INFLUENCE OF GRAIN-BOUNDARY OPENINGS ON F RACTURE MECHANISMS IN WELDED ALMGSI ALLOYS

In the present investigation AlMgSi0.7 extruded samples were welded wi th AlMg5 filler metal under conditions which favoured the formation of Grain Boundary Openings (GBO) in the heat affected zone. Fractographi c examinations showed that GBO influence the fracture mechanisms. Appl ying specific fatigue block loadings the crack growth could be made vi sible on the fracture surface. It was demonstrated that a GBO does not behave like a sharp crack in the sense of classical fracture mechanic s with immediate growth on application of stress. After a certain time of fatigue a crack is created at a GBO depending mainly on the stress amplitude. It is shown that a weld defect tolerated by standards can cause a more effective risk for fracture than the presence of the abov e mentioned GBO.