All-Russian Scientific Research Institute of Aviation Materials, Moscow, Russia:

S. V. Sbitneva, Senior Researcher, e-mail: admin@viam.ru
A. A. Alekseev, Chief Researcher
P. L. Zhuravleva, Leading Engineer
N. I. Kolobnev, Chief Researcher

This paper investigates the phase transformations during aging in 6013 and 1370 alloys (Al – Mg – Si – Cu system), containing 0.8–1.0% (wt.) of Cu. Transmission electron microscopy verified the crystal structure of non-equilibrium phases, aging according to the Q-type (Al₅Cu₂Mg₈Si₆). Lattices of these phases have different parameters and orientation relations with matrix. The Q-phase structure was defined on the particles formed as a result of overaging (230 ^оC, 32 h). Morphology and habitus of the β’- and Q’-phase particles were defined. Morphology of β’-phase (Mg₂Si) particles is rod-shaped, while morphology of non-equilibrium Q’-phase particles is lath- and rod-shaped. The laths have two types of habitus: {510}_Al and {320}_Al. Diagrams of phase transformations during aging were constructed according to the research results, marking the time temperature areas of Q-type phases existence. Formation of Q-type phase corresponds to higher temperatures and duration, than formation of β’’ and β’-phase. Decomposition mechanism of the supersaturated solid solution (SSS) in this system alloys is offered. Formation of Mg₂Si cluster requires shorter diffusion displacements than formation of composition fluctuations, containing Al, Mg, Si and Cu in right proportions. Therefore, Cu atoms are released from SSS in the last turn. There was analyzed the correlation between the SSS decomposition products near the grain boundary region during the step aging and resistance to intercrystalline corrosion (ICC) in 1370 alloy. There were developed the step modes of aging, which provide high strength properties and good resistance to ICC (ICC depth is less than 100 microns).
This work was carried out with the financial support of the Ministry of Education and Science of the Russian Federation within the agreement about the subsidy No. 14.595.21.0002 (22.08.2014), unique identifier No. RFMEFI59514X0002, using the equipment of the “Climatic Testings” Center (All-Russian Scientific Research Institute of Aviation Materials).

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