This is the first edition of A Guide to Corrosion Protection - Passenger Car and Light Truck UnderbodyStructural Components, written and published by the Light Truck Frame Project Team of the Auto/SteelPartnership (A/SP). The publication brings together basic corrosion conditions, materials, coatings, manufacturing processes,design considerations, test methods and “lessons learned”. It has been prepared to meet the needs of OEM engineers. It is also intended to meet the needs of the Tier 1 and 2 suppliers of underbody components and steel industry marketing and technical personnel. As experience in its use is gained, revisions and additions will be issued. Types of Corrosion. Four types of corrosion are relevant to underbodystructural components: crevice, pitting, galvanic and cosmetic. Crevice corrosion is often associated with small volumes of stagnant solutionor electrolyte trapped in crevices of joints or in surface deposits and poultices. Pitting corrosion isa localized attack, usually caused by chlorides aspits form, resulting in a roughened surface.Crevice and pitting corrosion can lead to steel perforation and premature functional failures.Galvanic corrosion occurs when dissimilar metalsare in contact with one another. For example, an aluminum component in contact with a steelcomponent may corrode, or sacrifice itself, to protect the steel component. Corrosion that initiates on a visible surface of a vehicle, usually at nicks or scratches in a post-coating, is calledcosmetic corrosion. In most instances, cosmeticcorrosion is an appearance issue; however, it canlead to damage including perforation.