Abstract:
The effects of the Cu concentration in Al (2~15 wt. %) on the growth and morphology of
the intermetallic layer, phase constituents, hardness, oxidation and adhesion properties of an
aluminized steel have been examined. In addition, the effects of variation in aluminizing
temperature (675~950 °C) and dipping time (1~10 minutes) on the growth of the
intermetallic layer were investigated. The techniques employed during the investigation
included
optical
microscopy,
scanning
electron
microscopy,
energy dispersive
spectroscopy, X-ray diffraction and thermal gravimetric analysis. The intermetallic layer
formed during aluminizing in pure Al was thick and exhibited a finger-like morphology.
While in the Al-Cu alloys, thickness of the intermetallic layer decreased gradually by
increasing the Cu content from 2-11%. This decrease in thickness was attributed to the
formation of tetragonal phases, Al2Cu and Al7Cu2Fe, on the surface of aluminized steel.
The addition of the Cu content beyond 11% did not reduce thickness of the intermetallic
layer further; however, the finger-like morphology of the intermetallic layer transformed
into smoother one. The thickness of the intermetallic layer increased by increasing the
aluminizing temperatures from 675-775 °C in the pure Al and the Al-Cu alloys, while
above this range it was found constant. Likewise, it increased rapidly by increasing
dipping time up to 4 minutes, after that with increasing time it increased very slowly.
Conversely, the variations in aluminizing temperature and dipping time did not influence
morphology of the intermetallic layer. The hardness of the coating achieved with the
addition of the Cu content in Al was higher than pure Al and Al-Si alloys. However, the
oxidation and adhesion properties of the steel aluminized in the Al-Cu alloys were
comparable with that aluminized in pure Al and Al-Si alloys.
