SENSITIZATION AND SCC BEHAVIOUR OF AA5059 & AA5083 ALLOYS

Abstract

Sensitization is a most common phenomenon observed in 5xxx (Al-Mg based) series aluminium alloys. Sensitization occurs when 5xxx aluminium is repeatedly exposed to high temperatures, causing the magnesium in the alloy to move near the grain boundaries. When the magnesium precipitate creates a continuous network surrounding the grains, this migration finally develops a corrosion cell, which leads to inter-granular corrosion (IGC). The magnesium precipitate is nothing but β-phase (Mg2Al3), which is electrochemically active and may preferentially dissolve. The non-heat treatable aluminium alloy AA5083 (Al-4.4Mg-0.7Mn-0.15Cr) which is suitable for marine applications is noted for its exceptional corrosion resistance. This work examines the behaviour of the marine-grade aluminium alloy when subjected to sensitization toward stress Corrosion Cracking (SCC) and compares it to that of the AA5059 which is of higher strength. AA5059 aluminium alloy samples are artificially sensitized at various temperatures for various durations of time, followed by Constant Load Test (CLT). The result in this report shows that the DoS (degree of sensitization) increases considerably, when exposed to elevated temperatures ranging from 80 °C to 200 °C for extended periods of time. It can develop intergranular stress corrosion cracking (IGSCC). Also the fracture due to SCC in simulated sea water (3.5 wt% NaCl solution) after different sensitization times and temperature conditions is studied.