Exfoliation Corrosion Behavior Research Articles

Exfoliation behavior of EN AW 7020 with T6, step aging and ultrasonic impact peening processes

Abstract In this study the effect of T6 heat treatment, two-step aging treatment and ultrasonic impact peening on the exfoliation corrosion behavior of welded EN AW 7020 was investigated. Exfoliation tests were performed according to the ASTM G34-01 standard. As expected, as a result of the tests, the base material region of all three samples were showed better corrosion resistance than the heat-affected region. Ultrasonic impact peening and two-step aging treatment was observed that improved EXCO sensitivity in the weld area. When sorting was made by considering the resistance to corrosion of the heat affected zone of the samples, it was observed that the best resistance was shown by the sample with two-step aging treatment, and the worst resistance was shown by the sample with T6 heat treatment.

Exfoliation corrosion susceptibility on friction stir welded aluminium 6061/Cr2O3 composite

The current study investigates the exfoliation corrosion behavior of friction stir welded aluminum composite. The stir casting method was employed to fabricate chromium oxide (2 and 4% wt) reinforced Al 6061 composites. The fabricated composite samples are friction stir welded with two process parameters. The solution immersion tests were performed for two intervals per the ASTM G34 (24 h, 48 h), and the weight loss method was employed. The corrosion sample is analyzed by optical microscope FESEM and surface roughness. The gelatinous corrosion product formed over the surface can apply pressure over the grains resulting in the formation of pits. The intergranular corrosion (IGC) is formed by continuous penetration of the solution and the pits. The grains suffering from IGC are more susceptible to pit. The weight-loss method is not sufficient to predict the damage induced by the exco solution. Evaluating the pit depth can help to know the severity of corrosion. The measurement of the pit is difficult due to its irregular nature. The surface roughness instrument is used, and the damage is represented in average roughness (Ra) and average depth (Rz). The exposure duration and welding parameters play a significant role in corrosion. More material is lost at higher process parameters and extended hours of the test, forming higher surface deterioration.

Quench-induced contributions of high angle grain boundary and low angle grain boundary to exfoliation corrosion propagation in an AlZnMgCu alloy

The exfoliation corrosion behavior of an AlZnMgCu alloy extruded plate subjected to different quenching rates has been investigated. With the decrease of quenching rate, the number of corroded low angle grain boundaries (LAGBs) gradually increases in addition to high angle grain boundaries (HAGBs), leading to rapid development of corrosion along the thickness direction. Consequently, the corrosion morphology changes from layered features to wavy features. The reason has been discussed based on the quench-induced change of precipitation features at HAGBs and LAGBs.

The effect of various RRA treatments on the strength and corrosion behavior of a new type of Al–Zn–Mg–Er–Zr alloy

AbstractThe effect of various retrogression and reaging (RRA) treatments on the strength and corrosion behavior of a new type of Al–Zn–Mg–Er–Zr alloy has been investigated by hardness testing, tensile testing, and evaluating the intergranular corrosion (IGC) and exfoliation corrosion (EXCO) behavior. The results show that the RRA treatment can effectively improve the IGC and EXCO resistance by sacrificing less strength due to the formation of grain interior precipitates and the grain boundary precipitates similar to the T6 temper and T73 temper, respectively. At the peak value of the hardness, the alloy retrogressed at 190°C shows the better IGC and EXCO resistance; the alloy retrogressed at 170°C exhibits the higher strength. The optimal combination of strength, IGC and EXCO resistance is obtained after retrogression at 180°C for 60 min. For the different heat‐treatment tempers, the corresponding microstructure evolution of the precipitates, including Al3(Er,Zr) particles is discussed in detail.

Computational and Experimental Insights into the Role of Acidic Molecules on the Corrosion Behavior on 7A46 Aluminum Alloy.

The corrosion mechanisms for different corrosive media on the aged 7A46 aluminum alloy were systematically investigated at nanoscale level. The combination of empirical intergranular and exfoliation corrosion behavior was employed, and coupled with first-principles calculations. Results revealed that the dispersed distribution of matrix precipitates (MPs) leads to the enhancement of the corrosion resistance pre-ageing (PA) followed by double-ageing (PA-DA) alloy. The deepest corrosion depth of PA-DA alloy was in hydrochloric acid, and the calculation result demonstrates that the passivation effect in combination with the accumulation of corrosion products in nitric acid protect the PA-DA alloy from further corrosion.

The Influence of Introduced Strains on the Exfoliation Corrosion Behavior of Mg-14mass%Li-1mass%Al Alloy

Mg-Li alloys have much better formability than traditional Mg alloys. However, the corrosion resistance of Mg-Li alloys are low due to Li addition and cold-worked Mg-Li alloys sustain exfoliation corrosion, which is serious problem for practical use of Mg-Li alloys [1]. According to our previous report, the elongated grains may be the cause of the exfoliation corrosion. In this study, the exfoliation corrosion behavior of Mg-14mass%Li-1mass%Al (LA141) alloy processed by equal channel angular extrusion (ECAE) is characterized to see the corrosion morphology of the samples introduced more grains than rolling. The specimens processed by rolling showed only elongated grains and the ones processed by ECAE (Route A) at 2 and 4 times showed elongated grains and partially equiaxial grains and in the samples fabricated by ECAE (Route Bc) at 2 and 4 times, equiaxial grains were found by optical microscopy. In corrosion examination, the specimens of rolling and ECAE (Route A) developed exfoliation corrosions and the samples of ECAE (Route Bc) didn’t sustain exfoliation corrosion. This results were consistent with our previous report. Then the corrosion behavior of rolled and ECAEed samples were focused. The evaluation of the time until crack initiation and the number of cracks were employed to see the corrosion morphology of the samples

Role of subgrain stripe on the exfoliation corrosion of Al-4.6Mg-3.1Zn (wt.%) alloy

The role of subgrain stripe on the exfoliation corrosion behaviour in the Al-4.6 wt%Mg-3.1 wt%Zn alloy is revealed. The slight difference in the Volta potential distribution between the subgrain stripes and normal grains indicates that the selective corrosion in the subgrain stripes is not relevant to the electrochemical factor. Furthermore, the difference in the microstress state between two sides of the subgrain stripe boundary indicates a stress mechanism cooperate with the anodic dissolution mechanism is worked during the expansion of the selective exfoliation corrosion.

Electrochemical and Exfoliation Corrosion Behavior of Reversion-Treated High-Strength Aluminum Alloy

The present study aims to understand the microstructural modification affecting the electrochemical and exfoliation corrosion (EXCO) characteristics of aluminum alloy 7010. The alloy was aged for two different tempers, namely peak aging (T6) and retrogression and re-aging (RRA). The standard electrochemical polarization tests and EXCO tests were performed on the treated alloys. The microstructure of the alloy observed under a scanning transmission electron microscope revealed the presence of continuous grain boundary precipitates in T6 alloy. These precipitates were formed discontinuously after RRA treatment. The RRA alloy microstructure resulted in a shift toward positive potential. The exfoliation corrosion depth was reduced to 60–70 μm after RRA treatment, which was measured to be about 250 μm in T6 condition. The resistance toward the exfoliation corrosion was found to be influenced by the enriched Cu content of precipitates on grain boundary after reversion treatment. The results confirm that the RRA-tempered alloy improves both electrochemical corrosion and EXCO resistance.

Effects of aging treatment and peripheral coarse grain on the exfoliation corrosion behaviour of 2024 aluminium alloy using SR-CT

The exfoliation corrosion behaviour of 2024 aluminium alloy was investigated through exfoliation corrosion test, together with synchrotron radiation X-ray computed tomography (SR-CT) to achieve the 3D segmentation of precipitated phases, cracks and corrosion products. The results demonstrate that aging treatment has a significant effect on the distribution of the precipitated phases in the 2024-T4 aluminium alloy, and the precipitated phases continuously distributed along the grain boundary would lead to intergranular corrosion (IGC) which is easily evolved into exfoliation corrosion. In the 2024-T2 aluminium alloy, the longest crack was found to locate at the boundary between the inner grains structure and outer peripheral coarse grain (PCG) structure, which indicates that the corrosion is attributed to electrochemical property difference of two structures.

Effect of Pre-Aging, Over-Aging and Re-Aging on Exfoliation Corrosion and Electrochemical Corrosion Behavior of Al-Zn-Mg-Cu Alloys

By means of TEM, hardness, conductivity, tensile strength test, fracture toughness test, polarization curve and EIS, the Al-Zn-Mg-Cu alloys treated by a new multi-stage aging system, i.e. pre-aging, over-aging and re-aging (120°C/24h + 160°C/8h + 120°C/24h), were characterized. It is found that compared with the Al-Zn-Mg-Cu alloys treated by T76 (120°C/24h + 160°C/8h), the new multi-stage aging treatment can improve the tensile strength, fracture toughness, hardness and conductivity of the alloys at the same time. This is mainly due to the pre-aging, over-aging and re-aging process of super high strength aluminum alloys. Compared with the two-stage over aging process, the formation of multi-stage multi-phase precipitation structure can improve the strength, toughness and corrosion resistance of the alloys at the same time. The polarization curve is consistent with the conclusion. Therefore, we conducted this study to test how the comprehensive properties of the alloy can be improved.

Effect of Cu on the Fracture and Exfoliation Corrosion Behavior of Al-Zn-Mg-xCu Alloy

In the present work, the influence of Cu content on microstructure, mechanical properties and exfoliation corrosion behaviors of Al-Zn-Mg-xCu alloy extrusions has been investigated in longitudinal-transverse (L-T) and short-longitudinal (S-L) directions by means of mechanical tensile and exfoliation corrosion testing combined with optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that a higher Cu content significantly decreased the fracture toughness and ductility of the alloy in S-L direction compared with L-T direction. Concomitant with the increase in Cu content, a transition in fracture mode was observed from transgranular dimpled rupture to intergranular rupture in S-L direction. Moreover, the exfoliation corrosion (EXCO) resistance of the alloy decreased as the Cu content increased and the exfoliation corrosion resistance of the alloy in short-transverse (S-T) direction was better than that of L-T direction. These results were mainly associated with the large number of coarse intermetallics caused by high Cu content in the L-T direction of alloy.

Exfoliation Corrosion Behavior of 2A02 Al-alloy in a Simulated Marine Atmospheric Environment

Exfoliation Corrosion Behavior of 2A02 Al-alloy in a Simulated Marine Atmospheric Environment

ENHANCEMENT OF EXFOLIATION CORROSION RESISTANCE OF ALUMINIUM ALLOY 5083 BY SHOT PEENING

The present work is an effort to study the influence of shot peening on the exfoliation corrosion behavior of aluminium alloy (AA) 5083. Surface textural changes induced by shot peening was characterized using microstructural and X-ray diffraction analysis. The surface roughness parameters were measured to study the benefits of peening induced surface topography. Further, the hardness survey was carried out to assess the severe plastic deformation on the peened layers. As a result, excellent resistance against exfoliation corrosion was achieved in the chloride environment. Shot peening plays major role in enhancing the corrosion resistance of AA 5083. In the absence of exfoliation attack, the unpeened sample surfaces such as ground, milled, and as received conditions end up with a significant pitting attack. The findings of this work will be useful for the aluminium alloy fabrications involved in the marine applications.

Effects of aging mechanisms on the exfoliation corrosion behavior of a spray deposited Al–Zn–Mg–Cu–Zr aluminum alloy

Abstract

Effect of flame rectification on corrosion property of Al–Zn–Mg alloy

The corrosion resistance of Al–Zn–Mg alloy subjected to different times in flame rectification was investigated based on the exfoliation corrosion test. The results indicate that the flame rectification deteriorates the exfoliation corrosion resistance of Al–Zn–Mg alloy. The corrosion resistance of Al–Zn–Mg alloy is ranked in the following order: base metal>two times>three times>one time of flame rectification. The exfoliation corrosion behavior was discussed based on the transformation of precipitates at grain boundaries and matrix. With increasing the number of times in flame rectification, the precipitate-free zones disappeared and the precipitates experienced dissolution and re-precipitation. The sample was seriously corroded after one time of flame rectification, because the precipitates at grain boundaries are more continuous than those in other samples.

Influence of Retrogression and Re-aging on the Exfoliation Corrosion Behavior of AA 7085 Sheets

Influence of Retrogression and Re-aging on the Exfoliation Corrosion Behavior of AA 7085 Sheets

Synergetic effects of Sc and Zr microalloying and heat treatment on mechanical properties and exfoliation corrosion behavior of Al-Mg-Mn alloys

Mechanical properties, exfoliation corrosion behavior and microstructure of Al-5.98Mg-0.47Mn and Al-6.01Mg-0.45Mn-0.25Sc-0.10Zr (wt%) alloy sheets under various homogenizing and annealing processes were investigated comparatively by tensile tests, electrochemical measurements, X-ray diffraction technique and microscopy methods. The as-cast alloys mainly consist of Fe and Mn enriched impurity phases, Mg and Mn enriched non-equilibrium aluminides and Mg3Al2 phases. During homogenization treatment, solvable intermetallics firstly precipitate and then dissolve into matrix. The optimized homogenization processes for removing micro-segregation and obtaining maximum precipitation strengthening of secondary Al3(Sc, Zr) particles are 440°C×8h and 300°C×8h, respectively. Sc and Zr additions can make the yield strength of Al-Mg-Mn alloy increase by 21MPa (6.9%), 120MPa (61.2%) and 127MPa (68.3%), when annealed at 270°C, 300°C and 330°C, respectively, indicating that Orowan precipitation strengthening caused by secondary Al3(Sc, Zr) nano-particles is much greater than grain boundary strengthening from primary Al3(Sc, Zr) micro-particles. Increasing homogenization and annealing degrees and adding Sc and Zr all can decrease corrosion current density and improve exfoliation corrosion resistance. The exfoliation corrosion behavior is dominant by anodic dissolution occurring at the interface between intermetallics and ɑ(Al) matrix. After homogenizing at 440°C for 8h and annealing at 300°C for 1h, yield strength, ultimate strength, elongation to failure and exfoliation corrosion rank are 196MPa, 360MPa, 20.2% and PA (slight pitting corrosion) in Al-Mg-Mn alloy, and reach to 316MPa, 440MPa, 17.0% and PA in Al-Mg-Mn-Sc-Zr alloy, respectively, revealing that high strength, high ductility and admirable corrosion resistance of Al-Mg-Mn alloys can be achieved by the synergetic effects of Sc and Zr microalloying and heat treatment.

Exfoliation Corrosion Behavior of 2B06 Aluminum Alloy in a Tropical Marine Atmosphere

In this study, corrosion behavior of 2B06 aluminum alloy was investigated after exposure to a tropical marine atmosphere for up to 4 years. After 6 months, the specimen showed exfoliation corrosion as well as rapid increase in thickness loss and corrosion rate. Exfoliation corrosion was found to initiate from hydrogen-assisted intergranular cracks and propagate extensively due to the wedge effect of the corrosion products. During the exposure test, corrosion on the groundward surface was considerably more severe than that on the skyward surface, which could be attributed to the different exposure conditions on the two surfaces.

Exfoliation corrosion behavior of 7050-T6 aluminum alloy treated with various quench transfer time

The exfoliation corrosion (EFC) behavior of 7050-T6 aluminum alloy treated with various quench transfer time after solution heat treatment was investigated by standard EFC immersion tests, strength loss measurements after EFC tests and electrochemical impedance spectroscope (EIS) technique. The results showed that EFC resistance of the alloy decreased with increasing quench transfer time. Backscattered electron scanning electron microscope (SEM) together with transmission electron microscope (TEM) observations revealed that the coverage ratio and microstructure of precipitates at grain boundary area are the most important factors which influence the EFC susceptibility of the alloy, while precipitate-free zone (PFZ) near grain boundary has no or only a minor effect on it. In addition, galvanostatic measurements of the alloy present a good correlation between EFC resistance and transients in potential. The cumulated number of transients in potential can be used to evaluate EFC resistance of the alloy.

318 Mg-Li合金冷間圧延板の剥離腐食挙動に及ぼす加工量の影響(OS-4 マグネシウム合金の変形とメカニクス(5))

318 Mg-Li合金冷間圧延板の剥離腐食挙動に及ぼす加工量の影響(OS-4 マグネシウム合金の変形とメカニクス(5))