A NEW INDUSTRIAL-SCALE METHOD OF THE MANUFACTURING OF THE GRADIENT STRUCTURE MATERIALS AND ITS APPLICATION

摘要

The article describes a novel manufacturing method of materials which exhibit variation in microstructure and thus functional properties along the direction perpendicular to the surface of material. The practical realization of the technological process is based on the combination of surface burnishing with friction heating resulted from the interaction of the tool tip with the material surface. This combination, by creation of specific conditions for plastic deformation, results in the formation of a material with the gradient microstructure which, in turn, contributes to the superior surface layer quality. The obtained results showed that the application of this method, in industrial practice, to porous materials may lead to the formation of the compact, void-free layers with the variable thickness on material surfaces and simultaneously keep geometrical dimensions of the final product with a required accuracy. The presented research pertains to the application of this method to the cast aluminum alloys used for casings of high-voltage switchgear and control gear which are filled with electroinsulating SF_6 gas. The commonly used alloy for this purpose is an aluminum alloy in EN AC-42100 temper (Si 6.5 - 7.5 wt percent , Mg 0.25 - 0.45 wt percent ). The alloy is characterized by good casting and mechanical properties as well as heat treatment ability. However, the products obtained in the casting technology may contain structural discontinuities (porosity, shrinkage porosity). During machining operations, the presence of porosity in a material may be a cause of defectiveness due to high requirements imposed by the leak tightness of flange joints.