SCC Susceptibility and Formability in Relation to Different TMTs of an Al-6.8 wt% Mg Alloy Sheet

Abstract

The Al-Mg alloy sheets have been increasingly used for automotive and marine applications as they offer good combination of strength, formability, corrosion resistance and weldability [1-4]. High Mg containing Al-Mg alloys, with more than 3.5 wt% Mg, can achieve high strength level through solid solution and strain hardening effect, but they become susceptible to intergranular corrosion (IGC) and stress corrosion cracking (SCC). This susceptibility is caused by Mg-rich β-phase precipitation at grain boundaries that occurs during sensitization treatment (65-180 °C) [5-8]. The degree of susceptibility to IGC and SCC attack can vary depending on the microstructure of Al-Mg alloys. It has shown [9,10] that microstructures with continuous layer of β-phase precipitates along grain boundaries are highly susceptible to IGC and SCC, while uniformly distributed β-phase particles provide good corrosion resistance. Thus, a good balance of strength and corrosion resistance can be achieved by an optimization of the microstructure development. As those high Mg containing Al-Mg alloy sheets are commonly pass through some shaping processes in automotive and shipbuilding industry, the understanding of microstructure - corrosion - formability relationships appears to be very important. Thus, the aim of this paper was to examine the effect of the microstructure developed under different thermo-mechanical treatments (TMTs) on the susceptibility to stress corrosion cracking and formability of a highly alloyed Al - 6.8 wt% Mg sheets.