Peculiarities of Structure and Phase Formation in the Surface Layers of 2024 Aluminium Alloy due to Ultrasonic Impact Treatment in Various Environments

Abstract

Îòòèñêè äîñòóïíû íåïîñðåäñòâåííî îò èçäàòåëÿ Ôîòîêîïèðîâàíèå ðàçðåøåíî òîëüêî â ñîîòâåòñòâèè ñ ëèöåíçèåé 2017 ÈÌÔ (Èíñòèòóò ìåòàëëîôèçèêè èì. Ã. Â. Êóðäþìîâà ÍÀÍ Óêðàèíû) Íàïå÷àòàíî â Óêðàèíå. 50 М. О. ВАСИЛЬЄВ, Б. М. МОРДЮК, С. І. СИДОРЕНКО та ін. Обговорено можливий механізм формування залiзовмiсного поверхневого шару за інтенсивної пластичної деформації та масоперенесення Fe, спричинених багатократним ударним навантаженням при УЗУО бойком з армко-заліза. Ключові слова: ультразвукове ударне оброблення (УЗУО), поверхня, масоперенесення, механічне леґування, алюмінієві стопи, інертне середовище. The hardening process of the surface layers of 2024 aluminium alloy caused by structural evolution and mass transfer of Fe induced by ultrasonic impact treatment (UIT) with the pin from Armco-Fe carried out in both the air and an inert environment is studied. The cyclical nature of changes in microhardness, which comprises the alternating stages of hardening and plasticization, is confirmed. The increase in the microhardness of the surface layers of 2024 aluminium alloy of  30 m thick after the UIT process with the pin from Armco-Fe in an inert environment (4 GPa) and in the air (up to  9 GPa) is associated with the decrease in the size of coherent scattering areas during severe plastic deformation and with the increase in crystal lattice microstrains, with mechanochemical interaction between Al and Fe with the formation of Fe-Al intermetallic phases as well as between Cu and O during UIT in the air. A possible mechanism for the formation of the iron-containing surface layer by severe plastic deformation and mass transfer of iron caused by repetitive impact loading at UIT with the pin of Armco-Fe is discussed.

Corrosion of 2024 alloy after ultrasonic impact cladding with iron

“…It decreases down to 6.6 GPa (FeAl) and 2.7 GPa (Fe 3 Al) with the increase of the iron content, which is still higher than the hardness of the 2024 alloy. Moreover, the prolonged air-UIT processing can induce failure of the formed oxides/intermetallics, and sequential occluding/trapping of the formed chips by the matrix alloy followed by intensive mechanical intermixing and formation of the layers of particle reinforced composite [16,22]. In our case, the layer formed after the air-UIT process (Figure 2(d)) is of a composite type.…”

“…Two series of specimens were processed either in the ambient air (air-UIT) or in the argon environment (argon-UIT). In the latter case, a special sealed chamber filled with gaseous argon was used to prevent the surface oxidation at UIT [16].…”

“…Mechano-chemical reactions enable the iron claddings owing to the combined plastic flow and interdiffusion at the interface (Figure 1(c)). Similarly to [15,16], a gradient microstructure is generated on the 2024 alloy by UIT, which contain the nanoscale grains (30-50 nm) on the top surface and submicronic/micron-size grains on the depth of ∼30-80 μm. Thus, the diffusivity of the component atoms is increased due to many structural defects and a lot of the transported atoms at the grain boundary.…”

“…Molybdenum [5] and NiAl [4,12] or FeCr [13] intermetallic claddings were produced by multiple ball collisions of the foil/substrate [5] and powder/substrate [4,12] sandwiches or substrate itself [13]. UIT induced mechanical alloying of the surface layers of 2024 alloy with iron using either plate [15] or pin [16] of Armco-iron served as a Fe source. The iron/intermetallic layers of various thickness, hardness, chemical and phase compositions were produced [15,16].…”

“…Some room temperature methods, such as friction stir processing (FSP) [1] and friction surfacing [11], ball impact cladding [4,5,12,13], mechanical alloying [8,9,14], and ultrasound impact treatment (UIT) [15,16], were used for joining dissimilar materials and producing intermetallics. FSP improved mechanical properties of aluminium owing to the formation of the Fe-Al surface nanocomposite contained nanoscale intermetallic particles and ultra-fine grained matrix [1].…”