Friction stir processing: Thermo-mechanical loads and consequent effects on the local material characteristics

The present article is focused on the correlation between the applied thermal and mechanical loads and the consequent effects on the material in friction stir processing (FSP) operations. On one hand, the actions exerted in FSP are split compared to the results obtained with a tool without the pin at its end to a traditional one with a cylindrical pin. In this way, the thermal flux determined by the frictional forces at the tool—shoulder—workpiece interface is secluded from the mechanical stirring action made by the tool pin. On the other hand, the processed specimens are analysed in terms of residual stress state, microhardness, and average grain size values. An in-process heat treatment of the processed blanks was also carried out to highlight the single local actions and effects on the material. The obtained results permit to determine cause—effect correlations between the considered inputs and outputs. AA7075-T6 aluminium blanks were used for the study.