The thickness of sheet metal parts can be locally increased by friction drilling technology via forming of a hole with a bush by a special drilling tool. Here, a 7075 Al-alloy was drilled by friction using tool cone angles with values of 40, 45 and 50⁰ under different feed rates (100, 200 and 315 mm/min) and rotational speeds (1000, 1250 and 1600 rpm). The present study investigates the hardness distribution in the thermally-formed bush and in the heat-affected zone around the bush. It was found that the hardness of the bush was slightly increased with increasing of the tool cone angle and reduction of the tool rotational speed. However, the hardness of the thermally-induced bush showed values lower than the parent metal. The hardness near the drilling surface was approximately 65±10 HV, while it recorded hardness values of 75±10 HV at 5 mm away from the drilling surface. In addition, the microstructure of the friction drilled specimens showed a very fine structure in the drilling zone due to crushing of the original structure during the friction drilling process. |
