Investigation of modified friction stir clinching-brazing process of AA2024 Al/AZ31 Mg: metallurgical and mechanical properties

The weldability of the AA2024-T3 and AZ31 Mg alloys was investigated using the modified friction stir clinching-brazing (MFSC-B) and probe-less friction stir spot brazing (PFSSB) processes. A 50 µm thick Zn foil-interlayer was sandwiched between the dissimilar base materials for the welding processes. The mechanical, microstructure, and weld-fracture behaviors of all joints were studied and compared. Zn-rich interdiffusion-aided lamellar and blocky structures are found at the brazed region/zone of the AA2024-T3/Zn/AZ31 joint irrespective of the welding process due to the sole influence of heat input at the zone. The differential flow in the MFSC-B joint enforces significant inter-material mingling, better distribution of Zn, and more subgrains/dislocation density at the joint as compared to the PFSSB joint. The interlayer inhibited the creation of the β-Al₃Mg₂ phase while the γ-Al₁₂Mg₁₇ phase could not be prevented in the AA2024-T3/Zn/AZ31 joints due to tool-induced atomic collision and diffusion–reaction mechanisms. Improved tensile/shear failure load is found in the MFSC-B joint (4369 N) as related to their PFSSB counterpart (3018 N) due to improved material flow (intermixing), and intense dislocation density. The MFSC-B process is thus recommended for dissimilar joining of Mg and Al alloys.