Friction stir welding of dissimilar 7075 aluminum/AISI 304 stainless steel joints was done using different tool rotational speed values. The weld was mainly formed in the aluminum part due to the offset value, and stainless steel particles were surrounded with the stirred fine-grained Al matrix. Intermetallic compounds consisting of FeAl3, Fe3Si, FeAl, Fe4Al13 and Fe3Al2Si4 were found in the weld bead. The thickness of the intermetallic compound layers was increased up to 6 μm by increasing the tool rotational speed. Moreover, the stir zone was mainly characterized by a composite-like structure. The weld strength was increased significantly by decreasing the tool’s rotational speed. The maximum strength of joints was about 72% of 7075 aluminum strength. The formation of extensive intermetallic compound layers could be the reason for the reduced joint strength. In specimens with higher tool rotational speeds, fracture occurred within the stir zone.

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