Formation of Al–Mo intermetallic particle-strengthened aluminum alloys by friction stir processing

This study investigated the formation of Al–Mo intermetallic particle-strengthened aluminum alloys from the mixture of Al and Mo powders by using friction stir processing (FSP). The FSP resulted in considerable plastic deformation and heat input from the rotating pin and its shoulder against the sample. In this process, the hot working nature of FSP can effectively promote the exothermic reaction between Al and Mo to produce fine Al–Mo intermetallic particles with an average size of approximately 200 nm. The Al–Mo intermetallic particles formed during FSP were identified mainly as Al12Mo with a small amount of Al5Mo. The Al–Mo reaction during heat treatment without the help of concurrent shear deformation was relatively slow because it was controlled by the interdiffusion through the Al12Mo phase. The critical mechanism responsible for the rapid reaction and the formation of nanometer particles in FSP was the effective removal of the Al12Mo phase from the Al–Mo interface, which was caused by the shear force imposed by the rotating tool pin.