Reactive wetting of amorphous silica by molten Al–Mg alloys and their interfacial structures

Highlights: • The wettability improves with increasing Mg concentration and temperature. • Reaction product zone consists of layered structures relating with Mg concentration. • Formation of MgAl₂O₄ and MgO at the interface does not promote the wettability. • Formation of Mg₂Si plays a dominant role in promoting the wettability. • Anomalous recession of the triple line was mainly due to diminishing Mg in the alloy. - Abstract: The reactive wetting of amorphous silica substrates by molten Al–Mg alloys over a wide composition range was studied using a dispensed sessile drop method in a flowing Ar atmosphere. The effects of the nominal Mg concentration and temperature on the wetting and interfacial microstructures were discussed. The initial contact angle for pure Al on the SiO₂ surface was 115° while that for pure Mg was 35° at 1073 K. For the Al–Mg alloy drop, it decreased with increasing nominal Mg concentration. The reaction zone was characterized by layered structures, whose formation was primarily controlled by the variation in the alloy concentration due to the evaporation of Mg and the interfacial reaction from the viewpoint of thermodynamics as well as by the penetration or diffusion of Mg, Al and Si from the viewpoint of kinetics. In addition, the effects of the reaction and the evaporation of Mg on the movement of the triple line were examined. The spreading of the Al–Mg alloy on the SiO₂ surface was mainly attributed to the formation of Mg₂Si at the interface and the recession of the triple line to the diminishing Mg concentration in the alloy.