Effect of substrate surface modification with gold on the wetting behavior and reactivity of liquid magnesium in contact with a titanium substrate

Reliable integration of magnesium with titanium is crucial for developing lightweight hybrid structures and advanced biomedical components. However, liquid-assisted manufacturing and coating technologies remain limited by the poor wettability of the Mg/Ti couple at technically relevant temperatures, which arises from the absence of intermetallic compound formation and the immiscibility of the Mg-Ti system. This study investigates the effect of a technological coating designed to enhance wetting, adhesion, and interfacial bonding in the Mg/Ti couple through high-temperature interactions between liquid Mg and a Ti substrate modified with a 40 nm sputtered Au layer. Real-time observation of the high-temperature behavior of the Mg/(Au)/Ti couple was performed using the sessile drop method combined with a capillary purification procedure, which enables the generation of an oxide-free Mg drop directly inside a measuring chamber preheated to 700 °C and filled with flowing Ar + 5 wt% H 2 gas. Immediately upon contact with the substrate, the oxide-free Mg drop exhibited good wettability (θ 0 = 69°) and continued spreading for 540 s of high-temperature interaction, reaching a final contact angle of θ f = 42°. Microstructural characterization of the solidified Mg/(Au)/Ti couple revealed a thin, heterogeneous interfacial region consisting of a continuous MgO layer and localized Mg 3 Au and Ti 3 Au phases. Based on these observations, the interaction mechanism is proposed: (1) solid-state dewetting of the Au coating, exposing local regions of the TiO x surface; (2) dissolution of Au into liquid Mg, forming an interfacial Mg-Au melt; (3) reduction of the TiO x by Mg, producing a continuous MgO layer and oxide-free Ti; (4) reaction of Ti with Au, dissolved in the drop, resulting in Ti 3 Au precipitation at the freshly formed MgO surface; and finally during cooling (5) nucleation of Mg 3 Au from residual Mg-Au melt layer.