Characterization of an Active Soldering Zn-Mg Alloy and the Study of Ultrasonic Soldering of SiC Ceramics with Copper Substrate

The aim of this study was to characterize a Zn-Mg type soldering alloy and direct soldering of SiC ceramics with a copper substrate. The Zn1.5Mg solder exerts a wider melting interval. The temperature of the eutectic reaction was 365 degrees C, and the liquidus temperature was 405 degrees C. The microstructure of the soldering alloy is comprised of a zinc matrix. Segregation of binary eutectics in the form of (Zn) + Mg2Zn11 lamellas occurred on the boundaries of Zn grains. Additionally, the presence of a MgZn2 magnesium phase was observed in the solder matrix. The SiC/solder bond was formed due to magnesium distribution from solder to the boundary with SiC ceramics, where magnesium reacts with silicon, which is infiltered in SiC ceramics. By a mutual interaction, a new Mg2Si phase is formed. An interaction between the molten zinc solder and Cu substrate occurred on the boundary of the Cu/substrate joint at the formation of a transition zone composed of two new phases, namely the gamma Cu (Cu5Zn8) non-wettable phase type, approximately 30 mu m wide, and a wettable (CuZn4) phase type epsilon, approximately 12 mu m wide. The average shear strength of a combined SiC/Cu joint fabricated using Zn1.5Mg solder was 44 MPa.