High-temperature interactions of liquid magnesium with a pure copper substrate

Abstract

For the first time, experimental results of the high-temperature interaction of liquid magnesium with pure copper are presented. The investigation was performed using the sessile drop method and capillary purification procedure allowing both non-contact heating of the Mg/Cu couple and in situ cleaning of the Mg drop from a native oxide film. The test was done under isothermal conditions at 710 °C in a protective atmosphere, which was a mixture of Ar + 5 wt% H2.The images of the Mg/Cu couple collected during the high-temperature measurements were used to determine the time-dependent values of the contact angle (θ) formed between the liquid magnesium drop and the copper substrate.The solidified couple was subjected to detailed microstructural observations by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), both coupled with energy-dispersive X-ray spectroscopy (EDS).Under the applied measurement conditions, immediately after contact with the Cu substrate, the liquid Mg drop showed a very good wetting (θ0 ∼ 22°), followed by rapid spreading over the substrate, forming a final contact angle θf ∼ 11°. However, SEM/EDS analysis revealed that θf is an apparent angle due to the deep crater (∼200 μm) formed in the substrate under the Mg drop by the dissolution of Cu in liquid Mg.The comparative SEM/TEM/EDS analysis suggests that good wetting and rapid spreading in the Mg/Cu couple are dominated by the reactive wetting mechanism due to the dissolution of the Cu substrate in the liquid Mg drop and its saturation with a high amount of dissolved Cu. Consequently, the microstructure of the solidified drop was composed of large Cu-rich primary MgCu2 crystals surrounded with a two-phase eutectic mixture (MgCu2 + Mg2Cu) formed at the final stage of cooling. In addition, the MgCu2 phase was also nucleated and grown at the Mg/Cu interface to form a continuous layer.