The effect of the heat generated during friction stir welding process on different aluminum alloys

Aim of this paper is the study of the effect of the heat generated, in both temporal and spatial terms, during the friction stir welding process on precipitation-hardening and work-hardening alloys. In order to analyze the thermal distribution within the joints, the temperatures reached during the traditional air-cooled process and with an external water-cooling system were measured at the nugget, the thermo-mechanically affected zone and the heat affected zone. After performing tensile and Rockwell tests, a clear dependence of the thermal gradient on all the mechanical properties of the joints was observed. In particular, it was noticed that the change in the water-cooled joints properties of the precipitation-hardening alloys depends on both the distribution of the hardening precipitates and the grains size. Moreover, a virtual model was set up to predict the temperatures reached locally by the joint and consequently the overall mechanical properties.