-cast hardness together with thermal stability. It is potentially valuable for the design of new aluminium alloys for serving at elevated temperatures.