Aluminium is a highly reactive material. In most surroundings, inside or in the open air, Aluminium has a very high resistance to corrosion. It rapidly forms a thin and dense oxide layer that protects the underlying material very well. The presence of the oxide layer makes aluminium very suitable for many applications. But some environments aluminium may show corrosion behaviour. This section will explain in detail the principles of aluminium corrosion and surface engineering that will enable the right use of aluminium in the right place.

Rust is the common term for corroded steel or iron. The reddish oxide produced is caused by oxygen and moisture. Hydrated Iron(III) Oxide, or rust, has become a problem with the increased use of iron and steel for building purposes today,  Rust is the common term for corroded steel or iron. It is a reddish-brown solid that weakens the iron or steel and can cause it to break and forms when iron is exposed to oxygen and water, the oxygen being found in the air, and the water being found in a variety of different forms, for example, rain, condensation and water vapour in the surrounding air.

Corrosion is derived from the Latin "corrosus" meaning gnawed away.  Corrosion may be further defined as a gradual destruction of a material, a substance, or an entity, usually by solution or other means attributed to a chemical process. Many different corrosion mechanisms exist. The most common types are generally well understood. For each, the process is complex, incorporates many factors, and varies according to metal and specific operating conditions.

Iron and steel, the most commonly used metals, corrode in many media including most outdoor atmospheres. Usually they are selected not for their corrosion resistance but for such properties as strength, ease of fabrication, and cost. These differences show up in the rate of metal lost due to rusting. All steels and low-alloy steels rust in moist atmospheres. In some circumstances, the addition of 0.3% copper to carbon steel can reduce the rate of rusting by one quarter or even by one half.

Pitting is used to describe the formation of small pits on the surface of a metal or alloy. Pitting corrosion is a very severe form of localised corrosion. A characteristic of pitting is that only small spots on the metal surface corrode, but due to the small ratio of the anodic on cathodic surface area, the corrosion pits can grow quickly resulting ultimately in perforation of the metallic structure.

Erosion corrosion is the corrosion of a metal which is caused or accelerated by the relative motion of the environment and the metal surface. It is characterized by surface features with a directional pattern (comet tails, horseshoe marks, etc) which are a direct result of the flowing media. Erosion corrosion is most prevalent in soft alloys (i.e. copper, aluminum and lead alloys).

One type of corrosion that is often overlooked in the moldmaking industry is galvanic corrosion. Sometimes it is identified wrongly as electrolysis. Galvanic corrosion refers to the damage induced when two dissimilar metals are coupled in a corrosive electrolyte. When this occurs, the less noble (less able to resist this type of corrosion) of the metals in the reaction becomes the anode (positive) and corrodes more quickly than it would by itself, whereas the more noble metal becomes the cathode (negative) and corrodes more slowly than it would alone.

Sometimes Intergranular corrosion is also called intercrystalline corrosion or interdendritic corrosion. In the presence of tensile stress, cracking may occur along grain boundaries.This type of corrosion is frequently called interranular stress corrosion cracking (IGSCC) or intergranular corrosion cracking.

Crevice Corrosion refers to the localized attack on a metal surface at, or immediately adjacent to, the gap or crevice between two joining surfaces. The gap or crevice can be formed between two metals or a metal and non-metallic material. Outside the gap or without the gap, both metals are resistant to corrosion. Crevice corrosion is not unique to stainless steels. It can occur in other alloys including those of aluminium, titanium and copper.

Rust is the common term for corroded steel or iron. It is very common compound, iron oxide. Iron oxide, the chemical Fe2O3, is common because iron combines very readily with oxygen. It is so readily that pure iron is only rarely found in nature. The reddish oxide produced is caused by oxygen and moisture.

Pitting is used to describe the formation of small pits on the surface of a metal or alloy. Pitting is suspected to occur in much the same way crevice corrosion does, but on a flat surface.  A small imperfection in the metal is thought to begin the process, then a "snowball" effect takes place. Pitting can go on undetected for extended periods of time, until a failure occurs. Stainless steel to a chloride containing stream such as seawater, Pitting would overrun the stainless steel in a matter of weeks due to it's very poor resistance to chlorides, which are notorious for their ability to initiate pitting corrosion.

A cathodic protection system is a corrosion cell in which the structure to be protected is the cathode. Sacrificial or galvanic systems are corrosion cells of the differential metal type. The earliest experiments on cathodic protection were performed with zinc anodes that were electrically connected to copper plates immersed in seawater. From galvanic series, an arrangement would produce a cathode (copper) and an anode (zinc). In the large galvanic cell so formed, the zinc cylinder corroded away in a manner to protect the copper substrate. This method of cathodic protection can be used with other combination of metals providing the necessary current to the metal to be protected.

Galvanic corrosion refers to corrosion damage induced when two dissimilar materials are coupled in a corrosive electrolyte.

 (ICCP)
Cathodic protection can be applied if the metal to be protected is coupled to the negative pole of a direct current source (schematic), while the positive pole is coupled to an auxiliary anode. Since the driving voltage is provided by the DC source there is no need for the anode to be more active than the structure to be protected.