R. Zhang

Quantification of Sensitization in AA5083-H131 via Imaging Ga-Embrittled Fracture Surfaces

Sensitization of 5xxx series Al alloys involving precipitation of β phase (Mg2Al3) at grain boundaries was studied for different exposure times at 100°C upon AA5083-H131 (UNS A95083). In this work, we reveal that fracture surfaces prepared by liquid gallium embrittlement can yield a quantification of grain boundary β phase with significant statistics on β phase size and spacing. This information is a necessary first step toward development of quantitative damage models to describe inter-granular corrosion (IGC) and stress corrosion (IGSCC).

A survey of sensitization in 5xxx series aluminum alloys

The 5xxx series (Al-Mg-based) aluminum alloys suffer from intergranular corrosion and intergranular stress corrosion cracking when the alloy has become “sensitized.” Sensitization refers to insidious precipitation of β phase (Mg2Al3), which is problematic when present at grain boundaries. The β phase is electrochemically active and may preferentially dissolve. This paper reviews the relevant works that have documented the degree of sensitization for various 5xxx series alloys, providing a holistic overview of the issue, along with attention to the bulk composition, heat treatment, and microstructure.

Imparting Sensitization Resistance to an Al-5Mg Alloy via Neodymium Additions

Low-level Nd additions, up to 0.17 wt%, were added to Al-5Mg to explore the impact on the subsequent degree of sensitization. Following heat treatment at 150°C for 1 day and 7 days, nitric acid mass loss (NAMLT) tests revealed that additions of >0.11% Nd were effective at decreasing the amount of subsequent intergranular attack.

The Influence of Grain Size and Grain Orientation on Sensitization in AA5083

Aluminum alloy AA5083 specimens (with a nominal composition of Al-4.4Mg-0.5Mn) from the same original plate were prepared with a variation in grain size imparted by cold rolling, cryo-rolling, equal channel angular pressing and high-pressure torsion. Electron backscatter diffraction was used to determine the grain size and misorientation. The effect of grain size on the degree of sensitization for AA5083 was studied via the ASTM G67 nitric acid mass lost test, upon specimens artificially sensitized at 150°C for 7 d. It was revealed that the intergranular corrosion caused by sensitization in AA5083 was significantly influenced by the grain size and processing methods used for grain refinement.

Influence of Mg Content on the Sensitization and Corrosion of Al-xMg(-Mn) Alloys

The influence of Mg content on the degree of sensitization (DoS) of Al-xMg-0.5Mn (wt%) alloys (where x varies from 3.36 wt% to 8.85 wt%) was investigated via the nitric acid mass loss test (NAMLT)....

Theoretical Study of the Influence of Microalloying on Sensitization of AA5083 and Moderation of Sensitization of a Model Al-Mg-Mn Alloy via Sr Additions

The calculated effect of a range of quaternary alloying additions to aluminum alloy (AA)5083 (Al-4.4Mg-0.5Mn [UNS A95083]) was investigated. Attention was given to the influence of composition on the volume fraction of β-phase (Mg2Al3), and the possible formation of any additional phases (which we term γ-phase herein). Alloying additions of silver, cerium, copper, lithium, neodymium, nickel, scandium, silicon, strontium, yttrium, zinc, and zirconium were studied in hypothetical additions of 0.1 wt% and 0.5 wt%, revealing that there is potential to modify the fraction of β-phase, and hence sensitization, in AA5083. Calculations indicated strontium to be the most effective addition in decreasing β-phase fraction during thermal exposure (sensitization); therefore, the influence of Sr additions were studied empirically via production of custom Al-Mg-Mn alloys. Sensitization was investigated via the nitric acid mass loss test (NAMLT), revealing that mass loss from intergranular corrosion decreased by more than...

Influence of microalloying additions on Al-Mg alloy. Part 2: Phase analysis and sensitisation behaviour

Abstract A range of alloys based on the Al-4Mg-0·4Mn system were produced with selected quaternary microalloying additions. In Part 1 of this study, the electrochemical and corrosion response was studied. To characterise the sensitisation behaviour of these alloys, where sensitisation is the major mode of degradation of 5xxx alloys, heat treatment at 150°C was carried out and followed by the Nitric Acid Mass Loss Test (NAMLT) according to ASTM G67-04. Herein the alloying elements studied include silicon, zinc, titanium, zirconium and strontium. The results indicate that strontium (Sr), silicon (Si) and titanium (Ti) have a significant influence in reducing intergranular corrosion (IGC) susceptibility.

Impact of Annealing Prior to Solution Treatment on Aging Precipitates and Intergranular Corrosion Behavior of Al-Cu-Li Alloy 2050

The influences of annealing prior to solution treatment on the grain structure, subsequent aging precipitates, and intergranular corrosion (IGC) of Al-Cu-Li alloy (AA2050) sheet with T6 aging at 448xa0K (175xa0°C) were investigated. Annealing impedes the full recrystallization during solution treatment, increasing the population density of T1 (Al2CuLi) precipitates, but decreasing that of θ′ (Al2Cu) precipitates, of the aged alloy. Meanwhile, annealing leads to the heterogeneous distribution of T1 precipitates, increasing the alloy hardness, and decreasing the open-circuit potential of the aged alloy. With prolonged aging time, the corrosion mode of the aged AA2050 samples with and without annealing evolved in a similar manner. The corrosion mode as a function of aging may be summarized as local IGC with pitting and general IGC with pitting (following initial aging and under the underaged condition), pitting corrosion (later in the under-aging stage), pitting with slight IGC (near the peak-aged condition), and pitting with local IGC (under the overaging condition). The annealing treatment hinders IGC propagation on the rolling surface while accelerating the IGC on transverse surfaces.