Localized Intergranular Corrosion Research Articles

Influence of Ageing on the Intergranular Corrosion of an Al–Mg–Si Alloy

This report investigates the influence of ageing on the susceptibility to intergranular corrosion (IGC) of an Al–Mg–Si alloy. The selected AA6063 Al-alloy has been exposed to ageing treatments at a predetermine temperature of 423 K for durations of 1 to 168 h to achieve the wide range of ageing states covering under- to peak- to over-aged. The ageing behaviour of the selected alloy has been determined based on the results of hardness and tensile properties. The susceptibility to IGC has been evaluated following the British standard (BS ISO-11846) method B and assessed based on the average and maximum corrosion depths apart from in-depth surface and sub-surface characterizations of corroded specimens. It has been observed that the depths of corrosion increase monotonically with increase in ageing time. With progress of artificial ageing, the dominant mode of corrosion gradually changes in the order of minor pitting, moderate pitting, pitting plus localized IGC, localized IGC and uniform IGC. The phenomenon of preferential dissolution of Mg from the β″ (Mg5Si6) and β (Mg2Si) precipitates as well as the existence of Fe-rich intermetallic particles at the grain boundaries cause the pitting and intergranular corrosion because of the formation of local galvanic cells between the lower corrosion potential of Mg-depleted precipitates or precipitate free zones and to the adjacent anodic grain boundary precipitates.

Optimizing the Plasma Arc Welding Process Parameters to Attain the Minimum Corrosion Rate in the AISI 409M grade Ferritic Stainless Steel Autogenous Joints

Abstract The combination with good mechanical properties and manufacturing characteristics, makes stainless steel an indispensable tool for the designer. Stainless steels become susceptible to localized intergranular corrosion when chromium carbides form at the grain boundaries during high temperature exposure. This depletion of chromium at the grain boundaries is termed ‘sensitization’, because the alloys become more sensitive to localized attack in corrosive environments. Stainless steels like AISI 409M grade, which are having low chromium content (approximately 11%), are susceptible to localized corrosion. The susceptibility of these alloys are strongly affected by welding processes and filler metals, which change the microstructure of the alloy in order to have optimum mechanical properties. Hence, the present investigation has been carried out to understand the effect of Plasma Arc Welding (PAW) process on pitting corrosion behavior of AISI 409M grade stainless steel joints. Also, the PAW process parameter such as welding speed, voltage, heat input were optimized with help of Response Surface Methodology (RSM) to attain the maximum tensile strength and minimum corrosion rate in the welded joints.

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 448 K (175 °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.

Correlation between artificial aging and intergranular corrosion sensitivity of a new Al‐Cu‐Li alloy sheet

The intergranular corrosion (IGC) sensitivity of an Al‐3.81Cu‐1.28Li‐X alloy with T6 aging for different time at 150, 175, and 200 °C was investigated. With aging, the alloy potential lowers due to precipitation, accompanied with coarsening and discontinuous distribution of grain boundary precipitates, which contributes to corrosion evolution with aging time. Corrosion mode evolution with aging stage (corresponding to hardness evolution) at aging temperature of 150 and 175 °C follows the following order: pitting and local IGC (early aging), general IGC (under‐aged), local IGC with pitting (near peak‐aged), and pitting (over‐aged). At elevated aging temperature of 200 °C, the corrosion mode evolves much faster. IGC only appears in the intensively under‐aged stage, but the later under‐, peak‐, and over‐aged stage are featured with pitting corrosion. As IGC occurs, its depth is initially increased and then decreased with aging time.

Intergranular corrosion of Zn-free and Zn-microalloyed Al–xCu–yLi alloys

The influence of 0.42 and 0.72wt.% Zn on the intergranular corrosion (IGC) of Al–3.7Cu–1.15Li–0.5Mg and Al–2.7Cu–1.7Li–0.3Mg alloys (representing different Cu/Li ratios) was investigated. IGC dependence on ageing time was studied and a primitive IGC diagram established. With ageing, the potential of the Al–xCu–yLi alloys lowered due to precipitation, accompanied by grain boundary precipitate coarsening. Concomitantly, corrosion mode evolved with ageing from pitting and local IGC (early ageing), general IGC (under-aged), local IGC (near peak-aged) and pitting (over-aged). Of key interest is that Zn additions remarkably decreased the IGC sensitivity of the Al–2.7Cu–1.7Li–0.3Mg.

Corrosion Fatigue Behavior of 7A85 Aluminum Alloy Thick Plate in NaCl Solution

The S–N curves of 7A85-T7452 aluminum alloy in laboratory air and in neutral 3.5 wt% NaCl solution were obtained by axial fatigue tests. Results show that the detrimental effect of the aggressive solution was not noticeable at high-cyclic-stress regions, but the effect was significant at low-stress region. Corrosion fatigue mechanism was discussed by corrosion morphology analysis, fracture surface analysis and microstructure characterization. It was found that the corrosion fatigue crack commonly initialed at the localized intergranular corrosion site. TEM analysis showed that the microstructures of 7A85-T7452 aluminum alloy were characterized by fine and homogeneously distributed matrix precipitates, as well as continually distributed anodic grain boundary precipitates. The types of microstructures are the reason for its intergranular corrosion susceptibility. The corrosion fatigue process of 7A85 aluminum alloy in 3.5 wt% NaCl solution can be divided into four stages: the crack initiation stage, the stable growth stage with low and high growth rate and the final rupture stage. The sodium chloride solution mainly affected the crack initiation stage and the stable growth stage with low growth rate, and when the crack growth rate reached a threshold, the effect was reduced.

Effect of Artificial Aging on Salt Spray Corrosion Resistance of 2024 Al Alloy

The effect of artificial aging on the corrosion resistance of 2024 Al alloy was investigated by field emission scanning electron microscope (FE-SEM) and accelerated corrosion test. For comparison, the solution treatment followed by air-cooled and water-quenched samples were also researched. Accelerated corrosion test revealed that the corrosion resistance of the alloy strongly depended on artificial aging times, and the weight gain of the aged alloy increased first and then decreased with increasing the aging times, and a maximum value was found at peak aged condition. The air-cooled sample had the highest weight gain while the water-quenched one had the lowest weight gain among all the samples. The corrosion morphologies showed that pitting and localized intergranular corrosion were the main corrosion forms for the air-cooled and aged 2024 Al alloys. However, only pitting corrosion took place on the water-quenched samples. The pitting and intergranular corrosion resulted from galvanic corrosion between secondary particles and matrix Al, and between grain boundary precipitates and matrix Al, respectively.

Mechanical Property and Intergranular Corrosion Sensitivity of Zn-Free and Zn-Microalloyed Al-2.7Cu-1.7Li-0.3Mg Alloys

The influence of 0.72 pct Zn addition on the tensile properties of Al-2.7Cu-1.7Li-0.3Mg alloys was investigated. Their intergranular corrosion (IGC) dependence on aging [T6 type at 423 K (150 °C) and 448 K (175 °C) and T8 type at 423 K (150 °C)] time was studied. An IGC diagram associated with aging process was established. The addition of 0.72 pct Zn enhanced the strength of the Al-Li alloy with T6 type aging at 448 K (175 °C). With aging process, the corrosion mode of the T6-aged Al-Li alloys was changed in the following order: pitting and local IGC (initial aging stage), general IGC (underaging stage), local IGC (near peak-aging stage), and pitting (overaging stage) again. The IGC depth was increased first and then decreased with aging time extension. The corrosion potential change of grains and the microstructure variation were used to explain the IGC sensitivity of the Al-Li alloy with different tempers. Meanwhile, 0.72 pct Zn addition decreased the IGC sensitivity of the Al-Li alloy, especially the T6-aged Al-Li alloy.

Mechanical Property and Intergranular Corrosion Sensitivity of Al-2.7Cu-1.7Li-0.3Mg Alloy with Small Zn Addition

The influence of aging (T6 at 150°C and175°C, T8 at 150°C) and 0.72% Zn addition on the mechanical properties, microstructures and intergranular corrosion (IGC) behavior of Al-2.7Cu-1.7Li-0.3Mg alloys was investigated. With 0.72% Zn addition, the strength of the Al-Li alloy was increased. As the aging time was extended, the corrosion type of the studied Al-Li alloys was changed in the following order: pitting, local IGC, general IGC, local IGC and pitting again. For the T6 temper, as the aging temperature was elevated from 150°C to 175°C, the aging time period for IGC appearance was shortened. The pre-deformation before aging (T8 temper) also greatly shorten the aging time period for IGC. Meanwhile, the addition of 0.72% Zn decreased the IGC sensitivity and shortened the aging time period for IGC.

Sulfide Induced Intergranular Corrosion of Copper in Salt Water Containing Benzotriazole

This paper investigates the effect of pretreatment with benzotriazole on the corrosion of copper in sulfide polluted salt water. The treatment of copper in the presence of benzotriazole under a mild oxidizing potential reveals the remarkable inhibition efficiency of BTAH reflected in a passive current of less than 0.1 μA cm-2 after one hour. Upon injection of 10-3 M HS-, a rapid increase in current to about 200 μA was obtained. The current jump seen after injection of sulfide ions is due to localized intergranular corrosion as shown by the scanning electron microscopy (SEM) examination. Copper suffered only localized corrosion occurred at the grain boundaries while the grain surfaces remained well protected. Under this condition, sulfur was detected using energy dispersive spectroscopy (EDS) at the grain boundaries, but not on the grain surfaces. X-ray photoelectron spectroscopy revealed the presence of sulfide ions and BTAH on the corroded surface. [DOI: 10.1380/ejssnt.2011.306]

Effect of Heat Treatment on Grain Boundary Nanostructure and Corrosion of Low Copper AlMgSi Alloy

AlMgSi (6000-series) aluminium alloys are generally known to be re-sistant to intergranular corrosion (IGC). However, unfavourable alloy-ing and thermomechanical history may introduce susceptibility to IGC. A model alloy in the 6000-series, with 0.2 wt% Cu, was studied using an accelerated corrosion test. In the naturally aged T4 temper, the ma-terial did not exhibit localized corrosion, while in the underaged state (below peak strength), the alloy became highly susceptible to IGC. Samples aged to peak strength T6 temper or overaged were nearly re-sistant to IGC, exhibiting only shallow, localized IGC and pitting. TEM investigation of the IGC-susceptible material revealed nanosize AlMgSiCu particles along the grain boundaries, along with Cu-enriched nanofilm connecting the particles, indicating the cause of sharp IGC propagation. Further ageing caused coarsening of the grain boundary film thereby destroying its continuity and giving increased resistance against IGC.

The effects of electropolishing (EP) process parameters on corrosion resistance of 316L stainless steel

Improvement of the corrosion resistance capability of a workpiece being processed by the electropolishing (EP) is one of the most importance process characteristics. In this paper, the effects of the EP process parameters on the corrosion resistance performance of the SS 316L stainless steel were studied based on the uniform and localized intergranular corrosion (IGC) analyses. The IGC is the prominent characteristics of localized corrosion in stainless steel.The workpiece (anode) material was the SS 316L stainless steel. The cathode material under study was platinum. The electrolyte was composed of sulfuric acid, phosphoric acid, glycerin and DI water. The test specimens were all polished before experiments in order to reduce the effect of the bailby layer. Variables of the EP process parameters gap between the electrodes and the process time.The specimens were analyzed, first, by the surface roughness measurement. Secondly, they were observed under the optical microscope for surface marks and defects. It was followed by the linear polarization analysis for the uniform corrosion performance. The electrochemical potentiokinetic repassivation (EPR) test was employed to study the localized, IGC. Finally, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses were conducted to analyze the metallurgical composition and the thickness of the passive film. The results showed that the EP process greatly improved the corrosion resistance of the SS 316L stainless steel.

Corrosion behavior of a welded stainless-steel orthopedic implant

The corrosion behavior of combinations of materials used in an orthopedic implant: the spherical part (forged or forged and annealed) constituting the head, the weld (tungsten inert gas (TIG) or electron beam (EB) techniques), and the cylindrical part (annealed) constituting the shaft of a femoral prosthesis – has been investigated. Open-circuit potentials, potentiodynamic curves, Tafel slope, mixed potential theory and susceptibility to intergranular attack are electrochemical and chemical procedures selected for this work. Electrochemical measurements using a microelectrode have been made in the following zones: spherical part, cylindrical part, weld, and weld/sphere, and weld/shaft interfaces. To detect intergranular attack, the Strauss test has been used. At the interfaces, corrosion currents, measured ( I corr) and predicted ( I couple) are low, in the order of the pico- to nanoampere. The electrochemical behavior of the electron beam (EB) weld is better than that of the tungsten inert gas (TIG). Welds at interfaces can behave either anodically or cathodically. It is better if welds, which are sensitive parts of the femoral prosthesis, behave cathodically. In this way, the risk of starting localized corrosion (pitting, crevice or intergranular corrosion) from a galvanic couple, remains low. From this point of view, the sample with the EB weld offers the best behavior. All the other samples containing a TIG type of weld exhibit a less favorable behavior. The mechanical treatments (forged, and forged and annealed) of the steel sphere did not show any difference in the corrosion behavior. No intergranular corrosion has been observed at the weld/steel interface for unsensitized samples. With sensitized samples, however, a TIG sample has exhibited some localized intergranular corrosion at a distance of 500 μm along the weld/stainless steel (sphere) interface.