Adhesion Mechanism of Galvannealed Steel Sheet during Flat Sliding Test Studied by Microscopic Analysis of Die Surfaces

Abstract

The surfaces of dies used for flat sliding tests of galvannealed steel sheet (GA) have been investigated using several electron microscopic techniques in order to clarify the adhesion mechanism. Two kinds of adhesive materials were identified on the die surface. One consists of an Al oxide – Fe–Zn alloy composite and tightly bonds to ridges of the die surface. This resembles the built-up edges formed on tool surfaces during metal-cutting operations. Another adhesive material is composed of Fe–Zn alloys located in the hollows of the die surface which do not bond or only loosely bond to the die surface. A new adhesion model consisting three steps is proposed; (1) the Al oxide – Fe–Zn alloy composite layers are formed on the ridges of the die surface. (2) The Fe–Zn intermetallics on the GA surfaces are cut by this layer and (3) accumulate in the hollow of the die surface.