Joining of thermoset carbon fiber reinforced polymer and AZ31 magnesium alloy sheet via friction stir interlocking

Friction stir interlocking (FSI), a new derivative friction stir welding, was used to lap join AZ31 magnesium sheet and thermoset carbon fiber reinforced polymer (TS-CFRP) sheet. Instead of directly joining AZ31 and TS-CFRP, a series of magnesium interlocks were used to friction stir weld with AZ31 sheet to enable joining with TS-CFRP. Microstructural characterization of joint cross sections showed that a tool rotation rate of 800 rpm produced incomplete mixing of magnesium interlocks and the top AZ31 sheet, while 1200 rpm achieved sufficient material mixing to avoid unwelded regions. Mechanical property characterization showed that AZ31/TS-CFRP dissimilar joints failed through the magnesium interlock shanks during lap shear tensile testing, with a maximum normalized joint strength reaching similar to 100 MPa. Finite element analysis of the joints helped elucidate the presence of high stress region around the narrow band of the interlock shank providing pathway of fracture.