Improvement of impact strength for friction welded joint by adapting the shape of weld interface

The friction welding for copper and aluminium is useful to minimize the diffusion thickness at the interface between copper and aluminium. However, it is generally difficult to maintain the joint strength. Because brittle intermetallic compounds are necessarily formed at the friction weld interface between copper and aluminium. In this study, stress singularities at free-edge and intersection of copper/aluminium interface were investigated using finite element analysis. It was informed that the no free-edge stress singularities existed below an apex angle of 59° and between angles of 98° and 129°. Also, intersection stress singularities exist over all apex angles except an apex angle of 90°. However, in case of apex angles between 98° and 129°, compressive stress concentration existed near the intersection of copper/aluminium interface. In this experiment, copper and aluminium friction welded joints were fabricated as to minimize (> 1 μm) the welding condition of the diffusion thickness at the interface between copper and aluminium. It was confirmed that the good tensile strength could be observed in all specimens tested. However, the Charpy impact energy became comparatively low in case of an apex angle of 90° and 135°, and showed a remarkable high impact energy can be obtained in case of no free-edge stress singularities.