Improving the Strength and Ductility Balance of Al–Ca–(Fe, La, Ce) Ternary Eutectic Alloys by High-Pressure Torsion Processing and Subsequent Annealing

Abstract

New ternary eutectic aluminum alloys, namely Al–6Ca–3Ce, Al–6Ca–3La, and Al–6Ca–1Fe (wt%) were studied in as-cast state as well as after the high-pressure torsion (HPT) processing and subsequent annealing. It was found that HPT (3 revolutions) formed a nanocrystalline grain/subgrain microstructure or a mixed nano- and submicrocrystalline grain/subgrain microstructure. Moreover, the numerous eutectic particles were refined down to the nanometer range, which led to the formation of multiple stress concentrators and embrittlement of the material. To improve ductility of the alloys, annealing treatment was used. It was shown that annealing at 350 °C (1 h) after HPT resulted in the multiple grain/subgrain growth and predominantly equiaxed grain microstructure formation in all alloys, as well as in the coarsening of some eutectic particles. This caused a decrease in stress concentration. As a result, the strength of the alloy increased and its ductility was restored. The ultimate tensile strength of the Al–6Ca–3Ce, Al–6Ca–3La, and Al–6Ca–1Fe alloys was 455, 422, and 377 MPa, respectively, which was 3.5, 2.2, and 2 times greater than in the as-cast alloys. The relative elongation of the Al–6Ca–3Ce, Al–6Ca–3La, and Al–6Ca–1Fe alloys was 2, 18, and 9%, respectively. Lanthanum, being part of the complex eutectic Al₄(Ca, La), ensured high ductility of the alloy, both in the cast state and in the deformed and heat-treated state.

Graphical Abstract