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Abstract

In this article the structural and mechanical properties of grain refinement of Cu-Sn alloys with tin content of 10%, 15% and 20% using the KOBO method have been presented. The direct extrusion by KOBO (name from the combination of the first two letters of the names of its inventors – A. Korbel and W. Bochniak) method employs, during the course of the whole process, a phenomenon of permanent change of strain travel, realized by a periodical, two-sided, plastic metal torsion. Moreover the aim of this work was to study corrosion resistance. The microstructure investigations were performed using an optical microscope Olimpus GX71, a scanning electron microscope (SEM) and a scanning transmission electron microscope (STEM). The mechanical properties were determined with INSTRON 4505/5500 machine. Corrosion tests were performed using «Autolab» set – potentiostat/galvanostat from EcoChemie B.V. with GPES software ver. 4.9. The obtained results showed possibility of KOBO deformation of Cu-Sn casting alloys. KOBO processing contributed to the refinement of grains and improved mechanical properties of the alloys. The addition of tin significantly improved the hardness. Meanwhile, with the increase of tin content the tensile strength and yield strength of alloys decrease gradually. Ductility is controlled by eutectoid composition and especially δ phase, because they initiate nucleation of void at the particle/matrix interface. No significant differences in the corrosion resistance between cast and KOBO processed materials were found.
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Abstract

The article presents tests results of metalforming of magnesium alloy AZ61. Materials for tests were ingots sized  40×90 mm from magnesium alloy marked with symbol AZ61. Before the shaping process the ingots underwent heat treatment. As a result of conduction of the deformation processes there were rods achieved with diameter of 8 mm. There were axisymmetrical compression tests conducted on the samples taken from rods in temperature range from RT to 350ºC in order to determine the plasticity and formability of the alloy AZ61. Static tensile test was conducted in room temperature (RT), in 300ºC and in 350ºC. With the use of light and electron microscopy techniques the changes which occurred in the microstructure of AZ61alloy in initial condition and after plastic deformation (classic extrusion, KoBo method extrusion) were described. The deformation of alloy AZ61 using the KoBo method contributes to an increase in strength and plastic properties. The effect of superplastic flow was found at a temperature of 350ºC, where a 300% increase in plastic properties – elongation value was obtained. The analysis of the microstructure showed a significant grain size reduction in the microstructure of alloy AZ61 after deformation by the KoBo method and after an axisymmetric compression test, where grains of an average diameter of d = 13 µm were obtained.
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