**Patrik Šulhánek 1, Marián Drienovský 1, Ivona Cerniˇ ˇ cková 1, Libor Duriška ˇ 1, Ramunas Skaudžius ¯ 2, Žaneta Gerhátová <sup>1</sup> and Marián Palcut 1,\***


Received: 20 June 2020; Accepted: 13 July 2020; Published: 15 July 2020

**Abstract:** In this work, the high temperature oxidation behavior of Al71Co29 and Al76Co24 alloys (concentration in at.%) is presented. The alloys were prepared by controlled arc-melting of Co and Al granules in high purity argon. The as-solidified alloys were found to consist of several different phases, including structurally complex m-Al13Co4 and Z-Al3Co phases. The high temperature oxidation behavior of the alloys was studied by simultaneous thermal analysis in flowing synthetic air at 773–1173 K. A protective Al2O3 scale was formed on the sample surface. A parabolic rate law was observed. The rate constants of the alloys have been found between 1.63 <sup>×</sup> 10−<sup>14</sup> and 8.83 <sup>×</sup> 10−<sup>12</sup> g cm−<sup>4</sup> s−1. The experimental activation energies of oxidation are 90 and 123 kJ mol−<sup>1</sup> for the Al71Co29 and Al76Co24 alloys, respectively. The oxidation mechanism of the Al-Co alloys is discussed and implications towards practical applications of these alloys at high temperatures are provided.

**Keywords:** Al alloy; Co alloy; complex intermetallic; oxidation kinetics; oxide scale
