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

E. A. Naumova, Associate Professor at the Department of Metal Forming, e-mail: jan73@mail.ru

E. S. Vasilieva, Master’s Student at the Department of Metal Forming

Moscow Polytechnic University, Moscow, Russia:
М. А. Petrov, Associate Professor at the Department of Metal Forming and Additive Technologies
B. A. Stepanov, Professor at the Department of Metal Forming and Additive Technologies

Specimens of the Al — 15% Ca alloy comprising more than 55% of the Al₄Ca intermetallic compound were subjected to hot and cold stamping with torsion. Alloys with a high concentration of intermetallic compounds can be used as materials with a low thermal expansion ratio. Stamping with torsion creates severe shear strains. The material structure sees quality changes in the tangential direction, and a fine-grained structure is formed, which enhances the mechanical and physical properties of the material. The equipment used in this research is capable of producing large workpieces with diameters reaching 150 mm. An electric resistance furnace was used to produce the experimental alloy. For better ductility, the cast specimens were annealed at 550 ^оС in a laboratory furnace. Such annealing procedure results in fragmented eutectic intermetallic compounds which then become of a round shape. For hot stamping with torsion, the stamp was heated to 450 ^оС, while the temperature of the workpiece was raised to 500 ^оС; pressure applied – 1 MN; die rotation – 180 degrees. No heat was applied to either the stamp or the workpiece during cold stamping, the same pressure and die rotation were applied as during hot stamping. The microstructure of the primary cast specimens contains aluminium-calcium eutectics, as well as primary crystals of the Al₄Ca intermetallic compound of a round or platelet shape. Multiple pores are also present in them. The microstructure of the specimens after hot and cold stamping with torsion is quite non-homogenous. Compared with the peripheral areas, the centre of the specimens has a more consistent structure, finer intermetallic particles, and a higher hardness. The resultant specimens have almost no pores, the primary intermetallic compounds are fragmented and evenly distributed in the specimens, and the hardness rises almost twice compared with the as-cast state.
This research was funded by the grant 14-19-00632P (metallographic study) of the Russian Science Foundation and under the Assignment No. 11.2072.2017/4.6 (experimental stamping with torsion).

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