CORROSION-ELECTROCHEMICAL CHARACTERISTICS OF ALUMINUM ALLOY AlMg5.5Li2.1Zr0.15 (DURALUMIN) WITH LANTHANUM, CERIUM, AND PRASEODYMIUM ADDITIONS IN 0.3% NACL SOLUTION

The widespread use of duralumin in aviation, transportation and other industries is due to its high strength characteristics, low density and good manufacturability during casting and pressure treatment. The alloy under consideration belongs to the class of structural materials based on aluminum, reinforced with additives of copper, manganese, magnesium and lithium. Its operational properties are largely determined by the modes of heat treatment and the composition of the curing elements. One of the key factors limiting the durability of duralumin in aggressive environments is the tendency to local corrosion, in particular to pitting, which in freshwater is assessed primarily by the depth of damage. The results of a comprehensive study of the corrosion-electrochemical characteristics of an alloy of the AlMg5.5Li2.1Zr0.15 system (an analog of duralumin) additionally alloyed with small additives of rare-earth metals (lanthanum, cerium, and praseodymium) are presented. The experiments were performed in a model 0.3% NaCl solution using a potentiostatic technique in a dynamic mode at a polarization rate of 2 mV/s. The technique included recording the potential of free corrosion, constructing anode and cathode polarization curves, determining the potentials of pitting formation, and calculating the density of the corrosive current. It was found that an increase in the exposure time of the samples in the electrolyte, as well as an increase in the content of lanthanum, cerium, and praseodymium in the alloy, leads to a significant shift in the stationary corrosion potential to the positive region. The most pronounced effect was observed for praseodymium. At the same time, a decrease in the density of the corrosive current was noted. Modification of the alloy with rare earth elements contributed to an increase in its corrosion resistance in a chloride-containing environment by 10 ‒ 20 % compared with the base composition. The data obtained indicate that the introduction of La, Ce, and Pr leads to the formation of a more heterogeneous and passive surface that slows down the anodic processes of metal dissolution. The results of the work are of practical importance for the development of new corrosion-resistant aluminum alloys designed to work in conditions of exposure to seawater and other chloride-containing media.