The Effect of Casting-Defined Phase Composition on the Structural Transformation and Electro-Mechanical Properties in Al-Fe Alloy after Severe Plastic Deformation

Abstract

This paper studies the effect of the phase composition of cast Al-Fe alloy on its microstructure, properties and thermal stability after severe plastic deformation by high-pressure torsion (HPT). The aluminum alloy containing 1.7 wt. % Fe was produced by conventional casting (CC) and casting into electromagnetic mold (EMC), providing different phase composition, morphology and distribution in the initial state due to the different crystallization rate. In the CC alloy, the iron formed Al₁₃Fe₄ and Al₆Fe phases or particles, while in the EMC alloy, intermetallic particles have primarily Al₂Fe-alike composition. Such differences in size, distribution and composition of particles prior to HPT resulted in different levels of electro-mechanical properties in the deformed state. Both CC and EMC alloys demonstrate an increase in ultimate tensile strength (σ_UTS) and a decrease in electrical conductivity (EC) after HPT. The effects are more pronounced in the CC alloy, most likely due to the coarser particles. Annealing the samples after HPT at 230°C for 1h leads to a twofold decrease of the σ_UTS in the CC alloy and is accompanied by an increase in EC. At the same time, such heat treatment seemingly increased EC, decreased elongation to failure and had seemingly no effect on the σ_UTS of the EMC alloy. Overall, EMC alloy demonstrates higher thermal stability, most likely due to the presence and dispersion of the Al₂Fe intermetallic phase, which forms primarily due to the high cooling rate of the alloy, which is inherent in the EMC method.