Aluminizing of plain carbon steel: Effect of temperature on coating and alloy phase morphology at constant holding time

Aluminized steel possesses excellent physical, chemical and mechanical properties as compared to plain carbon steel. This type of steel has found application in high temperature, oxidizing and corrosive environments. In addition, aluminized steel is more cost effective than stainless steels. The objective of the current study is to study effect of temperature on the thicknesses and phase morphology of the coating and intermetallic layer that is formed during hot-dip aluminizing of steel at a constant immersion time of 30 minutes. 1040 steel substrates were aluminized by hot-dipping procedure in pure aluminium and in three different Al-Si alloy melts of varying composition. Hot-dipping was done at three different temperatures mainly at 933, 973 and 1023 K. The steel specimens were held in the melts for 30 minutes after which they were withdrawn from the molten aluminium and allowed to cool to room temperature. The coated samples were then sectioned for metallographic sample preparation. The samples were characterized for thickness of the coating and intermetallic phase thickness and phase composition of both the coating and intermetallic layers. The samples were analyzed by optical light microscope, SEM, EPMA, XRD and micro hardness.The results show that a greater thickness of the coating and intermetallic layer is obtained with increase in immersion temperature. Two different alloy phases are present in samples hot dipped in pure aluminium while three phases are present in the steel samples hot dipped in the three Al-Si alloy melts. The intermetallic layers have higher vickers hardness values than the coating layer and steel substrate and are more brittle