The Influence of Copper Additions and Aging on the Microstructure and Metastable Pitting of Al-Mg-Si Alloys

Abstract

The metastable pitting of 6xxx series aluminium alloys (Al-Mg-Si-(Cu)) as a function of Cu content and ageing was studied. Potentiodynamic polarisation and potentiostatic transients were carried out to determine the electrochemical response of a family of 6xxx alloys based on a similar Si:Mg ratio. Additionally, the evolution of microstructure in all samples studied was also determined using transmission electron microscopy. The refinement in thickness of precipitates with the addition of Cu was shown to decrease the propensity for metastable pitting.

Improved Corrosion Resistance of Aluminum Brazing Sheet by a Post-Brazing Heat Treatment

“…classic IGC of the as-brazed aluminum components due to profusion of local micro-galvanic cells overruling the conventional grain boundary solute enrichment process and the adjacent relatively precipitate-free grains [27][28][29] . Other studies on AlMgSiCu alloys evaluate the effects of heat treatments on micro-galvanic coupling between grain boundary precipitates and the depleted zones 24,25,30 .…”

Galvanic coupling effects on the corrosion behavior of the 6061 aluminum alloy used in research nuclear reactors

“…Kairy et al [10] showed that depending on the continuity and type of grain boundary phases, which is dependent on the chemical composition and aging parameters, the severity of intergranular corrosion (IGC) associated with 6XXX series aluminum alloy varies. In another study, the authors [11] reported that susceptibility to metastable pitting of 6XXX Al series is reduced with the refinement of precipitates. Galvanic corrosion occurs when dissimilar metals with different potentials are coupled and exposed to corrosive environments.…”

“…The effect of thermomechanical treatments on the corrosion behavior of Al alloys has been extensively reported [8][9][10][11]. According to Zeid et al [9], the  (Mg2Si) phase formation in the 6061 alloy, after natural and artificial aging, can assume different orientations and this can affect the corrosion behavior of the alloy.…”

Unravelling the characteristics of Al-alloy corrosion at the atomic to nanometre scale by transmission electron microscopy

“…Precipitation hardenable aluminium (Al) alloys such as 6xxx (Al-Mg-Si-(Cu)), 2xxx (Al-Cu-(Mg)) and 7xxx (Al-Zn-Mg-(Cu)) are strengthened by alloying additions and heat treatment processes that cause evolution of nanoscale precipitates in the Al-matrix [1][2]. However, such microstructures, which are intentionally generated for increasing strength, notably deteriorate the localised corrosion resistance of the alloys [1][2][3][4][5]. Nanoscale precipitates exhibit electrochemical characteristics that are different from the Al-matrix, resulting in the selective dissolution of precipitates or the surrounding Al-matrix, leading to pitting and/or intergranular corrosion (IGC) [3][4][5][6][7].…”

“…However, such microstructures, which are intentionally generated for increasing strength, notably deteriorate the localised corrosion resistance of the alloys [1][2][3][4][5]. Nanoscale precipitates exhibit electrochemical characteristics that are different from the Al-matrix, resulting in the selective dissolution of precipitates or the surrounding Al-matrix, leading to pitting and/or intergranular corrosion (IGC) [3][4][5][6][7]. The extent of localised corrosion experienced by different Al-alloys is dependent on the type (and composition) of precipitates within the alloy, and therefore, a definitive understanding of the role of specific nanoscale precipitates in the localised corrosion of Alalloys is essential.…”