STRUCTURE FORMATION IN SURFACE LAYERS OF ALUMINUM AND TITANIUM ALLOYS DURING PLASMA CUTTING

Abstract

This paper explores the structure and changes in the mechanical properties, chemical composition and surface morphology of aluminum alloys AA5056, AA2024 and Grade2 titanium alloy after high energy impact during plasma cutting. The studies show that plasma cutting causes the formation of a subsurface layer with a dendritic structure typical of cast material and with a partially altered chemical composition. The subsurface layer material is significantly softened when cutting thermally hardened alloy AA2024, but changes slightly when cutting AA5056 alloy. During plasma cutting of Grade2 titanium alloy in protective atmosphere, the presence of even a small amount of atmospheric oxygen leads to the formation of oxides in the layer closest to the surface, which have microhardness values more than 5-7 times higher than the base metal hardness. Below the surface layer with a molten structure, a heat affected zone is formed where the structure of the base metal is changed as a result of thermal influence. Significant changes in this area are characteristic only for thermally hardened alloy AA2024. Metal flow in the cutting zone initiated by the plasma jet and shielding gas flow occurs in both laminar and vortex modes. Inhomogeneous metal flow in the cutting zone and nonoptimal process parameters lead to the formation of structural heterogeneities and defects of different structural and scale levels on the surface of the samples.