Exfoliation Corrosion Test Research Articles

Effect of intermittent non-isothermal aging on the microstructure and properties of Al–Zn–Mg–Cu alloy

The proposition of an intermittent non-isothermal aging (IM-NIA) is an innovative approach to address the challenge of balancing the mechanical properties and corrosion resistance of Al–Zn–Mg–Cu alloys. The effects of IM-NIA on the hardness, corrosion resistance and microstructure morphology of Al–Zn–Mg–Cu alloys were investigated by hardness test, intergranular corrosion test (IGC), exfoliation corrosion test (EXCO), electrochemical corrosion test and combined with transmission electron microscopy (TEM) observation. The results showed that the hardness of the alloy was the highest at 186HV after intermittent post-tempering to 180 °C (IM-H180). The intergranular corrosion depth is the smallest, the corrosion rate is the slowest, and the exfoliation corrosion rating is EA. In addition, the alloy matrix precipitated phase has the smallest average diameter, the highest volume fraction, the strongest ability to repair the passivation film, and the strongest resistance to Cl− erosion; At the same time, the grain boundary precipitation phase is intermittent and multilinear parallel distribution, PFZ is the widest, hindering the anodic corrosion channel, slow corrosion progress and improve corrosion resistance.

The Effect of High-Temperature Deformation on the Mechanical Properties and Corrosion Resistance of the 2024 Aluminum Alloy Joint after Friction Stir Welding.

The 2024 aluminum alloy is one of the high-quality lightweight materials. Friction stir welding (FSW) has shown advantages in reducing welding defects and improving welding quality in 2024 aluminum alloys. Currently, the research regarding FSW joint corrosion performance is mainly about the joint without plastic deformation. However, FSW joints often need to be formed into complex shapes by plastic deformation. The influence of plastic deformation on the corrosion performance of FSW joints is the focus of scientific research. To address this problem, the effect of high-temperature deformation on the mechanical properties and corrosion behavior of 2024 aluminum alloy joints was researched. The exfoliation corrosion test, scanning electron microscopy, energy-dispersive spectroscopy, and transmission electron microscopy were employed to analyze the corrosion mechanism and microstructure. The results show that high-temperature deformation of the weld nugget zone greatly affects the mechanical properties and corrosion behavior of the FSW joint. Compared with the 0% deformation specimen, the hardness and tensile strength of the 20% deformation FSW joint increased by 32% and 21%, respectively. The FSW joint with 20% deformation shows the best mechanical properties and corrosion resistance. The number of precipitated S' phases of the FSW joint increases when the deformation increases to 20%, and the shape of the S' phase is a regular round particle shape. The dislocation density of the FSW joint increases continuously during deformation, which provides a favorable nucleation location for the S' phase.

Study on the quenching sensitivity of corrosion properties in 7199 aluminum alloy

This study used electrochemical corrosion, intergranular corrosion (IGC), and exfoliation corrosion tests, as well as microscopic observations of the microstructure and first-principles calculations, to investigate the effect of different quenching rates on the microstructure and corrosion properties of the 7199 alloy. The results show that as the quenching rate decreases, the size, Zn, and Mg content of precipitated phases at grain boundaries (GBs), as well as the width of the precipitation-free zone (PFZ), increase, resulting in a decrease in corrosion properties. During slow quenching, the η phase (MgZn2) at the GBs continuously absorbs surrounding Zn and Mg atoms, causing Zn and Mg atom depletion near the GBs. This results in the formation of a wide PFZ. Enlargement of the η phase and PFZ at the GBs leads to anodic dissolution channels, allowing for rapid corrosion expansion along the GBs. Additionally, at slow quenching rates, not only does the η phase precipitate at the subgrain boundaries (SGBs) but also the T and S phases. In corrosive environments, the η phase is more prone to corrosion than the T and S phases. Electron work function calculations show that the S phase has the highest corrosion potential, whereas the η phase has the lowest. As a result, SGBs containing T and S phases are unlikely to serve as corrosion pathways. Corrosion preferentially extends along SGBs containing η phases.

Investigation on mechanical properties and corrosion behavior of dissimilar joints of 5083 and 6005A alloy welded by friction stir welding

AbstractIn this paper, the microstructure, mechanical properties, and corrosion behavior of friction stir welded (FSW) joints of the two aluminum alloys 6005A‐5083 were investigated and their correlation was discussed. In contrast to FSW joints of the same aluminum material, this results in a “V” shape curve of hardness distributed nonsymmetrically along the weld. The lowest hardness area occurs at the interface between the heat‐affected zone and the thermo‐mechanically affected zone of 6005A (6‐HAZ and 6‐TMAZ) due to the transformation of the β" phase under the influence of heat input during the stir friction process. This also leads to all tensile specimens fracturing in this area. The corrosion behavior of the FSW joint in acidic solution containing Cl− was determined by an exfoliation corrosion (EXCO) test, an intergranular corrosion (IGC) test, and potentiodynamic polarization measurements, based on the potential application in acid rain environment. The results showed that the corrosion resistance order in the acidic solution is: 6‐HAZ > NZ > 6‐BM > 5‐HAZ > 5‐BM. The 5‐BM has the worst corrosion resistance due to the high corrosion sensitivity of Al3Mg2 in acidic solution. However, good corrosion resistances are shown in NZ and 6‐HAZ, which is related to a relatively homogeneous microstructure in NZ and a dissolution or coarsening of β" phases in 6‐HAZ because of frictional heat input.

Effect of pre-aging process on microstructure and properties of 7075-T8 aluminium alloy

The 7075 aluminium alloy was treated by combining pre-aging and thermomechanical treatment to obtain excellent comprehensive properties. The properties of the alloy were investigated by hardness, exfoliation corrosion, intergranular corrosion, and electrochemical corrosion test. The microstructure of the alloy was observed by transmission electron microscopy. Furthermore, the relationship between microstructure evolution and performance change was investigated. The results showed that the hardness and corrosion resistance of the alloy were improved after the combination of pre-aging and thermomechanical treatment. With the change in the pre-aging temperature, the microstructure of the alloy changed significantly. The matrix precipitates were numerous, fine, and uniformly distributed, which significantly improved the hardness of the alloy, resulting in a peak hardness of 195.2 HV. The grain boundary precipitates were rounded and independent, the distance between the precipitates became large, and the discontinuous distribution was very obvious, which destroyed the formation of corrosion channels, hindered the development of corrosion, and effectively improved the corrosion resistance of the alloy. The exfoliation corrosion rating was P. The minimum depth of intergranular corrosion was 29.3 µm. The self-corrosion current density and corrosion rate were the lowest, 0.0013 mA/cm2 and 0.0427 mm/a, respectively.

Effect of deformation amount on microstructure and properties of AA2024-T8I4 with deep cryogenic treatment

To simultaneously improve the mechanical properties and corrosion resistance of AA2024 aluminum alloy, a T8I4 with deep cryogenic treatment (DCT) process is proposed, which includes solution heat-treatment, cold-drawing deformation, pre-aging, DCT and re-aging. The microstructure of AA2024 is observed by confocal laser scanning microscope, scanning electron microscopy and transmission electron microscopy. The properties of AA2024 are studied by hardness measurement, tensile test, friction and wear test, exfoliation corrosion test, intergranular corrosion test and electrochemical corrosion test. On comparison with T6, AA2024-T8I4 +DCT obviously increases its hardness, tensile strength and wear resistance. AA2024-T8I4 +DCT has similar corrosion resistance to T7X two-stage aging. According to comprehensive analysis, the MPts in AA2024-T8I4 +DCT with 3 % deformation amount have the maximum pinning force to the dislocations, and the alloy has the largest hardness, strength and the best wear resistance. The discontinuous grain boundary precipitates in AA2024-T8I4 +DCT with 1 % deformation amount are discontinuous and fine, and the precipitate free zone is not obvious, which makes the corrosion difficult to develop. The alloy has the shallowest intergranular corrosion depth, the smallest corrosion rate and the best corrosion resistance

Effect of secondary aging on microstructure and properties of cast Al-Cu-Mg alloy

To obtain better comprehensive properties of cast Al-Cu-Mg alloys, the secondary aging (T6I6) process (including initial aging, interrupted aging and re-aging stages) was optimized by an orthogonal method. The microstructures of the optimized Al-Cu-Mg alloy were observed by means of scanning electron microscopy and transmission electron microscopy, and the properties were investigated by hardness measurements, tensile tests, exfoliation corrosion tests, and intergranular corrosion tests. Results show that the S phase and θ′ phase simultaneously exist in the T6I6 treated alloy. Appropriately increasing the temperature of the interrupted aging in the T6I6 process can improve the mechanical properties and corrosion resistance of Al-Cu-Mg alloy. The optimal comprehensive properties (tensile strength of 443.6 MPa, hardness of 161.6 HV) of the alloy are obtained by initial aging at 180 °C for 2 h, interrupted aging at 90 °C for 30 min, and re-aging at 170 °C for 4 h.

Microstructure characteristics and corrosion behavior of refill friction stir spot welded 7050 aluminum alloy

Refill friction stir spot welding (RFSSW) of high strength aluminum alloy has a wide application prospect. However, there are few studies between the microstructure and macroscopic corrosion behavior, causing a significant impediment in corrosion protection of the joint. Therefore, the microstructure and corrosion behavior of 7050 aluminum alloy RFSSW joint was investigated in this paper. Due to the difference of microstructure, the joint can be divided into five zones, namely stir zone (SZ), thermo-mechanically affected zone (TMAZ), heat affected zone-I (HAZ-I), heat affected zone-II (HAZ-II) and base metal (BM). Therein, the grain size and the micron-sized second phase particles of SZ were fine, while other areas were coarse. And they were mainly Al2CuMg and Al7Cu2Fe. After intergranular corrosion and exfoliation corrosion tests, it was indicated that the grain morphology and second phase particles did not significantly affect the corrosion susceptibility, but the continuous degree of intergranular nano-precipitates was the key factor. A coefficient r was defined to quantitatively characterize the continuous degree of intergranular nano-precipitates. The HAZ-II and TMAZ exhibited high corrosion sensitivity with a high value of r, while HAZ-I and SZ exhibited low corrosion sensitivity with a low r. The corrosion mechanism was also briefly discussed.

Effects of a short-duration preprecipitation process prior to predeformation aging on the mechanical properties and corrosion resistance of Al-Cu-Mg-Ag alloy

PurposeThe effects of the thermo-mechanical treatment on the properties and microstructure of the Al–Cu–Mg–Ag alloy were investigated.Design/methodology/approachA short-duration preprecipitation process is designed prior to predeformation aging. The novel predeformation aging (solution treatment + holding at 185 °C for 15 min+ rolling deformation + aging at 185 °C, also named T8) was performed on a heat-resistant Al–Cu–Mg–Ag alloy.FindingsThe purpose of this study indicate that a short-duration heat treatment before predeformation is beneficial to the precipitation of O during the aging process. The precursors of O during this process might pin the dislocation and cause the grains to orient along some specific direction, which might be advantageous to the precipitation of O while disadvantageous to that of θ′. This novel thermal-mechanical process could result in an increase in the quantity and decrease in the size of the precipitation of O, which leads to a remarkable strength effect. The potential increases while the current density decreases with an increase in the deformation amount, which implies a smaller intergranular corrosion rate. The fine deformed structure leads to an opposite behavior in the exfoliation corrosion test compared with that for intergranular corrosion.Originality/valueThe intergranular corrosion resistance of the Al–Cu–Mg–Ag alloy is enhanced, whereas the exfoliation corrosion resistance is reduced by novel predeformation aging.

Effect of Deformation on the Corrosion Behavior of Friction Stir Welded Joints of 2024 Aluminum Alloy.

Friction stir welding (FSW) of aluminum alloys is an advanced manufacturing technology to realize lightweight bodywork. However, most studies only focus on the mechanical properties and corrosion behaviors of the welded joints. The effect of deformation on the corrosion behavior of FSWed joints is unclear. In this work, the plastic deformation behavior was characterized using uniaxial tensile tests. The effect of deformation on the corrosion behavior of a 2024 aluminum alloy nugget was studied by using a Tafel polarization curve, electrochemical impedance spectroscopy, exfoliation corrosion test, scanning electron microscopy and energy dispersive spectrometer, and transmission electron microscopy. The results show that the corrosion resistance of FSWed joints with different deformation degrees can be ranked as: 0% > 7% > 10% > 4%, and an “inflection point” appears at 7%. The corrosion potential and current density at 7% are near the values at 0%, and the 7% sample shows less corrosion rate than all other deformation samples. Only pitting and bubbling occur in the sample in 96 h. With an increase in plastic deformation, the dislocations and dislocation rings increase, there is an increase in the surrounding winding precipitates. The impurity phase is cleaved by dislocations; a reduction in the size of the impurity phase with low chemical activity can be observed, resulting in an increase in corrosion resistance. However, the transgranular and intergranular cracks appear on the 10% deformation sample. They almost always develop along the grain boundaries after initiation, making them more susceptible to corrosion.

Effect of Solid Solution Treatment on Corrosion Resistance of Al-Cu-Mg-Ag Alloy

In this experiment, Al-Cu-Mg-Ag alloy was used as material and solution temperature was used as variable to investigate its effect on the corrosion properties of the alloy and Hardness test, metallographic observation, electrochemical test, intergranular corrosion and exfoliation corrosion test were carried out on three groups of samples. The results show that the intergranular corrosion resistance of the alloy decreases with the increase of solution treatment temperature, and the sample treated at 505 °C has the best performance. This is mainly because grain boundary structure plays a role in increasing PFZ and expanding corrosion channels. The exfoliation corrosion resistance of Al-Cu-Mg-Ag alloy increases first and then decreases, and the sample treated at 515 °C has the best performance. This is due to the dual effects of grain boundary structure and grain morphology. On the one hand, the solution treatment temperature increases, which widens the precipitation-free zone and reduces the electrochemical corrosion resistance of the alloy. On the other hand, the increase of recrystallized grains decreases the cohesion of corrosion products and enhances the electrochemical corrosion resistance of the alloy.

Research on the corrosion behavior of double-side friction stir welded 6082Al alloy thick plate

In order to study the influences of microstructures on corrosion behavior of double-side friction stir welded 6082Al thick plate. The corrosion behavior was firstly clarified by potentiodynamic polarization and exfoliation corrosion (EXCO) tests. The microstructures before and after corrosion were identified by optical microscopy (OM), SEM and transmission electron microscope (TEM). The results showed that the corrosion resistance of heat-affected zone (HAZ) and base material (BM) was lower than those of thermo mechanically affected zone (TMAZ), top of NZ and middle of NZ. Bottom part of NZ was the most severe corroded zone. Intergranular corrosion along grain boundaries was the dominant corrosion type in BM, HAZ, TMAZ and bottom of NZ, while the top and middle part of NZ were susceptibility to pitting. The corrosion resistance decreased with the increase of weld pass. The precipitates mainly precipitated in NZ of the first pass and HAZ of both two passes during double side friction stir welding (FSW) due to the over aging process, which deteriorated the corrosion resistance.

Effect of heating rate during solution treatment on microstructure, mechanical property and corrosion resistance of high-strength AA 7075 alloy

The heating rate during solution treatment exerted great influence on the final grain structure of AA 7075 alloy processed by thermo-mechanical treatment (TMT). In case of rapid heating rate, particle-stimulated nucleation (PSN) of recrystallization occurred and fine equi-axed structure with an average grain size of ~9 μm was obtained. On the contrary, when a slow heating rate was adopted, the resulting recrystallized grains were rather coarse and elongated (average grain length > 100 μm). After peak-ageing treatment, the mechanical property and corrosion resistance of 7075 sheets were closely associated with those grain structures. Specifically, two kinds of sheets exhibited equivalent strength while the ductility of fine-grained sample is considerably increased to 18.5%, 49% higher than that (12.4%) of coarse-grained sheet. Meanwhile, inter-granular corrosion (IGC) and exfoliation corrosion (EXCO) tests certify that the fine-grained sheet exhibited significantly enhanced corrosion resistance. Effective grain refinement induced by rapid solution treatment accounts for the notable increment in both ductility and corrosion resistance. Our results demonstrate that the comprehensive properties of 7000 alloys might be tailored by adopting proper heating rate when the alloys are subjected to solution treatment.

Influence of aging treatments on the strength and localized corrosion resistance of aged Al–Zn–Mg–Cu alloy

The effect of multi-stage aging heat treatments on the hardness, tensile strength, electrical conductance, and exfoliation corrosion (EXCO) resistance of the Al–Zn–Mg–Cu alloy has been studied through the Vickers hardness, tensile, conductivity, and EXCO testing combined with microstructure characterization using a transmission electron microscope. Experimental results demonstrated that multi-stage aging conditions could effectively enhance the localized corrosion resistance through a lower strength loss compared to T6 aging condition (120 °C/24 h). The designed four-step aging (FSA) treatments could improve the EXCO properties to PB degree along with the ultimate tensile strength and yield strength to 373 MPa and 324 MPa, respectively. The development trend of localized corrosion resistances has been further verified using electrochemical impedance spectroscopy and polarization dynamic curves. Microstructures results indicated that dense precipitates in matrix, discontinuous coarse precipitates on grain boundaries, and a proper precipitation free zone play an important role in balancing the strength and corrosion properties of the FSA aged alloy.

Mechanical behavior associated with metallurgical aspects of friction stir welded Al–Li alloy exposed to exfoliation corrosion test

This research aims to investigate the effect of the exfoliation corrosion exposure time on the mechanical properties, the strength and elongation, of friction stir welded Al–Li alloy type 2195-T8. The exfoliation corrosion test was performed using the exfoliation corrosion (EXCO) solution, based on ASTM G34. The samples were exposed to different exposure times 24, 48, 96, 192 and 384 h. The results showed that both the strength and elongation of the welded specimens—exposed to the exfoliation corrosion tests—were reduced. For example, the samples that were exposed to 384 h, their initial tensile strength and elongation were reduced by 13% and 17% respectively. The degradation process due to the exfoliation corrosion on the tensile strength was divided into three stages: fast (0–96 h: 443.7 MPa-416.3 MPa, the degraded rate was 0.29 MPa/h), steady (96–192 h: 416.3 MPa-413.4 MPa, the degraded rate was 0.03 MPa h−1) and medium rate (192–384 h: 413.4 MPa-386.7 MPa, the degraded rate was 0.14 MPa h−1). For the elongation, in general, the reduction was similar to the style of strength, but with different rates. The TEM images showed that this degradation was due to the dissolution of T1 (Al2CuLi) and S′ (Al2CuMg) phase. Also, the corrosion products and their role of adherence on the surface of the tested specimens were investigated. An empirical equation p-t (mechanical properties-exposure time) was established to calculate the effect of exposure corrosion time on the performance of welded specimens.

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.

Effect of Mg Content on the Microstructure and Corrosion Properties of Al-Cu-Mn Alloy

In this paper, the effect of Mg content on the microstructure and properties of Al-Cu-Mn alloy was investigated. The microstructures and the mechanical properties of the alloys were studied by scanning electron microscopy and transmission electron microscopy, and Vickers hardness measurement, respectively. Furthermore, the effect of Mg content on the corrosion resistance of the alloys was explored by exfoliation corrosion test, intergranular corrosion test, and electrochemical techniques. The results show that the overall properties of Al-Cu-Mn alloy with 0.1 wt.% Mg are superior to other alloys. Specifically, the Vickers hardness of this alloy reaches 111.45 HV. The grating of exfoliation corrosion is EA, and the intergranular corrosion depth is 30.2 μm. It is believed that the improved mechanical properties and corrosion resistance of the Al-Cu-Mn alloy with 0.1 wt.% Mg result from the S phase formed in the alloy and the highly dispersive distribution of the θ phase.

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.

The influence of stabilization treatment on long-term corrosion resistance and microstructure in Er and Zr containing 5083 aluminum alloy

The effect of stabilization annealing on the long-term corrosion resistance and microstructure in Er and Zr contained 5083 aluminum alloy was studied using the nitric acid mass loss test (NAMLT), exfoliation corrosion (EC) test, accelerated sensitization annealing (ASA) at 175 °C and transmission electronic microscopy (TEM) observation. The results showed that the alloy in cold rolling state sensitized severely after the ASA. The long-term IGC and EC resistances improved significantly through stabilization treatment at 220 °C. The longer stabilization time, the better long term corrosion resistance. The precipitation evolution of the alloy during the ASA in cold rolling state and stabilization state were analyzed by TEM. The results showed that the β precipitates were not found at cold rolling state, but formed continuously along grain boundary during ASA at 175 °C for 2 h. After 12 h stabilization treatment from the cold rolling sample, β precipitates were isolated at the triple junctions and Al6(Mn,Fe) phase boundaries. During the further ASA at 175 °C for 2 h, β phases formed sparsely and separately at grain boundaries. The addition of stabilization treatment led to the morphology change of β phases during ASA, resulting in the improvement of long-term IGC resistance. Its mechanism was discussed thermodynamically and kinetically.

Microstructure and Corrosion Behavior of Friction Stir Welded Al Alloy Coated by In Situ Shot-Peening-Assisted Cold Spray

To improve the corrosion resistance of friction stir welded (FSW) joints, in situ shot-peening-assisted cold spray coating was applied to the surface of FSW joints. The microstructure and corrosion behavior of the coatings were investigated. The results showed that a dense coating was obtained by cold spraying technology. Moreover, the use of in situ shot-peening-assisted technology significantly reduced the porosity of the coating, which has a positive impact on the microstructure and the mechanical performance. Exfoliation corrosion tests showed that the coating affected positively on the corrosion resistance. On the coated surface, the craters caused by shot-peening particles were corroded in the form of exfoliation corrosion, while the exposed particles were corroded in the form of intercrystalline corrosion. This work provides a new approach to the corrosion protection of FSW joints.