Abstract
Wear resistance of duplex hard-coated die for aluminum extrusion are investigated. Nitrided layer of duplex hard-coat was prepared by gas nitriding, plasma ionic nitriding or plasma radical nitriding method, and the 3 μm hard coat films, CrN, TiN or TiAlN was by arc ion plating on the nitrided layer. Hardness, friction coefficient, critical load and roughness of duplex hard-coated specimens (SKD61) were observed before and after oxidation at 500°C or 650°C, atmosphere, 5h. Hardness of coated area of die before extrusion and after removal of adhesive aluminum were compared. Hardness of duplex hard-coat and single hard-coat were also compared. In the case of single hard-coated die which critical load was under 30 N, hard-coat in the front bearing area was deteriorated. On the contrary, duplex hard-coat which critical load was over 60 N, was hardly changed after 5 extrusions. Duplex hard-coated dice showed higher wear and oxidation resistance in comparison with dice singly hard-coated because the hardness of nitrided layer was nearly unchanged after heating at atmosphere.
