Chapter G.4 - 5XXX series alloys

Abstract

5XXX alloys combine several key properties: a good level of mechanical performance including at cryogenic temperatures, good weldability and very good corrosion resistance to the point of becoming the first choice in sheet metal work for transport and storage (road tankers), and shipbuilding including oil tankers, etc. Industrial wrought alloys rarely contain more than 5 wt.% magnesium because, above this level, the stability of the alloy decreases, especially under the effect of temperature. Most 5XXX series alloys contain other additions such as manganese and chromium, which provide a further increase in tensile strength and/or certain properties including corrosion resistance and weldability. The corrosion resistance of the 5XXX series alloys depends on the level of precipitation of the β-phase, which increases rapidly when: the magnesium content is high, the service operating temperature is elevated, and strain hardening is pronounced. 5XXX series alloys may be susceptible to: localized corrosion, intergranular corrosion, stress corrosion cracking and exfoliation corrosion. Heat treatments carried out during processing can stabilize these alloys by causing a discontinuous ‘pearl necklace’ precipitation of the β-phase at grain boundaries.