Friction stir incremental forming of AA7075-O sheets: investigation on process feasibility

Abstract

Abstract Friction Stir Incremental Forming (FSIF), as a simple and effective hot incremental forming technology, has attracted increasing attentions from researchers in recent years. In FSIF, frictional heat generated by tool rotation on the interface between tool and workpiece is utilized to soften localized deformation zone, thus enhancing material formability. In order to facilitate the development of FSIF, a comprehensive analysis of process feasibility is needed for the performance evaluation of formed parts. In this work, FSIF has been employed to process 7075-O aluminum alloy sheets (a kind of hard-to-form light alloy materials) for assessing the formability, surface quality, tensile strength and micro-hardness of two typical parts (truncated funnel and pyramid frustum). Experimental results show that the formability generally enhances with the help of local frictional heating as tool rotation speeds increase. On the tool-sheet contact surface, surface roughness shows a different trend of variation in horizontal (parallel to tool path) and vertical directions (perpendicular to tool path). Furthermore, mechanical properties including tensile strength and surface micro-hardness in formed parts are obviously enhanced compared to the initial sheet, of which the micro-hardness values begin to fall down gradually when the tool rotation speed is greater than 3000 rpm.