Effects of the process parameters on the formation of the Zn-enriched surface layer of Mg by thermochemical treatment in a medium containing ZnCl2

The fabrication of the Zn-enriched surface layer of Mg involved annealing of the Mg specimens in a contact with the paste containing ZnCl2. Annealing of the specimen at 440 ⁰C
for 120 min resulted in the formation of a surface layer with a complex structure. In the outer zone, dendrites of a solid solution of Zn in Mg were observed at a eutectoid matrix (an MgZn intermetallic phase and a solution of Zn in Mg). The inner, transition zone, which was located at the interface adjacent to Mg substrate, was composed of a solid solution of Zn in Mg. The use of various period of annealing time (30, 60, 90 and 120 min) showed that increasing the annealing time leads to an increase in the thickness of the layer. A similar structure of the layer was observed for each variant of the annealing time. The analysis for the specimen fabricated at 410 ⁰C for 120 min showed that the use of lower temperature resulted in a formation of a thin layer, eutectoid in structure. When higher annealing temperature (470 ⁰C) was used, the thick surface layer with an uneven thickness and containing macroscopic unevenness was produced on the specimen surface.