<p>This study focused on the high-temperature behavior of pure liquid Mg on three dissimilar types of cast iron substrates (Fe-C alloys with different morphologies, quantities, and distributions of the graphite phase). The experiments were performed using the sessile drop method under isothermal conditions at 715&#xa0;°C in two different flowing gas atmospheres: (i) pure Ar and (ii) a mixture of Ar and 5 wt% H₂. The tests were conducted using non-contact heating of a couple of dissimilar materials combined with capillary purification of Mg drops from a native oxide film directly at the test temperature in an experimental chamber by squeezing the drops from a graphite capillary placed above cast iron substrates. The high-temperature behavior of Mg/substrate couples was recorded with a high-speed CCD camera, and collected images were used for measurements of the contact angle values (θ) formed between the liquid Mg and selected substrates. The solidified Mg/substrate couples were subjected to detailed microstructural observations by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). The obtained results showed significant differences in the wetting behavior of Mg depending on the type of cast iron and the test atmosphere. In all cases, non-wetting behavior (θ &gt; 90°) was observed in pure Ar, while the addition of hydrogen led to a reduction in contact angle values, especially for spheroidal graphite iron (SGI), where values decreased below 90°, commonly accepted as wetting behavior. In contrast, lamellar graphite iron (LGI) remained non-wettable under both atmospheres used in this study, although a decrease in contact angle (Δθ ~ 27°) was determined in the hydrogen-containing atmosphere, as compared to pure Ar. Compact graphite iron (CGI) also exhibited non-wetting behavior in both atmospheres; however, the values of contact angle were close to 90° in the Ar + 5 wt% H₂ atmosphere. The SEM/EDS analysis of cross-sectioned solidified Mg/cast iron substrates revealed slight morphological differences. For SGI and CGI, localized interface areas containing Mg, O, and occasionally Si were observed, particularly after testing in the Ar + 5 wt% H₂ atmosphere. These areas were generally thin and discontinuous, and no evidence of new phases was found. The presence of isolated Mg crystallites on the LGI surface was attributed to mechanical deposition or condensation of Mg during cooling.</p>