Friction Stir Incremental Forming of AA7075-O Sheets: Experimental Investigations on Performance Evaluation of Formed Parts

A comprehensive performance of formed parts by AA7075-O sheets was studied in friction stir incremental forming (FSIF). Various tool rotation speeds were set to form two typical parts (truncated funnel and pyramid frustum). The formability, surface quality, tensile strength, micro-hardness and thickness distribution of the formed parts were investigated. Results show that the formability generally increases as tool rotation speeds increase. On the contact surface, variation trends of the surface roughness are different in horizontal direction (parallel to tool path) and vertical direction (perpendicular to tool path). However, the surface roughness on the non-contact surface is almost not affected by tool rotation speed. Furthermore, mechanical properties including tensile strength and surface micro-hardness in formed parts are obviously enhanced compared to those of the initial sheet, of which the hardness values begin to fall down gradually after rotation speed reaches 3000 r/min. As for thickness measurement, more uniform thickness distribution of formed parts can be obtained at relative high tool rotation speeds. In general, parts formed at high rotation speed have a better comprehensive performance except the mechanical property.