Novel interlayer-free vacuum hot-press bonding of MgAZ31B to brass: microstructural and mechanical insights

Dissimilar Mg/brass joints were fabricated by vacuum hot pressing under a constant pressure of 40 MPa at bonding temperatures of 420–520 °C with holding times of 30–90 min. The interfacial microstructure, diffusion layer evolution, and mechanical properties were systematically investigated. A continuous interfacial reaction layer composed of Mg–Cu-based intermetallic compounds with Zn participation was formed at all bonding conditions. Increasing temperature and holding time promoted diffusion layer thickening due to thermally activated interdiffusion. Mechanical testing revealed a strong dependence of joint strength on interfacial layer thickness. The shear strength increased from 35.4 MPa at 440 °C–30 min to a maximum of 53.5 MPa at 460 °C–30 min, corresponding to the formation of a uniform and moderately thick reaction layer that ensured efficient load transfer. Further temperature increase to 480 °C led to a slight strength reduction (47.7 MPa) attributed to excessive growth of brittle intermetallic compounds. Tensile behaviour showed sequential fracture, with early failure of Mg followed by ductile fracture of brass due to their crystallographic and ductility differences. The results demonstrate that optimising diffusion layer thickness is critical for achieving high-strength Mg/brass diffusion-bonded joints.