Improving the Interfacial Microstructure and Properties of Al/Mg Bimetal by a Novel Mo Coating Combined with Ultrasonic Field

To enhance the interfacial performance of Al/Mg bimetal, this study introduced a novel Mo coating and employed an ultrasonic field (UF) to regulate the interfacial microstructure. In the absence of both a Mo coating and ultrasonic treatment (referred to as the untreated specimen), the interfacial region was primarily composed of Al-Mg intermetallic compounds (Al-Mg IMCs), Al-Mg eutectic structures (ES), and Mg₂Si phases, with an average interfacial layer thickness of approximately 1623 μm. Upon application of the Mo coating, the formation of both Al-Mg phases and Mg₂Si phases was completely inhibited. The interfacial zone was predominantly characterized by the Mo solid solution (Mo SS) and oxide, with the average thickness significantly reduced to about 28 μm. Upon applying the UF to the Mo-coated specimen, the interfacial composition remained similar to that of the untreated specimen, except for Mo SS, with the interfacial thickness increasing to 561 μm. Shear strength tests indicated that the application of the Mo coating alone resulted in a decrease in bonding strength compared to the untreated specimen. However, subsequent ultrasonic treatment significantly improved the interfacial shear strength to 54.7 MPa, representing a 60.9% increase relative to the untreated specimen. This improvement is primarily attributed to the Mo coating and UF synergistically suppressing the formation of brittle Al-Mg IMCs and reducing oxide inclusions at the interface. Thus, the simultaneous application of Mo coatings and ultrasonic fields is required to enhance the properties of Al/Mg bimetals.