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MATERIALS SCIENCE
ArticleName Microstructure and properties of thermally and barothermally processed А319 type casting alloy microalloyed with tin
DOI 10.17580/tsm.2023.06.12
ArticleAuthor Akopyan T. K., Padalko A. G., Letyagin N. V., Pyrov M. S.
ArticleAuthorData

National University of Science and Technology MISiS, Moscow, Russia1 ; Baykov Institute of Metallurgy and Materials Science, Moscow, Russia2:

T. K. Akopyan, Senior Researcher at the Department of Metal Forming1, Research Fellow at Laboratory No. 302, Candidate of Technical Sciences, e-mail: aktorgom@gmail.com

 

National University of Science and Technology MISiS, Moscow, Russia:

N. V. Letyagin, Lead Project Engineer at the Department of Metal Forming, Candidate of Technical Sciences

 

Baykov Institute of Metallurgy and Materials Science, Moscow, Russia:
A. G. Padalko, Head of Laboratory No. 30, Doctor of Chemical Sciences
M. S. Pyrov, Research Engineer at Laboratory No. 30

Abstract

This paper looks at the effect of high external pressure that is applied during barothermal processing of aluminium alloy Al – 7 Si – 3.5 Cu – 0.1 Sn of the А319 type microalloyed with tin. Through differential barothermal analysis conducted at the pressure of 100 MPa, it was found that the phase transition temperatures of the alloy rose from 8 to 11 oC. Through scanning electron microscopy, it was established that, after heat treatment at the temperature of 505 oC and barothermal processing at the pressure of 100 MPa/505 oC/3 h, as the result of thermally activated processes of fragmentation and spheroidization, some microstructural elements – namely, eutectic crystals of the proeutectoid constituents (Si and α(Al(MnFe)Si)) – acquire a more compact morphology, close to the spherical one, with the average particle diameter of 5 to 10 μm. Uniaxial tensile testing of alloy specimens subjected to barothermal processing followed by strengthening T6 heat treatment (for maximum strength), revealed a high level of mechanical properties: ultimate strength – 408 MPa, yield strength — 334 MPa, elongation — 3.1%, compared with the standard level typical of this group of alloys that are not microalloyed with tin. Analysis of the fracture surface in specimens after uniaxial tensile testing revealed standard tiny pits with second-phase particles at the bottom of the pits. The presence of a trace eutectic constituent in the studied concentration range does not lead to brittle intercrystalline fracture. Nor the presence of excessive porosity typical of castings that were not subjected to hot isostatic pressing caused the fracture. By means of scanning electron microscopy, the authors examined the fine structure of the alloy after a full heat treatment cycle, which included HIP followed by T6 heat treatment. It was found that the decomposition products – lamellar precipitates of the metastable θ'-phase, which are ~(50–70) nm long and 3–5 nm thick plates – acquire a disperse structure, with the distribution density being high. Due to the resultant combination of properties, the new group of Al – Si – Cu – Sn alloys can potentially be used for making critical parts, including new generation internal combustion engines.
This research was funded under Governmental Assignment 075-00715-22-00(DBA, DSC, HIP). The structural study was conducted with the help of the equipment of the Shared Knowledge Centre Materials Science and Metallurgy, purchased using the funding provided by the Ministry of Science and Higher Education of the Russian Federation (GK 075-15-2021-696).

keywords Aluminium alloys, silumins, tin microalloying, hot isostatic pressing, differential barothermal analysis, mechanical properties
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