The mechanism of the formation of zinc (Zn) pack coatings is studied with scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). DSC showed that the coatings formation takes place in three steps. The initial step (at 193.9°C) is endothermic and involves the transformation of α-NH 4 Cl to β-NH 4 Cl and the NH 4 Cl decomposition to NH 3 and HCl. During the second step (at 248.6°C), which is exothermic, Zn 2+ salts are formed and especially ZnCl 2 . Finally at 264.1°C Zn is deposited by an endothermic reaction on the ferrous substrate through the decomposition of ZnCl 2 . The as-cast Zn diffuses into the iron lattice forming the gamma (Γ-Fe 11 Zn 40 ) and delta (δ-FeZn 10 ) phases. Al 2 O 3 is not involved in the above-mentioned mechanism and acts only as filler.