Siberian State Industrial University, Novokuznetsk, Russia

S. V. Konovalov, Vice Rector for Research and Innovation, Chief Researcher at the Industry-Specific Research Laboratory No. 42, Doctor of Technical Sciences, Professor, e-mail: konovalov@sibsiu.ru

Siberian State Industrial University, Novokuznetsk, Russia¹ ; Samara National Research University, Samara, Russia²
E. V. Aryshenskii, Senior Researcher at the Research Laboratory of Electron Microscopy and Image Processing¹, Leading Researcher at the Industry-Specific Research Laboratory No. 4², Doctor of Technical Sciences, Associate
Professor, e-mail: ar-evgenii@yandex.ru

SMP JSC, Samara, Russia

M. A. Lapshov, Lead Design Engineer, e-mail: Maksim.Lapshov@samara-metallurrg.ru

Samara National Research University, Samara, Russia
A. M. Drits, Lead Researcher at the Industry-Specific Research Laboratory No. 4, Candidate of Technical Sciences, e-mail: dritsam@gmail.com

This paper looked at the (AlSi)3ScZr particles that precipitate in Al – Mg – Si alloys with excessive silicon when they are cooling down after casting. The effect of nanoparticles on strength is demonstrated in as-cast state. The effect of artificial ageing on the mechanical properties of studied alloys is also demonstrated. The paper examines six Al – Mg – Si alloys with different Mg/Si ratios and with scandium and zirconium additives or without them. Microhardness and mechanical properties were determined for all alloys in as-cast state. To look at the decomposition of supersaturated solid solution, specimens of alloys containing scandium and zirconium were annealed in the temperature range of 360 to 550 ^oC, with the soaking time varying between 10 and 50 hours. Using optical microscopy, the grain structure was studied for alloys with Mg/Si = 0.6. Besides, a scanning microscopy study of nanoparticles was conducted for 0.6MgSi0.3Sc0.15Zr alloy. For 0.3MgSi0.3Sc0.15Zr and 0.5MgSi0.3Sc0.15Zr alloys, the data about the grain structure and nanoparticles were taken from previous research studies. The results show that the solid solution supersaturated with scandium, zirconium, silicon and magnesium in the studied alloys has an extremely short decomposition time. It happens because of the combined effect of scandium and silicon. Because of the fast decomposition of the supersaturated solid solution, a great number of (AlSi)3ZrSc particles is formed when it is cooling down after casting. The main mechanism behind it is an intermittent decomposition of the supersaturated solid solution suggested by the presence of fan-shaped particles. Particles detected in the 0.6MgSi0.3Sc0.15Zr alloy retain the L12 structure, are partially coherent with aluminium matrix and contain silicon and scandium. Considering their morphology, sizes and chemical composition, they cannot belong to Sc2Si2Al phase. At the same time, they do impact the mechanical properties. Thus, in the 0.6MgSi0.3Sc0.15Zr alloy the yield strength rises by 43 MPa and the ultimate strength – by 61 MPa. The 0.3MgSi0.3Sc0.15Zr and 0.5MgSi0.3Sc0.15Zr alloys also gain higher strength, which is due to the fan-shaped semi-coherent and round fully coherent (AlSi)3ScZr particles detected in previous research studies in as-cast state. It was found that in the 0.3MgSi0.3Sc0.15Zr and 0.5MgSi0.3Sc0.15Zr alloys the yield strength rises by 32 and 67 MPa and the ultimate strength – by 67 and 78 MPa, respectively. During artificial ageing, microhardness can either rise or drop. The grain structure size produces the strongest effect on microhardness during artificial ageing: the larger the grain size is, the higher the microhardness is after artificial ageing of as-cast material.

Support for this research was provided under Grant No. 21-19-00548 https://rscf.ru/project/21-19-00548/ by the Russian Science Foundation.

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