S.K. Kairy

On the Electrochemical and Quasi In Situ Corrosion Response of the Q-Phase (AlxCuyMgzSiw) Intermetallic Particle in 6xxx Series Aluminum Alloys

The electrochemical response and corrosion associated with the Q-phase (AlxCuyMgzSiw) intermetallic compound was studied. Q-phase intermetallics are the principal strengthening phase in a number of Cu-containing 6xxx series (Al-Mg-Si) alloys, and Q-phase has not previously been uniquely studied in regard to its influence on localized corrosion in detail. Herein, quasi in situ scanning transmission electron microscopy was utilized in understanding the localized corrosion response associated with nanoscale Q-phase precipitates in a Cu-containing 6xxx series Al alloy sheet with a composition (in wt%): 97.3Al-0.9Si-0.74Mg-0.84Cu-0.08Fe-0.14Mn. Furthermore, the Q-phase compound was also produced on the microscale within a bulk-synthesized alloy. The electrochemical behavior of the microscale Q-phase was studied using a micro-electrochemical capillary cell and by potentiodynamic polarization. Quasi in situ scanning electron microscopy was also performed on the bulk alloy synthesized to contain microscale Q-phas...

Understanding the Origins of Intergranular Corrosion in Copper-Containing Al-Mg-Si Alloys

A definitive understanding of the mechanism of intergranular corrosion (IGC) in under-aged (UA) Cu-containing Al-Mg-Si alloys has not been clear to date. The grain boundary microstructure and chemistry in an UA Cu-containing Al-Mg-Si alloy were characterized by coupling atom probe tomography and scanning transmission electron microscopy. The rapid formation of an ultra-thin wetting Cu layer and discrete Q-phase (Al4Cu2Mg8Si7) precipitates along the grain boundaries, and a precipitate-free zone adjacent to the grain boundaries in the UA condition contribute to IGC.

Evolution of Grain Boundary Precipitates in an Al-Cu-Li Alloy During Aging

The grain boundary microstructure of Al-Cu-Li alloy AA2050 was investigated for different isothermal aging times to rationalize intergranular corrosion (IGC) characteristics. In the underaged condition, the dominant grain boundary precipitates are fine T1 (Al2CuLi). Extended aging revealed that grain boundaries were decorated by large T1 precipitates and S′ phase (Al2CuMg), with S′ growth not dimensionally constrained. Such a transition in the precipitate type at grain boundaries is a unique feature of the Al-Cu-Li system.

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

The metastable pitting of 6xxx series aluminum alloys (Al-Mg-Si-(Cu)) as a function of Cu content and aging was studied. Potentiodynamic polarization and potentiostatic transients were performed to...

On the Intergranular Corrosion and Hardness Evolution of 6xxx Series Al Alloys as a Function of Si:Mg Ratio, Cu Content, and Aging Condition

The intergranular corrosion (IGC) and hardness associated with 6xxx series aluminum alloy sheets, varying in composition (namely Si:Mg ratio and Cu content), were systematically studied in four different aging conditions. The IGC of each alloy was studied using ASTM G110, scanning electron microscopy, and optical microscopy. Scanning transmission electron microscopy was also used to rationalize the grain boundary chemistry of the relevant alloys. It was revealed that the severity of IGC depends on the continuity and type of grain boundary phases. The property space reported herein reveals prospects for the optimization of 6xxx series alloy compositions.