What Metals Rust Faster in Fresh Water?

Magnesium

• Magnesium is at the top of the Galvanic scale. This scale is used to rate the reactivity of the metals. A high reactivity metal corrodes faster than one of the noble metals, such as gold, platinum and chromium. Magnesium is not often used alone as a structural metal, but it is used in many alloys. It is very light but it is not strong. Magnesium is frequently used with other metals to make aluminum alloys. It does not take much moisture to corrode magnesium, and it happens more quickly than on iron and steel.

Zinc

• Zinc corrodes quickly, but the corrosion is not actually rust. The corrosion on zinc is white at first. It then turns black and finally red, which looks like rust on iron. When wet and deprived of air, zinc corrodes. A freshwater environment is perfect for this scenario.

Iron

• Iron reacts very quickly to water molecules. Rust that develops on iron is called iron oxide because it is the chemical compound formed by iron and oxygen. Iron seems strong and impermeable, but water molecules easily seep into the pores of iron and react to cause rust and corrosion. As iron rusts, it sheds the layer of iron oxide that forms, exposing fresh iron that, in turn, rusts and falls off. This process eventually eats away the iron entirely. The iron content of steel is what causes steel to rust.

Copper

• Copper also corrodes rather than rusts. When exposed to freshwater over long periods of time, it turns dark and eventually green. Copper is relatively high up on the Galvanic scale but is resistant enough to corrosion to be used for some water pipe systems. A small amount of copper is actually necessary for the human body, but large amounts can be harmful. Corroding copper pipes are the number one reason for copper that is found in drinking water supplies, according to the Environmental Protection Agency.