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Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The mechanical and corrosion characteristics of the friction stir welds (FSW) are defined by the heat generated throughout the process. The backing plate material is crucial for effective temperature control during the FSW process. The detailed examination comprehends how the backing plate material influences the mechanical and corrosion characteristics of AA6061 FSW joints. In this investigation, FSW process variables such as backing plate, the rotation speed of the tool, and traverse speed were varied to obtain a suitable combination of parameters to achieve high corrosion resistance of joints along with satisfactory mechanical properties. An exfoliation corrosion test is carried out to determine the welds' corrosion resistance. An electrical conductivity test was performed to identify the relationship between hardness and electrical conductivity. The results demonstrated that the lowest corrosion rate, 0.8174 mm per year (mm/year), was achieved by a weld produced using an aluminum backing plate at 1200 rpm and 60 mm/min. The weld with the composite backing plate at 1200 rpm, 30 mm/min exhibits the highest corrosion rate of 1.559 mm/year. The maximum ultimate tensile strength (UTS) is found in joints with an aluminum backing plate. Visual observations indicate that post-weld machining improves the corrosion resistance of FSW samples. [ABSTRACT FROM AUTHOR]

A high-strength and anti-intergranular corrosion (IGC) Al-6.8Zn-2.2 Mg-Sc-Zr alloy (AS alloy) was designed, and the effects of Sc addition and Cu removal on the microstructure, mechanical properties and corrosion behavior were systematically investigated. Based on transmission electron microscopy (TEM) and Kelvin probe force microscopy (KPFM) techniques, the underlying causes of IGC and exfoliation corrosion (EXCO) of the AS alloy were investigated, and the corrosion mechanism of AS alloy was finally obtained. The AS alloy exhibits excellent mechanical properties with a tensile strength of 601 MPa in the peak-ageing condition at 120 °C, which comes from the pinning effect of Al3(Sc, Zr) dispersions. Moreover, AS alloys of T6 and T74 conditions show outstanding IGC and EXCO resistance. On the one hand, the fine, near-ellipsoidal grains in AS alloy alleviate the peeling stress caused by IGC products by blocking the formation of wedge-shaped gaps along GBs, which then bring about improved EXCO resistance. On the other hand, the removal of Cu from the traditional Al-Zn-Mg-Cu alloy avoids the segregation of Cu into GBs and thereafter reduces the fluctuations of the potential and the electron work function (EWF) across the GBs; the addition of Sc induces the high fraction of LAGBs and thus weakens the solutes' segregation at GBs, which can be beneficial for smoothing the fluctuation of corrosion potential (Ecorr) to enhance the IGC resistance.

The influence of grain structure and quenching rates on the exfoliation corrosion (EXCO) susceptibility of 7085 alloy was studied using immersion tests, optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and scanning transmission electron microscopy (STEM). The results show that as the cooling rate decreases from 1048 °C/min to 129 °C/min; the size of grain boundary precipitates (GBPs); the width of precipitate-free zones (PFZ); and the content of Zn, Mg, and Cu in GBPs rise, leading to an increase in EXCO depth and consequently higher EXCO susceptibility. Meanwhile, there is a linear relationship between the average corrosion depth and the logarithm of the cooling rate. Corrosion cracks initiate at the grain boundaries (GBs) and primarily propagate along the HAGBs. In the bar grain (BG) sample at lower cooling rates, crack propagation along the sub-grain boundaries (SGBs) was observed. Compared to equiaxed grain (EG) samples, the elongated grain samples exhibit larger GBPs, a wider PFZ, and minor compositional differences in the GBPs, resulting in higher EXCO susceptibility. [ABSTRACT FROM AUTHOR]

A recently developed AA7075 was subjected to solid solution, high temperature laser surface treatment and artificial aging. The microstructure evolution and precipitation behavior were examined, and their effects on corrosion behavior and corrosion cracking were analyzed. The results show that the coarse η phase disappears and many smaller η phases are formed after high temperature laser surface treatment. Most of the phases dissolved into Al matrix during solution, and fine η phases precipitated in laser treatment. The η′ phases were appeared in the high temperature laser surface treatment samples. It was concluded that reasonable laser scanning power owned the best corrosion resistance, lower intergranular corrosion tendency. Both lower laser scan power and higher scan power samples were susceptible to the intergranular corrosion, and the intergranular cracking was observed. In contrary, the reasonable sample which the laser power is 1000 W showed much better corrosion resistance due to the coarsening and separation of grain boundary precipitations. [ABSTRACT FROM AUTHOR]

Temperature has an important impact on the corrosion resistance of mold with cooling channels prepared by casting method. The effect of preheating temperature of the mold and the carbon fiber core on the roughness and corrosion resistance of U-shaped cooling channels made of Al-12Si alloy was examined in depth. The experimental results suggest that as the preheating temperature increased from 273 K to 573 K, the roughness of the inner wall of the cooling channel reduced from 96.6 µm to 77.0 µm. When the preheating temperature continued to increase to 723 K, the roughness increased to 85.3 µm. The wetting between the Al melt and the carbon fiber will reduce micro bubbles and waves on the channel wall as the preheating temperature rises, thereby reducing the roughness. However, with the further increase of preheating temperature, it will increase the solidification time of the Al melt. At this time, the carbon fiber and Al melt will take more time to react, which increases the roughness of the channel wall to a certain extent. The results of exfoliation corrosion show that the larger roughness will aggravate exfoliation corrosion. The prolongation of high temperature reaction time between the carbon fiber and the Al melt will lead to the segregation of Si, which is easy to cause intergranular corrosion. Therefore, reasonable preheating temperature has an important impact on the roughness and corrosion resistance of U-shaped cooling channels. [ABSTRACT FROM AUTHOR]

The third-generation alloy, AA2198-T8, is highly recommended for the aerospace industry. However, it has come under scrutiny due to its high cost. This study aims to decrease the cost of manufacturing through a hybrid design that uses AA2198-T8 alloys for the crucial parts and AA2024-T3 alloys for the remaining structure. The two main techniques for joining AA2024-T3 to AA2198-T8 are reversed double-sided friction stir welding (DS-FSW) and traditional single-sided friction welding (SS-FSW). They were carried out under unaltered tool rotation speed followed by five different welding speeds. The mechanical properties of the joints were explored, and the maximum joining efficiency of the welding process was 96% for reversed DS-FSW at 102 mm/min welding speed. The hybrid joint was tested for compliance with ASTM G34 standards to examine the welding joint's exfoliation corrosion (EXCO) for eight exposure times. The findings showed that joint efficiency decreased relative to as-welded joints, and mechanical property deterioration increased with EXCO exposure duration, reaching 40% for specimens exposed for 120 h to the corroding solution. It has been noted that morphology and grain size changes significantly impact EXCO.

The purpose of this paper is to highlight the evolution and corrosion damage that can occur in alloy 7175 after exposure to an aggressive corrosion solution. Susceptibility of 7xxx series aluminum alloys to exfoliation corrosion can be evaluated by the corrosion exposure test known as the EXCO test, which consists of accelerated exposure in a chloride solution and comparison of the corroded surface with standard micrographs. [ABSTRACT FROM AUTHOR]

Continuous retrogression and re-ageing (CRRA) treatment is designed to achieve an optimal balance between the strength and corrosion performance of an Al-Zn-Mg-Cu alloy. The findings suggest that intergranular corrosion predominantly affects the T6 sample, with extensive propagation into the bulk resulting in delamination and intergranular cracking. In contrast, crystallographic pitting dominates in the CRRA-treated sample, which effectively mitigates exfoliation corrosion and suppresses intergranular cracking. The different corrosion resistance between the T6 sample and the CRRA-treated sample is attributed to the disparate distribution of Cu in the alloy, which influences the corrosion rate, the types of corrosion and corrosion propagation path. [Display omitted] • Continuous retrogression and re-ageing treatment is designed for high strength and corrosion resistance of Al-Zn-Mg-Cu alloy. • Intergranular corrosion (IGC) prevails in T6 sample, whereas pitting is the predominant form in the CRRA-treated sample. • IGC can propagate deep into bulk to cause catastrophic peeling and facilitates the intergranular cracking. • Crystallographic pitting resulting from pitting restricts corrosion propagation and intergranular cracking. [ABSTRACT FROM AUTHOR]

The present study investigates the exfoliation corrosion (EXCO) mechanism of the surface layer (SL) and central layer (CL) of 2195 aluminum alloy extruded plates under different quenching rates. The results indicate that with a decreasing quenching rate, the EXCO resistance of both SL and CL samples improves, with the EXCO grades reducing from PB and EA to N and PB, respectively. This is contrary to the results of the EXCO quench sensitivity study in 7XXX series aluminum alloys. Furthermore, as the quenching rate decreases, the corrosion depth of SL samples decreases (from 138 to 79 μm) while that of CL samples increases (from 216 to 505 μm). Combined with microstructural characterization, the study elaborates in detail on the EXCO corrosion mechanism of the alloy's SL and CL, providing a theoretical basis for preparing aluminum-lithium alloys with higher corrosion resistance. [Display omitted] [ABSTRACT FROM AUTHOR]

Aluminum alloy BS.1476-HE.15 by virtue of its high strength and low density finds application in the form of bars or sections for cranes, bridges, and other such structures where a reduction in dead weight load and inertia stresses is advantageous. Bars and sections in H.15 alloy are mostly produced by extrusion. Some material processed this way has been prone to exfoliation corrosion. Extended aging for 24 h at a temperature of 185 °C (365 °F) virtually suppresses the tendency for exfoliation corrosion to develop. Also, the use of a sprayed coating, either of aluminum or Al-1Zn alloy, was effective in halting and preventing this form of attack. While alarming, the appearance of exfoliation corrosion provides a valuable warning to the engineer or inspector before a severe weakening of the particular sections has occurred. [ABSTRACT FROM AUTHOR]

The different effects of TiB 2 on intergranular corrosion (IGC) and exfoliation corrosion (EXCO) in TiB 2 /7075 composites were investigated. Lower particle content accelerated IGC due to the first dissolution of large TiB 2 /Al interface precipitates, causing TiB 2 deposition in corrosion channels. Conversely, higher particle content reduced the maximum IGC depth to 47 % with dense corrosion products inhibiting penetration of corrosive solution. EXCO weight loss increased by 271 % and 388 % with 3.5 wt% and 7 wt% particles, respectively. Micro-galvanic corrosion and recrystallization caused by particles reduced EXCO resistance. The passive IGC environment and active EXCO environment lead to different corrosion resistances of composites. • In IGC test, low-content TiB 2 increased corrosion susceptibility, while high-content TiB 2 enhanced corrosion resistance. • The dissolution of larger TiB 2 /Al interfacial precipitates resulted in TiB 2 deposition in corrosion channels during IGC. • In EXCO, corrosion resistance decreased with more micro-galvanic corrosion and recrystallized grains as TiB 2 increasing. • An in-situ observation was utilized to assess exfoliation corrosion (EXCO) susceptibility. [ABSTRACT FROM AUTHOR]

In order to study compatibility of tank materials and liquid propellants, electrochemical tests and full immersion tests were utilized to explore the corrosion mechanism of 2195-T8 aluminum lithium alloys in HNO3, and the corrosion process was simulated based on cellular automata method. The results show that the alloy has the fastest corrosion rate in HNOj whose mass fraction is as 30%; pitting corrosion occurs in the early stage of corrosion, and then gradually forms exfoliation corrosion. The fitted equivalent circuit reflects the dynamic processes of the alloys in HNO3 and explains the phenomenon of inductive reactance in the fourth quadrant of electrochemical impedance spectroscopy. Cellular automata model adopted Logistic distribution probability as critical condition of corrosion probability, and the simulation results correspond to that of the tests. [ABSTRACT FROM AUTHOR]

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 microstructure and corrosion behavior of a high‐strength Al–Zn–Mg–Cu–Mn alloy friction stir welded (FSWed) joint were investigated using scanning electron microscope, transmission electron microscope, open‐circuit potential test, and potentiodynamic polarization. The weld nugget zone and heat‐affected zone (HAZ) of the FSWed joint showed diverse microstructural characteristics including micron‐scale intermetallic particles and nanoscale precipitates, leading to different localized corrosion sensitivities. The results of electrochemical tests confirmed the regional difference of corrosion in FSWed joints. Detailed research on the corrosion process revealed that micron‐scale Al(Fe,Mn,Si) particles promoted the dissolution of the vicinal matrix to induce pitting corrosion. The directionally distributed intermetallic particles and grain boundary precipitates in HAZ conduced to the development of intergranular microcracks into exfoliation. The matrix precipitates affected the localized corrosion tendency due to regional variation of the redissolution degree. [ABSTRACT FROM AUTHOR]

In this study, the resistance to exfoliation and intergranular corrosion (IGC) of the 2198 Al–Cu–Li alloy submitted to different thermomechanical treatments (T3, T8, and T851) was investigated. The tests were carried out following the standard practices, ASTM G34‐18 and ASTM G110‐15, respectively. All the tested alloys showed susceptibility to exfoliation and some alloys showed susceptibility to IGC, but the artificially aged alloys presented a higher tendency to exfoliation. The extensive hydrogen evolution reaction (HER) was observed on the surfaces of artificially aged alloys when immersed in the EXCO solution. The HER resulted in an increase in solution pH with the time of immersion. Also, the weight losses related to the artificially aged alloys were higher than that of the naturally aged ones. The T8 treatment was the only condition that resulted in susceptibility to both, intergranular and transgranular corrosion, whereas the T851 treatment did not show IGC susceptibility, only transgranular corrosion. Finally, the 2198‐T3 condition showed the highest corrosion resistance among the thermomechanical treatments tested. The results of the 2198 alloy subjected to various treatments were compared with that of the 2024‐T3 alloy. This last alloy showed higher resistance to exfoliation and IGC as compared with the 2198 alloy. [ABSTRACT FROM AUTHOR]

5083 aluminum alloy with different compositions is designed by orthogonal design method. Research methods such as Intergranular corrosion,exfoliation corrosion,and polarization curve were used. The effects of Mn， Zn,Mg and Si on the corrosion resistance of 5083 aluminum alloy were characterized by metallographic microscope， scanning electron microscope，and energy dispersive spectrometer. And the optimun composition range of each element in 5083 aluminum alloy was obtained. The results show that the Mn content is about 0. 5%, the Si content is less than 0. 2% , t he Zn content is about 0. 14%，the Mg content is about 4. 3 %，and remain elements within the composition range , t he corrosion resistance of 5083 aluminum alloy is better [ABSTRACT FROM AUTHOR]

The tribological impact of the steel alloy employed as the work roll material during hot rolling on the surface quality and corrosion behavior of Al-Mn alloys was explored. AISI 52100, AISI D2 and AISI 440C steel work rolls with a surface roughness (Ra) of 0.1 µm were used to hot roll Al-Mn alloy specimens under similar conditions using a rolling tribo-simulator. Corrosion tests were then performed on the rolled Al-Mn specimens by immersing them in a 0.5 wt.% NaCl solution. Surface examination of the Al-Mn specimens after rolling revealed dark MgO-rich islands covering the surfaces of the AISI D2 and AISI 440C-rolled Al-Mn surfaces. These features were associated with the carbides observed protruding from the AISI D2 and AISI 440C steel surfaces. Subsequent corrosion tests revealed that these MgO-rich islands possessed a distinct influence on the corrosion behavior of the rolled Al-Mn surfaces. The frequency of occurrence and depth of the MgO-rich islands, which were dependent on the work roll material employed, influenced the initial and subsequent corrosion morphology detected on the Al-Mn surfaces. The preferential dissolution of the MgO-rich islands was detected as one of the corrosion mechanisms occurring during the early stages of corrosion. [ABSTRACT FROM AUTHOR]

In this paper, quantitative investigation of localized corrosion, in particular, exfoliating corrosion (EXCO) of aluminum alloys 2024 T3 and 7075 T6, is carried out. The mechanism of EXCO focusing on the effects of the combination of materials/environment/mechanical stress was also considered. An optical microscope (MO) and a scanning electron microscope coupled with a energy-dispersive spectroscope (EDX) were used to examine the microstructural stat. Tensile tests were conducted on plate specimens to discern the degradation of mechanical properties after the corrosion attack. Fatigue tests were conducted on compact tension specimens to correlate the influence of corrosion/microstructure coupling on the fatigue behavior of different aluminum alloys. The crack growth rate of the different materials for pre-corroded specimens was affected according to the microstructure of these two alloys. [ABSTRACT FROM AUTHOR]

The intergranular corrosion and exfoliation corrosion properties of 7475-T7351 aluminum alloy plate for aviation were investigated, and the corrosion behaviors of the alloy were analyzed by metallographic analysis(MA) and transmission electron microscope(TEM). The results show that no obvious intergranular corrosion is observed, but exfoliation corrosion grade of 7475-T7351 aluminum alloy increases from EA on surface to EC in the core. The exfoliation corrosion of 7475 alloy plate is mainly because of the typical lamellar structure, and the pathway formed by galvanic corrosion on grain boundary. The expansion of grain boundary corrosion product volume produces the wedging force,makes intergranular corrosion grow along the direction in parallel with the surface,and then gradually evolves into exfoliation corrosion. The degree of recrystallization decreases gradually from the surface to center, and the grain length-to-width radio increases, which inclines to exfoliation corrosion and leads to the exfoliation corrosion grade increasing from surface to center.

In this study, a retrogression process (R) has been applied to AA7075 at 180, 240, and 370°C for 15, 30, 90, and 120 min. After the retrogression, reaging treatment (RA) was reapplied with T6 conditions (120°C for 24 hr). The effect of different temperatures and time periods of retrogression and reaging temper on exfoliation corrosion (EXCO) of the AA7075 is examined. The EXCO solution was prepared in accordance with the ASTM G34‐01 standard and the samples were kept in the solution for 48 hr. Susceptibility of the alloy to EXCO was determined by weight loss detection, macro and microstructure studies, scanning electron microscope, transmission electron microscope, and energy dispersive X‐ray analyses. The mechanical properties of aged samples were determined by hardness, tensile tests, and fractography. [ABSTRACT FROM AUTHOR]

The effects of different retrogression times and temperatures on the microstructure, electrical conductivity, exfoliation corrosion (EXCO), and hardness of the 7050 aluminium alloy were compared with the T6 and T7451 condition. The EXCO solution was prepared in accordance with ASTM G34‐01 standard and the samples were kept in the solution for 48 hr. Corrosion depths were examined by using scanning electron microscope (SEM) in the cross‐sections microstructure of the samples. The effect of EXCO on the material was investigated using stereo optical microscope images. In microstructure investigations, SEM and energy dispersive X‐ray (EDX) analyses were used to determine the distribution and chemistry of the precipitates at the grain boundaries. The results show that retrogression and reaging (RRA) times and temperatures have significant effects on AA7050 EXCO. Especially after 200°C/30 min RRA process, it has been found that 7050 aluminium alloy has higher mechanical strength than T6 level and high corrosion resistance from T7451 level. According to the results of this study, it has been shown that there is a direct connection between electrical conductivity and EXCO. [ABSTRACT FROM AUTHOR]

The heat affected zone (HAZ) on the metal–inert gas (MIG) welding joint of 7N01 aluminium alloy was repaired by multipass narrow gap laser welding. The Y–X direction precracked three‐point bending sample was used in the alternate immersion test. The morphology of specimen surfaces demonstrated that the exfoliation corrosion in the HAZ after laser repair (HAZa) was more serious than that before laser repair (HAZb). The electrochemical impedance spectroscopy after different immersion corrosion time indicated that the HAZa and HAZb had similar corrosion potentials. However, the pitting corrosion resistance of HAZa was lower than that of HAZb at the beginning of exfoliation corrosion. The stress corrosion crack (SCC) of 7N01P‐T4 aluminium alloy displayed a multicrack source and an intergranular crack propagated along the rolling grain boundary under the test condition. An unusual method was taken to measure the length of SCC. The results showed that laser repairing did not weaken the stress corrosion resistance of the original joint. [ABSTRACT FROM AUTHOR]

In the present study, the microstructure and localized corrosion behavior of three Al-Zn-Mg-X alloys with Sc addition (MSc), Cu addition (MCu) and Cu + Sc addition (MCuSc) under T74 (121 °C/6 h + 163 °C/24 h) condition have been investigated. Electron backscattered diffraction and transmission electron microscope were used to analyze the microstructure of the three alloys. Pitting corrosion, intergranular corrosion, stress corrosion cracking, ASTM B117 salt spray exposure testing, and electrochemical tests, were carried out to investigate the corrosion behavior of the three alloys. Results show that the addition of Sc and/or the removal of Cu can greatly improve the localized corrosion resistance of the Al-Zn-Mg-X alloys. The pitting corrosion in the MCu and MCuSc alloys is severer than that in the MSc alloy, which is mainly attributed to the dealloying effect occurred in the Al 7 Cu 2 Fe and Al 2 CuMg instead of Al 3 (Sc x Zr 1-x) particles. The MSc alloy shows the highest resistance to pitting corrosion, EXCO and SCC. The modified GB features and the decreased potential difference between the GB precipitates and matrix were found to be the key factors to improve corrosion resistance of Al-Zn-Mg-X alloys. This provides a theoretical and experimental basis for the design of new Al-Zn-Mg-X alloys with excellent corrosion resistance and mechanical properties. • The Sc addition improves the localized corrosion resistance of Al-Zn-Mg-X alloys. • The removal of Cu can improve the resistance to SCC and EXCO of Al-Zn-Mg-X alloys. • Dealloying occurs in Al 7 Cu 2 Fe and Al 2 CuMg but not in Al 3 (Sc x Zr 1-x) particles. [ABSTRACT FROM AUTHOR]

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 T _1 (Al _2 CuLi) and S′ (Al _2 CuMg) 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.

Highlights • As-received and sensitized 5083-H116 behave similarly in high temperature creep. • All 5083-H116 damaged states failed alike at the extreme case of 400 °C and 18 MPa. • The Kachanov-Rabotnov model was applied to sensitized and corroded 5083-H116. • Adjusted for remaining section, corroded and uncorroded samples had akin lifetimes. Abstract Elevated temperature exposure of 5XXX alloys causes sensitization, which leads to changes in room temperature mechanical properties and may lead to intergranular corrosion (IGC) susceptibility. The influence of sensitization and corrosion damage on the creep response of 5083-H116 at various temperatures (representative of fire damage) from 200 °C to 400 °C has been examined in this experimental study. Sensitization had a negligible effect on creep properties, while corrosion damage led to a reduction in creep rupture time and steady state creep rates. After accounting for sensitization and corrosion damage, creep rupture can be predicted based upon secondary creep/steady state creep rates. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The effect of the retrogression and re‐aging (RRA) heat treatment on the corrosion behavior of B206 aluminum‐copper casting alloy in artificial seawater employing electrochemical experiments such as electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization, weight loss measurements and microstructure studies is reported. The electrochemical results show that the corrosion resistance of RRA samples is much higher than that of the as‐cast microstructure for the first 48 h of immersion in artificial seawater. However, the RRA samples corrode more rapidly after 48 h of immersion. Weight loss measurements confirm the electrochemical findings. The dependence of the corrosion rate on immersion time for RRA samples was found to be related to the microstructural features. Exfoliation corrosion was also observed in the cross‐section of RRA samples after 48 h of immersion in artificial seawater. [ABSTRACT FROM AUTHOR]

CNTs have been introduced into C/C composites by electrophoretic deposition to improve their ablation performance. Mass ablation of C/C composites decreases by 64% with an optimized CNT content. Mechanical exfoliation is mainly responsible for the mass loss of C/C composites under oxyacetylene ablation as confirmed by SEM observations and static oxidation experiments. By applying CNTs with an optimized content, thermal conductance of the composites increases by 24.5% and the fiber-matrix interfacial strength increases by 74.6%. Local thermal damage is significantly relieved and matrix peeling off by high-velocity gas is inhibited, which lead to the significant decrease of mechanical ablation. [ABSTRACT FROM AUTHOR]

In this work, the effect of microstructure on exfoliation corrosion (EXCO) resistance in an Al-Zn-Mg alloy were investigated using standard EXCO test, together with detailed microstructural examinations mainly by scanning electron microscopy (SEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). An EXCO product model was built based on morphologies of EXCO product on longitudinal section and cross section for further measurement and analysis. A quantitative characterization of EXCO resistance by measuring average thickness of EXCO product was conducted, showing average results of 6.94 μm, 10.21 μm and 18.14 μm, which are corresponding to EXCO ratings of P, EA and EB under ASTM G34 standard, respectively. It was concluded that recrystallization, high fraction of high-angle grain boundaries (HAGBs) and high coverage ratio of η phases on HAGBs reduced EXCO resistance. [ABSTRACT FROM AUTHOR]

AA7075 alloys susceptibility to exfoliation corrosion is related to distribution and size of precipitate within grain boundary, continuity within grain boundary and electrochemical behaviour. Distribution and size of precipitate in the grain also effects the conductivity of the material. The effect of different temperatures and time periods of RRA temper on exfoliation corrosion of AA7075 alloy is examined in this study. Exfoliation corrosion (EXCO) solution was prepared in accordance with ASTM G34-97 standard and the samples were kept in the solution for 48 h. After the samples were processed in the solution, the susceptibility of the alloy to exfoliation corrosion, its electrical conductivity and pH values of the solution were determined using microstructure scanning. It was determined that exfoliation corrosion resistance value and electrical conductivity changed in relation to chosen temperature and time of RRA temper. [ABSTRACT FROM AUTHOR]

The corrosion behavior of keyhole-free friction stir spot welded joints of dissimilar 6082 aluminum alloy and DP600 galvanized steel in 3.5% NaCl solution has been investigated by the immersion test and electrochemical analysis. The surface of the aluminum alloy produced exfoliation and pitting corrosion. The pitting occurred seriously on the interface of the 6082 aluminum alloy, but the steel had no corrosion. The corrosion galvanic couples were formed between elements of Si and Fe with a high electrode potential, and Mg and Al with a low electrode potential, around them. Mg and Al elements of Mg2Si and Si-containing solid-solution phase α (Al) preferentially became an anodic dissolution and formed exfoliation corrosion around the Si elements. Fe-rich phase θ (Al3Fe) as the cathode caused corrosion of Mg and formed pitting around Mg-rich phase β (Al3Mg2) as the anode. The sequence of the corrosion resistance of different areas of the joints (with decreasing corrosion resistance) was WNZ (Weld Nugget Zone) > TMAZ (Thermo-mechanically Affected Zone) > BM (Base Metal) > HAZ (Heat-affected Zone). The joints of keyhole-free FSSW (Fiction Stir Spot Welding) of dissimilar 6082 aluminum alloy and DP600 galvanized steel have better corrosion resistance than base metal in 3.5% NaCl solution. [ABSTRACT FROM AUTHOR]

The effect of rare earth metals on mechanical and corrosion properties of 7085 aluminum alloy (Al-7.5Zn-1.5Mg-1.4Cu-0.15Zr) was investigated by means of optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Intergranular, exfoliation corrosion, hardness, tensile test and electrical conductivity test were performed Al alloys on both with and without rare earth additives. Results show the Al alloys with rare earth metals present better mechanical properties such as higher strength and hardness as a result of finer microstructure in comparison with those without the additives. The corrosion resistance is greatly improved by adding rare earth metals. Intergranular corrosion resistance is enhanced from Level IV to Level II, the denudation level for 48 h is improved from E B to P A and I SSRT reflecting stress corrosion resistance was enhanced from 65% to 96%. [ABSTRACT FROM AUTHOR]

The exfoliation corrosion (EXCO) sensitivities and electrochemical corrosions of A7N01 aluminum (Al) alloys with 0.074% and 0.136% Cu contents were investigated in EXCO solution. The exfoliation corrosion developed more rapidly for the alloy with 0.136% Cu by expressing higher exfoliation rate and deeper corrosion pits as observed by SEM and laser confocal scanning microscopy (LCSM). In EXCO solution, the alloy with 0.136% Cu content showed lower open-circuit potential (OCP) than the alloy with 0.074% Cu content. The alloy with 0.136% Cu content had bigger 'hysteresis loop' in cyclic polarization curve which meant lower self-passivation ability. In electrochemical impedance spectroscopy plot, its curvature radius and capacitance index were lower. The electrochemical test results revealed that the alloy with 0.136% Cu content showed more severe electrochemical corrosion than the alloy with 0.074% Cu content, consistent with the exfoliation corrosion results. The microstructures of two alloys were observed through optical microscopy (OM) and transmission electron microscopy (TEM). The continuous distribution of the equilibrium precipitate -MgZn2 on grain boundaries, the decreasing of the width of precipitate-free zone (PFZ) and the coarse Cu-Fe-Si-rich phase were responsible for the higher corrosion sensitivity of the Al alloy with 0.136% Cu than that of Al alloy with 0.074% Cu content in EXCO solution. [ABSTRACT FROM AUTHOR]

The 7N01-T5 alloy (AT5) and 7N01-T4 alloy (AT4) were butt welded by metal inert gas (MIG) welding with ER5356 filler wire, and the mechanical properties and corrosion resistance of welded joint were investigated. The mechanical properties of welded joint are inferior to those of base metals (BMs). In the welded joint, the difference in composition of Zn, Cu and the amount of precipitates between AT5 side and AT4 side induces the variance of corrosion potential, resulting in the appearance of galvanic corrosion, then the highest corrosion susceptibility occurred on the AT4 side of the region adjacent to the weld zone. [ABSTRACT FROM AUTHOR]

An improved low-temperature thermo-mechanical treatment (LTMT based on DYA: dynamic aging) aiming to discover the action of deformation-induced precipitation to microstructures and corrosion resistance was proposed that included a conventional T6 peak aging (120 °C/24 h) and a subsequent dynamic aging. Its influence on mechanical properties, electrochemical behavior and intergranular/exfoliation corrosion resistance of 7055 Al alloy were investigated by tensile testing, polarization curve, intergranular/exfoliation corrosion testing combined with optical microscope and transmission electron microscope observation. It shows that after the conventional T6 peak aging, the matrix precipitates were fine and dispersive while the grain boundary precipitates were coarse and continuously distributed. With the introduction of dynamic aging, the grain boundary precipitates become discontinuously distributed gradually without much coarsening of matrix precipitates. As a result, the LTMT process can improve intergranular/exfoliation corrosion resistances without sacrificing strength that could be attributed to the discontinuous grain boundary precipitates and fine dispersed matrix precipitates, respectively. The improved corrosion resistance was also confirmed by polarization curves and conductivity test. It indicates that the present LTMT process may be a good alternative to produce heat-treatable Al alloy sheets with good strength and corrosion resistance. [ABSTRACT FROM AUTHOR]