INFLUENCE OF SEVERE PLASTIC DEFORMATION ON THE STRUCTURE AND PHASE COMPOSITION OF ALUMINUM ALLOY 6061

10.25712/ASTU.1811-1416.2026.02.011

Abstract

In this work, the scanning electron microscopy, optical metallography and differential scanning calorimetry (DSC) methods were used to study the deformation-aging 6061 alloy (Al–Mg–Si–Cu). A rod made of 6061 with a diameter of 10 mm was obtained after hot pressing and severe plastic deformation by equal-channel angular pressing (ECAP) along the Bc route at 120 °C. The microstructure and phase composition, as well as the size and shape of phases and their distribution in alloy after hot pressing, heat treatment (quenching) and one, two, four, and eight ECAP passes were studied. After the first ECAP pass, the alloy strength increases due to the precipitations of the metastable β'' phase on dislocations, while the Guinier-Preston zones are suppressed. This occurs because during the ECAP-induced strain aging process, grain boundary defects are formed, creating quite significant strain conditions that cause the diffusion of alloying elements against the concentration gradient. Silicon and copper atoms are directed into the formed compression zones, and magnesium atoms are directed into tension zones. The process of diffusion against the concentration gradient leads to local decomposition of the supersaturated solid solution, the emergence of new phases and an increased strength. After four ECAP passes, a stable β (Mg₂Si) phase with a size of up to 0.3 μm, a β'' (Mg₅A_l2Si₄) phase, and a secondary CuAl₂ phase are separated. After eight ECAP passes, the release energy of the metastable β' phase decreased from 6.1 J/g to 3.6 J/g, as the supersaturation of the solid solution decreased. The paper presents the temperature ranges for the precipitation of the main phases in 6061  aluminium alloy after quenching and ECAP.