402 ISSN 0031-918X, Physics of Metals and Metallography, 2019, Vol. 120, No. 4, pp. 402–409. © Pleiades Publishing, Ltd., 2019. Published in Russian in Fizika Metallov i Metallovedenie, 2019, Vol. 120, No. 4, pp. 433–441. Influence of Rare Earths Addition on the Properties of Al–Li Alloys S. Nazarov a , S. Rossi b , P. Bison b , I. Ganiev a , L. Pezzato c , and I. Calliari c, * a Technological University of Tajikistan, Dushanbe, 734061 Republic of Tajikistan b CNR-ITC, Padova, 35127 Italy c Department of Industrial Engineering, University of Padova, Padova, 35131 Italy *e-mail: irene.calliari@unipd.it Received February 12, 2018; revised October 15, 2018; accepted November 12, 2018 Abstract—Aluminum alloys are considered one of the best choices as structural material for aerospace appli- cations, guaranteeing lightweight and strength at the same time. In this work Al–Li alloys with 6% (wt %) of Li are used. To increase further the strength of the material, new alloys are produced by adding different quantities (0.01, 0.05, 0.1, and 0.5 wt %) of rare earths (Nd, Y, Ce, Pr). The microstructure of the samples is examined using scanning electron microscope (SEM). The improvement of the mechanical properties is measured by means of Vickers hardness tests. Also the corrosion resistance of the alloys is evaluated with open circuit voltage (OCV) measurements. At the same time, the thermophysical properties are measured as well, at various temperatures, from 80 to 500°C. The results show that an increase in the Rare Earth (RE) content causes an increase in the mechanical properties and a reduction in the thermal conductivity. Regarding the corrosion resistance, a maximum in the corrosion properties can be found for 0.05% of RE. Keywords: IR thermography, thermophysical properties, anisotropy evaluation, hardness, corrosion DOI: 10.1134/S0031918X19040094 INTRODUCTION The last decade is characterized by the rapid expansion of the range of new materials as plastics and composites; however, metals and alloys still remain the main structural materials in the manufacture of machinery, equipment, appliances, building con- struction, transportation, and communications. In this regard, the improvement of methods to increase corrosion and mechanical properties is important not only for the possibility of reducing the economic loss, but also to provide further technical progress. The progress in new aerospace structures that demand improved damage tolerance and weight effi- ciency leads to the development of a number of inter- esting alloys. Therefore, the research on Al–Li alloys has attracted worldwide attention [1, 2]. Aluminum-lithium alloys are a new class of well- known aluminum systems and are characterized by a perfect combination of mechanical properties: low density, high elasticity modulus, and a sufficiently high strength. The increased interest in the alloying aluminum with lithium, the lightest metal with a den- sity of ∼0.54 g/cm 3 , is because each percent of lithium lowers the density of aluminum of 3% and increases the Young modulus of about 6%. Lithium is non-toxic and has desirable precipitation hardening characteris- tics. The Al–Li alloys have strong anisotropy in mechanical properties and poor ductility. A possible mechanism responsible for the Al–Li alloys embrittle- ment is their high sensitivity to deleterious impurities. The use of advanced vacuum methods and the addi- tion of rare earths can be beneficial. The vacuum pro- cess reduces the level of impurities, whereas the rare- earth elements can reduce the thermal conductivity and extend the ductility. It is well known that the addi- tion of rare earths to Al-based alloys improves tensile strength, heat resistance, vibration resistance, corro- sion resistance, and extrudability [3, 4]. This paper presents the results concerning the effects of rare earth (Ce, Y, Nd, and Pr) addition in the range 0.01–0.5 wt % on the microstructure and mechanical properties of cast Al + 6%Li. The interest in the thermophysical properties of such new alloys is related mainly to the thermal project of the aerospace structures. Furthermore, it is quite interesting to correlate the increased mechanical properties of the alloys, notably the hardness, with thermal conductivity that decreases as the hardness increases. It is therefore worth measuring thermal properties and their variation at increasing tempera- tures [5]. This is done for Al + 6%Li with and without the addition of 0.5% of rare earths (Y and Nd only for these tests). Finally, the anisotropy of thermal con- ductivity of such materials is measured by pulsed IR thermography technique [6, 7] along and perpendicu- larly to the direction of casting solidification. STRENGTH AND PLASTICITY