Chapter D.1 - Parameters governing in-service corrosion resistance

Abstract

Corrosion is a complex phenomenon that depends on many environmental, microstructural and service condition parameters. The environment plays a very important role in the corrosion resistance of a metal or alloy. Heat treatment of 2XXX, 6XXX and 7XXX series alloys has a major influence on their corrosion resistance including intergranular corrosion, exfoliation corrosion, stress corrosion, etc. Experience shows that design, often optimized with regard to mechanical properties, and user properties with the right choice of alloys, can, however, neglect certain details that in the short or medium term can prove to be detrimental, or even catastrophic, to corrosion resistance in service. The purpose of this chapter is to examine the influence of various corrosion resistance parameters. Related to the environment: The nature of the environment, concentration, oxygen content, pH, temperature and pressure. Related to the metal: composition, processing methods: direct casting and twin roll casting, heat treatments, grain size, strain hardening and surface condition. Related to assembly methods: assembly methods, arc welding, laser welding, FSW welding and bonding. Conditions of service: contact with other metals, mechanical constraints, design measures, contact with other materials, storage and maintenance. It is also necessary to examine how corrosion resistance can be affected by new processing as twin roll casting and new joining technologies as friction stir welding.