**1. Introduction**

For many years, electrical engineering applications have been recognized as one of the main uses of aluminum in terms of industry economics, which is constantly developing under the current widespread tendency for replacing copper conductors [1]. Most conductive Al alloys are related to 1xxx (Al-Fe-Si), 6xxx (Al-Mg-Si) and 8xxx (Al-Fe) families. For manufacturing electrical parts with appropriate parameters, continuous casting and rolling are currently used for shaping and deformation strengthening. However, the latter is highly reduced after heating to above ~250 ◦C due to recrystallization.

For the sake of both improving heat resistance and operating temperature, Al-Zr alloys have been developed for particular applications, like overhead cables for long-distance

**Citation:** Belov, N.; Akopyan, T.; Korotkova, N.; Murashkin, M.; Timofeev, V.; Fortuna, A. Structure and Properties of Ca and Zr Containing Heat Resistant Wire Aluminum Alloy Manufactured by Electromagnetic Casting. *Metals* **2021**, *11*, 236. https://doi.org/10.3390/ met11020236

Academic Editor: Qudong Wang

Received: 20 December 2020 Accepted: 26 January 2021 Published: 1 February 2021

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power transmission [2–7]. Transition element Zr provides a far higher recrystallization temperature (up to 400 ◦C) due to the formation of the nanoscale metastable Al3Zr phase with a L12 crystal lattice [8–13] while heating to above 350 ◦C and decay of solid solution (Al) [14–19]. However, if not controlling the foregoing parameters of melting and casting, the unfavorable Al3Zr phase with a D023 structure may appear. According to the binary Al-Zr diagram [6], the liquidus temperature rises dramatically with Zr, hence, the temperature of the melt must be considered depending on the concentration. Additionally, for achieving metastable solubility, a relatively high cooling rate must be provided. The latter may be achieved by techniques like electromagnetic casting (EMC) that is superior to direct chill casting (DC). EMC allows producing long rod billets with far higher surface quality and an exceptionally fine microstructure due to support of the liquid pool by electromagnetic forces, continuous stirring, and increased cooling rates up to 10<sup>4</sup> K/s [20]. Based on the cooling rates, close to rapid solidification techniques [1,21], it may be argued that EMC is a very appropriate method for obtaining high-solute alloys, include those alloyed with transition elements. It was recently demonstrated [22] that Al alloy containing 0.6% Zr, 0.4% Fe and 0.4% Si (wt.%) may be successfully manufactured by EMC to long-length 12 mm circular cross-section rods with a microstructure containing Zr-rich solid solution. This structure provided excellent processability in cold drawing down to 3 mm, and the wire product showed a remarkable combination of strength (ultimate tensile strength (UTS) ~230 MPa) and electrical conductivity (55.6% IACS), both remaining stable after heating up to 400 ◦C.

In addition to Fe and Si used, subsequent development can be considered in alloying by rare-earth metal (REM) [21,23] and calcium [24,25]. They are both recognized to be very efficient for improving the heat resistance of Al alloys. However, while rare earth metals (REM) are more established for Al alloys, unconventional calcium may bring far higher cost efficiency combined with favoring the physical and mechanical properties. Particularly, it was shown that the Al wire alloy containing Al-4% Ca-1% Fe-0.6% Si-0.2% Zr-0.1% Sc manufactured from DC cast 150 mm billet has an improved combination of properties compared with Al–REM alloys [24]. This is due to its structure combining an Al matrix strengthened by Al3(Zr,Sc)-L12 phase particles and uniformly distributed submicron particles of Ca-bearing phases. Simulation of DC casting and flat rolling for the Al-0.5% Ca-0.5% Fe-0.25% Si-0.2% Zr-0.1% Sc alloy also showed the possibility for achieving such a combination of basic characteristics [25]. In respect to the foregoing compositions, scandium alloying may bring excessive costs of products. Using EMC technology, it is possible to introduce up to 0.6% Zr, that can be as efficient as the combination of Zr and Sc. Hence, we find it expedient to consider the Al–Ca–Zr–Fe–Si system as the base one. According to our earlier results [5,22,24–26], the target structure can be achieved in the alloy containing ~1% Ca, 0.5% Zr, 0.5% Fe, 0.25% Si (wt.%). Based on above, the goal of the present work is to study the structure, mechanical properties and electrical conductivity of the aluminum wire alloy of the foregoing composition manufactured by direct cold drawing from an as-cast 12 mm circular cross-section EMC rod and subjected to various heat treatment routes.
