Ural Federal University, Ekaterinburg, Russia:

Yu. N. Loginov, Professor, e-mail: j.n.loginov@urfu.ru

Revda Non-Ferrous Metals Processing Plant, Revda, Russia:
Yu. A. Sheshukova, Deputy Director on Quality and Ecological Safety
O. A. Khakimova, Head of Laboratory of Physical-Mechanical Testings and Metal Science of the Central Testing Laboratory

The research was conducted on mechanical properties of the complexalloyed CuZn30Al2Mn3SiNiCr brass in a hot-pressed state. This material deals with wear-resistant copper-zinc alloys used for the manufacture of synchronizer rings for vehicle gearboxes. Tests were conducted on samples of a tube billet with an external diameter of 67.8 mm and an internal diameter of 53 mm. The production sequence of these pipes included preparation of an alloy, casting of a continuous casting billet, hot extrusion with scalping and press piercing on a horizontal hydraulic press with a force of 31.5 MN at a temperature of 670 ^оC; a correction on a skew right machine and non-oxidizing annealing in a through furnace at a temperature of 450–470 ^oC and a speed of 3 m/h. A sequence of 720 samples was prepared for measuring Vickers, Rockwell and Brinell hardness at sites with normals in the direction of extrusion, in the radial and tangential direction. The following were measured: hardness in three orthogonal directions, tensile strength values, relative yield strength, elongation and resistivity for samples cut along the direction of extrusion. Statistical processing of the measurement results for the output and sagging parts of the blanks was performed separately. The measurements of mechanical properties of the CuZn30Al2Mn3SiNiCr brass in a hot-pressed state showed that during an industrial production, a significant dispersion of hardness, tensile strength, relative yield strength and elongation before breaking occur, explained by complexity of the chemical composition, phase and structural state of the alloy. The average values in such production conditions were σ_0.2 = 519 MPa, σ_u = 783 MPa, δ = 8%, HRB = 91. The hardness of brass in the sagging part of the pipe was higher than in the case of the outlet part, which can be explained by the phenomenon of metal decay at the end of the deformation process which inhibits the process of recrystallization. A 17% decrease in electrical resistivity of the alloy was observed with the levels of aluminium and manganese decreasing by 0.43% and 0.09%, respectively. The occurrence of hardness anisotropy was determined: when the indenter moves in the radial direction, Vickers, Rockwell and Brinell hardness decrease by 30%, 5% and 9%, respectively, as compared to other directions.
This work was carried out with the partial financial support of the resolution No. 211 of the Government of Russian Federation, contract No. 02.A03.21.0006.

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