What can explain the more weight gain of aluminum coated steel than non-coated steel after NaCl immersion?

I have a 2 week experiment. I put aluminum coated and non-coated steel of the same size and shape in separate beakers with NaCl solution. Both are sealed. But, I am surprised that Al coated steel gained more weight than the non-coated steel after immersion. I know that the weight gain can be attributed to the formation of corrosion products. The measurements shows that the coated steel gained more weight, which be indicates more corrosion. But I'm sure that it doesn't since the liquid solution is still clear without any sign of rust. Unlike on the non-coated steel which has formation of rust that settles at the bottom.


