Structure-property correlation in aluminized coatings

Mild Steel, on hot dip aluminizing, develops a coating which reveals a soft, outer Al layer followed by a soft (Fe3Al) and then hard intermetallic (FeAl3, Fe2Al5) bearing) layers. In order to improve wear resistance and thermal stability of coatings, diffusion annealing was done at 773-923 K, resulting in a phase transformation on the surface i.e. Al ®FeAl3 ® FeAl3 + Fe2Al5 ® Fe2Al5. These phases, though not favourable from the point of view of Pilling-Bedworth's condition, nevertheless, give adherent and bendable-coated surfaces, which are not susceptible to thermal shock.