Material flow and mechanical properties of aluminum-to-steel self-riveting friction stir lap joints

[Display omitted] [Display omitted] High-quality aluminum /steel joint was achieved via self-riveting friction stir lap welding (SRFSLW) characterized by the prefabricated holes in steel sheet. According to the origination of filling materials, the prefabricated holes were filled with the plasticized aluminum materials in this order: the deformed aluminum ahead of a pin firstly, the stirred aluminum by the pin body secondly and the driven aluminum by the pin tip finally. The strength of the SRFSLW joint reached maximum value of 317 N/mm at the hole diameter of 3 mm, which was 23% higher than that by conventional friction stir welding (FSW). The optimized joints failed at both the aluminum/steel interface and the formed aluminum rivets. The synergistic effect of mechanical bonding induced by the riveting and metallurgical bonding induced by the Al/Fe IMC layer contributed to high strength of the SRFSLW joint.