NOVEL PROCESS OF SURFACE MODIFICATION OF ALUMINIUM CASTS APPLYING FRICTION STIR PHENOMENON

摘要

Aluminum alloys meet a requirement of lightweight vehicles and structural materials, however there are some problems for practical application with less wear resistance. Many attempts were tried to overcome this poor resistance characteristics using fusion processes including welding, laser and plasma processes. However, these fusion processes suffered from defects such as porosity and cracks in the surface modified zone. The friction coating is one of the solid-phase processes with the inherent features including negligible dilution of substrates, no porous defects, a narrower HAZ dimensions as well as the advantage of faster deposition rates. Here, it will deals with the novel process with surface modification using friction. A unique application is called Friction Thermo Mechanical Process (hereafter referred as FTMP) for surface modification of aluminum alloy casts. In this process, a non-consumable rod with small pin is forced to contact with the substrate while rotating. The friction heat, generated at the interface between the rod and the substrate, makes the substrate metal plasticize. The coarse cast microstructures on the substrate surface have been continuously refined due to dynamic recrystallization. As a result, a wider surface modification area can be achieved by FTMP with pin on tool, where the zone within 3 mm depth from the surface can be treated with hardness increment and refined microstructures and cast defects disappear.