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

P. K. Shurkin, Post-Graduate Student, e-mail: pa.shurkin@yandex.ru
N. O. Korotkova, Post-Graduate Student of a Chair of Foundry Technologies and Material Art

Baikov Institute of Metallurgy and Material Science, Russian Academy of Sciences, Moscow, Russia:

T. K. Akopyan, Researcher

This paper describes the possibility of increasing the mechanical properties by hot isostatic pressing (HIP) operation of the castings made of high strength sparingly alloyed aluminum alloy (based on the Al – Zn – Mg – Cu – Ni – Fe system), which was produced using a low-grade zinc with high content of lead and iron impurities. We obtained the chill castings, which were subsequently subjected to hardening heat treatment (quenching followed by an artificial aging to the maximum strength). Part of the party of castings was preliminary subjected by the HIP treatment, and then also heat treated to the maximum strength. The microstructural studies using a scanning electron microscope shown that the structure of castings, which are not subjected to HIP, contains a large amount of fine lead inclusions. After barothermal treatment the microstructure takes the typical form for high strength nikalins with iron content, and lead inclusions are found significantly less. The density of castings after the HIP increases and becomes close to the theoretical value since the porosity is eliminated almost completely. According to the results of tensile test, the castings, which were not subjected to the HIP, are very brittle, and most of them are destroyed without elongation. The improvement of structure after the HIP provides the increase of properties. So the strength of castings increased by more than 60 MPa and the ductility increased 10 times more. It is also important to note the significant reduction of the mechanical properties values scatter. In particular, the scatter decreases more than two times for elongation and more than 90% for tensile strength. The fracture surface after the tensile test of the samples, which were subjected to the HIP treatment, contains numerous dimples and has a ductile character of fracture. In contrast, the fracture surface of the samples, which were not subjected to the HIP treatment, is characterized by an arrangement of the lead inclusions at the grain boundaries, which is the reason of the brittle intergranular fracture.
This paper was written within the Subsidiary Agreement No. 14.578.21.0039 (unique identifier of the project RFMEFI57814X0039; the Ministry of Education and Science of Russian Federation) within the realization of the Federal Target Program “Investigations and developments of the priority ways of development of scientific-technological complex of Russia for 2014–2020”.

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