Friction welding of tungsten heavy alloy with aluminium alloy

This paper is a study of mechanical properties and microstructure of friction welded coupe of weight heavy alloy (WHA) with aluminium alloy (AA). Scanning electron microscopy (SEM) was used for investigation of the fracture morphology and phase transformations taking place during friction welding process. Chemical compositions of the interfaces of the welded joints were determined by using energy dispersive spectroscopy (EDS). Effects of friction time (FT) and friction pressure (FP) on the ultimate tensile strength (UTS) were studied by plotting graphs. The maximum average strength of 234 MPa, which is 84.78% of the aluminium alloy base material, is achieved at a friction time of 3.5 s and friction pressure of 40 MPa, respectively. The UTS of joints increases with increasing of FP and FT and then decreases after reaching the maximum value, with increase of friction load and time. Microstructure of friction welds consisted of fine equiaxed grains (formed due to dynamic recrystallization) and coarse grains in the periphery region on AA side. A plastic deformation in the direction of burrs is visible mainly on AA side. EDS-SEM scan line analyses across the interface have not confirmed the diffusion of tungsten and nickel to AA side. The nature of the friction welding joints is rather adhesive than diffusive. The EDS point spectrometry showed some enrichment of Ni-Fe matrix with Al atoms close to the joint. Absence of intermetallic phases was found in the weld interface on SEM level observation. The fracture procedes mainly through the cleavage planes at the interface.