Ultrasonically Assisted Metallizing of Sapphire and Its Brazing to Magnesium Alloys with Zn-Al Alloy

Sapphire is often used as a semiconductor substrate to build complex structural components for connections to magnesium alloys. In this study, a Zn-12Al alloy was treated with ultrasound at 420 °C for 30 s, successfully producing a metallized layer on a sapphire surface. The microstructure and mechanical properties of the joints were investigated. Under the action of ultrasound, epitaxially grown alumina formed on the sapphire surface. The amount of amorphous alumina covering the sapphire surface grew as the ultrasonication time increased, and the sapphire surface was completely covered by ultrasonication for 120 s. Reliable sapphire/Mg joints were obtained by ultrasonic-assisted brazing of metallized sapphire and magnesium alloys at 420 °C. The brazing seam formed an α-Mg solid solution and an α-Mg + MgZn eutectoid structure. The seam gradually filled with eutectoid structure as the duration of the ultrasonication times increased. The joint average shear strength reached a maximum of 27 MPa when the ultrasonication time was 30 s. The fracture primarily occurred inside the α-Mg + MgZn eutectoid structure.