Microstructural investigation of donor material experiments in friction stir welding

摘要

Excessive tool wear generated during the plunge phase of Friction Stir Welding is hindering the application of Friction Stir Welding to hard materials such as steel. In this research we introduce a donor material concept by which we develop localized pre-heating that minimizes the forces throughout the tool which results in reducing tool fracturing and subsequent production replacement. Initial donor material experiments of Cu/Al were conducted to confirm the feasibility of applying this method to the FSW process. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) images of the donor material depict no mixing of Cu with Al at the interface of the Al plate during plunge. The microstructural images indicate formation of columnar grains and grains recrystallization at the interface. The EDX images that represent several locations from shallow at the surface of the Cu plate to deep positions inside the plunge zone of the Al plate indicate the progression of the Cu/Al composite. A finite element model of the Johnson-Cook material constitutive law is used to investigate the shear stresses, axial forces, and temperature developed during the plunge stage in donor material and steel.