Influence of copper additions on materials properties and corrosion behaviour of Al-Mg alloy sheet

Additions of a few tenths of a percent of Cu to Al-Mg alloys give rise to a noticeable age-hardening effect. This can be utilized to overcome the softening during paint curing of conventional Cu-free Al-Mg alloys of the AA 5xxx series for car body applications. In the present study we explore this effect in sheet material of the Al-Mg-Cu alloy AA 5023. Mechanical properties and formability of AA 5023 sheet were determined and compared with results obtained in the Cu-free alloys AA 5019 and AA 5182. The resistance to corrosion, viz. general pitting behaviour, filiform corrosion and, most notably, intergranular corrosion was probed. As to the latter, TEM analysis was performed to assess type, composition and spatial arrangement of grain boundary phases causing intergranular corrosion in AA 5xxx series alloys. The results are discussed as a function of alloy composition, recrystallized grain size as well as final heat treatment, i.e. batch annealing vs. continuous solution heat treatment. (C) 2017 Elsevier B.V. All rights reserved.