Effects of Sn Interlayer on the Microstructure and Properties of Magnesium–Aluminum Friction‐Stir‐Welded Interface

This study investigated the effects of different Sn interlayers (electroplated Sn and 50 μm Sn foil) on the interfacial reaction, mechanical properties, and corrosion resistance of Mg/Al dissimilar friction stir‐welded joints. The results indicate that the thickness of the Al‐side interfacial intermetallic compound (IMC) layer in the joint without an interlayer reached 8 μm, with continuous strip‐like Al 3 Mg 2 and Mg 17 Al 12 phases distributed at the Mg‐side interface, yielding a tensile strength of 120 MPa. The introduction of Sn interlayers reduced the thickness of the Al‐side IMC layer (3 μm for Sn foil, 2.5 μm for electroplated Sn), whereas Mg‐side IMCs transitioned from strip‐like to dispersed particulate distribution, accompanied by an increase in tensile strength to 130 and 161 MPa, respectively. Electrochemical tests revealed that the joint without an interlayer had the lowest corrosion potential (−1.392 V), with joints with electroplated Sn and Sn foil interlayers exhibiting considerably lower corrosion potentials (−1.271 and −1.272 V, respectively). The electrochemical impedance spectroscopy confirms that SnO passivation films hindered Cl − penetration. The analysis of immersion corrosion morphology indicated that corrosion preferentially occurred at the Mg‐side of the interface. The synergistic effect of Mg 2 Sn phases and SnO passivation films in Sn‐containing joints substantially mitigated galvanic corrosion.