Hot-Dip Aluminizing with Silicon and Magnesium Addition II. Effect on Corrosion Resistance

The effect of silicon and magnesium addition in a molten Al bath on the morphology and corrosion resistance of the Al coating layer of steel formed during hot-dip aluminizing was investigated at the temperatures of 700, 800, and 900 degrees C for the dipping time of 1-15 minutes. The thickness of the intermetallic layer decreased with an increasing Mg or Si content within a range of 0-1 at%. Addition of Si made the intermetallic layer thin whereas addition of Mg compensated for the decrease of the thickness significantly. The shape of the intermetallic layers became less irregular than that of the hot-dip aluminizing in pure aluminum. The results of immersion corrosion tests and electrochemical corrosion tests in a solution of 3 wt% NaCl showed that the corrosion resistance of the Al-1% Si-1% Mg coated steel had increased significantly over the Al coated steel. The open circuit potential changed from -0.56324 V (vs. SCE) to -0.48872 V (vs. SCE) and the corrosion current density decreased from 9.9991 mu A/cm(2) to 2.1160 mu A/cm(2). A salt fog spray test on these specimens also showed hot-dip aluminizing with Si and Mg addition increased the corrosion resistance significantly.