Intergranular Corrosion Resistance Research Articles

Grain boundary structures and their correlation with intergranular corrosion in an extruded Al-Mg-Si-Cu alloy

A detailed analysis of grain boundaries in a highly textured Al-Mg-Si-Cu alloy is presented in this work. Electron backscatter diffraction demonstrates the presence of three main categories of grain boundaries in addition to sub-grain boundaries. These grain boundaries have been systematically analysed using high–resolution scanning transmission electron microscopy. Intergranular corrosion (IGC) susceptibility was statistically correlated with the same defined grain boundaries. A high density of metastable Q′-phase grain boundary particles correlates with a reduction in Cu segregation at grain boundaries and increased IGC resistance. Results herein are relevant in further understanding grain boundary structures in Al-Mg-Si-Cu alloys and their susceptibility to IGC, and can be implemented into modelling frameworks.

Mechanical Response of Ni-Based CU5MCuC Alloy to Different Stabilization Thermal Treatments

The Ni–Fe–Cr system is the basis of a series of commercial alloys featuring chemical–physical characteristics that allow them to be used in a variety of fields where excellent resistance to aggressive environments is required. In this scenario, the CU5MCuC alloy, the foundry counterpart of Alloy 825, is proving successful in the petrochemical field thanks to its good corrosion resistance in acidic and highly oxidizing environments. Intergranular corrosion resistance, critical for this material, is ensured by the stabilization treatment that allows precipitation of Nb carbides. Strengthening of this alloy takes place only via a solid solution. Therefore, its mechanical properties depend on the solution annealing treatment: often this treatment alone does not make it possible to reach the UTS imposed by the ASTM-A494 standard. In this work, the possibility of using stabilization treatment to increase mechanical strength as well was considered. Treatments, with different combinations of time and temperature, were carried out in order to modify the material’s microstructure. After the thermal treatments, microstructural analyses, mechanical tests and (pitting and intergranular) corrosion and resistance tests were carried out to identify optimal treatment parameters in order to promote the evolution of microstructural constituents capable of improving mechanical strength without decreasing corrosion resistance. The treatment that achieves the best compromise between mechanical properties and corrosion resistance is stabilization at 970 °C for 4 h.

Precipitation hardening and intergranular corrosion behavior of novel Al–Mg–Zn(-Cu) alloys

High-performance aluminum alloys are desired for applications that require lightweight materials, but it is challenging to overcome the tradeoff between their strength and intergranular corrosion resistance. To overcome this tradeoff, we have prepared novel Al–Mg–Zn (-Cu) alloys with highly Zn content combined with Cu addition. The alloys with a (Zn + Cu)/Mg ratio below 1.5 are different from traditional 2000, 5000 and 7000 series aluminium alloys. The results show that the number density and lattice spacing of intragranular precipitates increase, while the precipitate sizes decreases with the increase of (Zn + Cu)/Mg ratio, which is the reason for the increase of the alloy strength. Meanwhile, the intergranular corrosion resistance of the alloys is also enhanced by decreasing the potential between grain boundary precipitates and the Al matrix, especially in alloys with high (Zn + Cu)/Mg ratios. These results provide a new method for obtaining high-strength and corrosion-resistant aluminum alloys.

An innovative class of aluminum alloys for automotive industry: investigation on their corrosion resistance

Self-hardening aluminum alloys (AlZn10Si8Mg, EN-AC-71100) represent an interesting innovative class of material for the production of automotive and aerospace components with high-mechanical strength and good corrosion resistance. The aim of the present is related to the investigation of the intergranular corrosion resistance of an innovative class of self hardening alloys. Microstructural characterization combined with compositional analysis has been carried out by Optical and Scanning Electron Microscope equipped with Energy X-rays Dispersive Spectroscopy unit. Three-point bending test and Charpy Impact test have been performed and the corrosion resistance of the alloys has been investigated according to standard BS 11846, method B. The susceptibility of the alloy to intergranular corrosion has been assessed evaluating the maximum corrosion depth and the weight loss of the alloy after corrosion test. The results obtained have been demonstrated that the corrosion resistance of the alloy can be achieved by Mg addition.

Influence of present phases in corrosion and mechanical behavior of UNS S31803 duplex stainless steel welded by conventional short circuit MIG/MAG process

Duplex stainless steel (AID) is an alloy that, by allying both good mechanical properties and excellent corrosion resistance properties, comes increasing industrial interest every day. These attractions make it widely used in the most diverse industrial sectors such as pulp and paper industry, nuclear power, processing, oil and gas, among others. Its wide application in several industrial sectors constantly demands that this material is subjected to some welding process. Its high corrosion and mechanical resistance are attributed to balanced microstructure in approximately 50% ferrite and 50% austenite. In the present work, UNS S31803 AID plates were welded in a 45° bevel by conventional short-circuit MIG/MAG process, using three different weld energies, in the range of 0.5–0.8kJ/mm. The results showed that the effect of the welding energy on the ferrite volumetric fraction was very marked in the heat affected zone (HAZ) and in the weld metal this effect was not so pronounced. The mechanical properties of hardness and corrosion resistance (intergranular corrosion) were evaluated as a function of the welding energy employed. In general, both hardness and intergranular corrosion resistance were not influenced when the various welding conditions were compared. The toughness were evaluated by the crack tip opening displacement technique, compared to the base metal, and the condition 03 (19V) had the best result.

Suppression of intergranular corrosion by surface grain boundary engineering of 304 austenitic stainless steel using laser peening plus annealing

Grain boundary engineering (GBE) has a high potential to suppress intergranular degradation and improve weld properties. Thermomechanical processing is typically used to optimize grain boundary character distributions (GBCDs) for the GBE of face-centered cubic materials with low stacking fault energy. Pre-straining plus annealing has achieved the optimal GBCD for GBE of austenitic stainless steels. Typically, cold rolling is used for pre-straining, but is not suitable for products with complex shapes. Laser peening can introduce strain locally and flexibly, even on complex parts. Therefore, this study attempted to apply laser peening as a pre-straining method during the thermomechanical processing. Several sets of process parameters during laser peening were selected to introduce suitable pre-strain into the surface of a 304 steel specimen based on previous GBE studies focusing on cold rolling plus annealing. Annealing at 1260 K for 48 h following laser peening led to an optimal GBCD with over 80 % frequency for coincidence site lattice boundaries and disconnected random boundaries. An intergranular corrosion test revealed that the laser-peened and annealed 304 steel with an optimal GBCD exhibits excellent intergranular corrosion resistance, which is far greater than that of an as-received sample and comparable to that of a cold-rolled and annealed sample.

Exfoliation and intergranular corrosion resistance of the 2198 Al–Cu–Li alloy with different thermomechanical treatments

AbstractIn 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.

Precipitate microstructures, mechanical properties and corrosion resistance of Al-1.0 wt%Cu-2.5 wt%Li alloys with different micro-alloyed elements addition

The evolution of precipitate microstructures of the Al-1.0wt%Cu-2.5wt%Li alloys with different micro-alloyed elements addition was investigated during ageing at 175 °C together with the mechanical properties and corrosion resistance. It was found that the Al-Cu-Li alloy with Zn addition possesses not only higher yield strength but also improved intergranular corrosion resistance, compared with the alloy with Mg addition. The corresponding precipitate microstructures were greatly affected by Zn or Mg micro-alloyed element addition, for example, with Zn addition the δ′-Al3Li, T1-Al2CuLi and θ′-Al2Cu (and θ″) phases were formed within grains, whereas the coarse TB-Al7Cu4Li phase and the T1 phases appeared at grain boundaries (GBs). In contrast, the Al-Cu-Li alloy with Mg addition possessed the δ′, T1 and S′-Al2CuMg phases within grains, while the coarse AlCu phase and T1 phases were present at GBs. The alloy with combined Zn + Mg addition exhibited a duplex microstructure of the two alloys, resulting in lower mechanical strengths but the intermediate corrosion resistance. Therefore, the increased amount of Zn-containing coarsened TB phase at GBs was found to improve the corrosion resistance of the alloy with Zn addition, due to the smaller potential difference between the GB precipitates and the adjacent zones.

Dependence of microstructure, mechanical properties, and inter-granular corrosion behavior of Al-5.1Mg-3.0Zn-0.15Cu alloys with high temperature pre-treatment

The age-hardenable Al-5.1Mg-3.0Zn-0.15Cu (wt%) alloy in peak-aged condition has high strength but poor inter-granular corrosion resistance. The effect of high temperature pre-treatment on mechanical properties and inter-granular corrosion of the alloy has been investigated via hardness, tensile, inter-granular corrosion depth, and electrochemical testing. The morphology, distribution, and composition evolution of precipitates in the grain and along grain boundaries are characterized and analyzed using transmission electron microscopy. The relationships between mechanical properties, inter-granular corrosion resistance, and microstructure evolution during the high temperature pre-treatment and the subsequent aging process have been established. The inter-granular corrosion resistance is enhanced with decreasing pre-treatment temperature. While the strength increases with increasing of pre-treatment temperature, and it maintains a similar value to that of the T6 temper, when the pre-treatment temperature reaches 410 °C. The 410 °C/1 h + T6 temper can improve the inter-granular corrosion resistance approximately 55% and while simultaneously maintaining a similar strength to that of the T6 temper, which mainly results from preferentially segregated Mg and Zn atoms along grain boundaries and the preservation of the maintained solid solution state in grains after the 410 °C/1 h treatment, respectively. The discontinuity degree of grain boundary precipitates and the concentration difference of Cu element between grain boundary precipitates and adjacent zones have been found to be the key factors to improve the inter-granular corrosion resistance.

Enhancing the intergranular corrosion resistance of high Mg‐alloyed Al–Mg alloy by Y addition

AbstractMicroalloying is thought to improve the performance of Al–Mg alloys commonly used in transport applications. The effect of Y addition (0–0.4%) on the microstructure, mechanical properties, and corrosion resistance of Al–9.2Mg–0.7Mn alloy is investigated for potential use in engineering applications. The generation of the β‐Al3Mg2 phase along the grain boundaries is suppressed in the as‐cast alloy due to the formation of the AlMgY ternary phase. The average intergranular corrosion mass loss of the alloy with 0.1% Y addition decreases about 53.1% almost at no expense of mechanical performance in the as‐rolled alloy after annealing. Moreover, the alloy with 0.1% Y addition shows the corrosion mass loss about 30.2% lower than the Y‐free alloy in the sensitized state. The enhanced corrosion resistance of the alloy can be ascribed to the reduced β‐Al3Mg2 precipitation along the grain boundaries associated with Y addition.

Effect of trace Er on the microstructure and properties of Al–Zn–Mg–Cu–Zr alloys during heat treatments

The effects of trace Er on the microstructural evolution and mechanical properties of newly designed Al–Zn–Mg–Cu–Zr alloys for drilling pipes were investigated. After homogenization, most of the eutectics dissolved into the matrix and some primary phases remained, including Al8Cu4Er, Al12(Mn,Cr), and Al3Ti. Dispersed nano-sized Al3(Er,Zr) precipitates were formed in the Er-containing alloys after homogenization. Following extrusion, solution and retrogression re-aging (RRA) treatment, the hardness and yield strength of the 0.10 wt% Er-containing alloy are increased by 14% (25.4 HV) and 12.7% (70 MPa) compared to the alloy without Er. This improvement could be ascribed to the precipitation strengthening of fine Al3(Er,Zr) particles, which complemented the conventional η' phase precipitation strengthening. The intergranular corrosion resistance of the RRA-treated alloy with the addition of 0.10 wt% Er was improved by 65% due to a lower amount of high angle grain boundaries. The fracture and intergranular corrosion mechanisms in alloys with and without Er addition were linked to the respective grain structures.

Investigation on the precipitation and corrosion behaviour of 19% Cr economical duplex stainless steel with Mn addition by aging at 800°C

ABSTRACT The precipitation and corrosion behaviour of Fe–19Cr–1.6Ni–0.9Mo–0.2N–xMn duplex stainless steel was investigated aging at 800°C. With more Mn addition, the precipitation changed from χ-phase to σ-phase by prolonging aging time to 54 h, and the accelerating of aging induced σ-phase precipitate is mainly due to its partition by Mn. The addition of Mn from 3.6 to 5.5 wt-% decreased pitting corrosion resistance due to its detrimental effect on pitting resistance equivalent numbers, but the trend does not conform to the experimental result with Mn addition of 8.1%. The decrease in intergranular corrosion resistance mainly depends on the increase in precipitates number along δ/γ grain boundaries. It is beneficial to increase repassivation ability with higher Mn addition in early aging time,and the passivation film resistance was more sensitive to precipitate compared with more Mn addition.

Enhancing the Intergranular Corrosion Resistance of High-Nitrogen-Containing 316L Stainless Steels by Grain Boundary Engineering via Thermomechanical Treatment

High-nitrogen-containing Type 316L stainless steels (SS) with 0.12% to 0.22% N are being developed as future structural material of fast breeder reactors because of their improved hardness and resistance to localized corrosion. However, stainless steels with higher nitrogen content are prone to intergranular corrosion (IGC) due to their tendency to get sensitized by enhanced precipitation of Cr2N. Thermomechanical treatment (TMT) of 6.5% cold-work and heat-treatment (1,323 K for 30 min) is evaluated in this study to enhance IGC resistance of 0.07%, 0.12%, 0.14%, and 0.22% nitrogen-containing Type 316L SS. The frequency of coincident site lattice (CSL) boundaries is found to increase with increase in nitrogen content in Type 316L SS. A maximum CSL increase of 35% was seen in 0.22% nitrogen containing stainless steel, as compared to samples containing 0.07% to 0.12% N. The effective grain boundary energy was the least (<0.1 μm−1) for Type 316L SS containing 0.22% N, which is attributed to the higher percentage of Σ3 boundaries. Double-loop electrochemical potentiokinetic reactivation (DL-EPR) tests conducted on the sensitized as-received and TMT samples showed a clear decrease in sensitization for TMT samples. The improved resistance to IGC visualized in the post-DL-EPR optical micrographs of TMT samples is attributed to the breakdown in the connectivity of attacked boundaries. The role of nitrogen in austenitic SS on twinning and generation of CSL boundaries is also discussed.

Enhancing the Corrosion Resistance of Al-Cu-Li Alloys through Regulating Precipitation.

The influences of aging treatments on microstructures and the corrosion properties of an Al–Cu–Li alloy were investigated through an immersion test in intergranular corrosion (IGC) solutions, a potentiodynamic polarization test, and electrochemical impedance spectra (EIS), combined with scanning and transmission electron microscopy. The results demonstrated that the Al–Cu–Li alloy displayed outstanding comprehensive mechanical properties and IGC resistance after treating with pre-strain deformation and a double aging process (PDA). Both the PDA and pre-strain followed by creep aging (PCA) treatments significantly increased the number densities of T1 and θ’ precipitates in the grain interior. The increase in precipitates in the grain interior greatly reduced the Cu-rich precipitates on the grain boundaries and inhibited the formation of a precipitate-free zone (PFZ). The electrochemical characteristics of the Al–Cu–Li alloy were influenced by the precipitates in the grain interior and grain boundaries. The studied alloy gained high IGC resistance due to the refinement of its microstructure, and the main corrosion mode was intra-granular pitting corrosion; thus, the corrosion diffusion rate was slowed down.

Current-driving intergranular corrosion performance regeneration below the precipitates solvus temperature in Al–Mg alloy

Heat treatment is an effective method to improve the intergranular corrosion resistance of the sensitized Al–Mg alloy due to dissolution of the grain boundary precipitates above the solvus temperature of β-phase. The grain boundary precipitates will grow and coarsening below the solvus temperature. In this study, the in-situ intergranular corrosion performance regeneration of the sensitized Al–Mg alloy can be realized by low-density electro-pulsing treatment below the solvus temperature of β-phase. Our findings show that the dissolution of grain boundary precipitates by electro-pulsing treatment is accelerated at relatively low temperature in comparison to traditional heat treatment. The athermal effect produced by the interaction between atoms and electrons on the dissolution of grain boundary precipitates is the main reason for the improved corrosion resistance below the solvus temperature of β-phase.

Effects of non-isothermal aging on microstructure, mechanical properties and corrosion resistance of 2A14 aluminum alloy

Abstract The microstructure, mechanical properties and intergranular corrosion (IGC) resistance of 2A14 aluminum alloy subjected to several non-isothermal aging (NIA) treatments have been investigated. When target aging temperature is 210 °C during NIA, the hardness at the heating rate of 10 °C/h are higher than that at the heating rate of 20 °C/h. A slight decline of hardness occurs when the temperature is beyond 200 °C during the heating stage of NIA process, while the hardness turns its step to improve at approximately 140 °C at the cooling stage. This is due to the mutual competition between the coarsening of precipitates and secondary precipitation during the cooling process. Compared with isothermal peak (T6) aging temper, The NIA process ((40–210, 10 °C/h) + (210–180, 20 °C/h)) makes the elongation and impact toughness of 2A14 aluminum alloy increase by 6.5% and 4.4%, respectively, while yield strength and fracture strength remain about the same. The co-precipitation of θ′ and Q′ precipitates can be observed for various aging conditions, but different from T6 aging, the NIA process leads to the high-density θ′ precipitates with wider length range. This characteristic of θ′ phase contributes to better mechanical performance of 2A14 aluminum alloy after the NIA process. In addition, the IGC resistance of the non-isothermal aged 2A14 alloy slightly decreases compared with that after T6 aging, which is closely linked with the widening of PFZ and the increase of potential difference between the PFZ and the matrix after the NIA process.

Corrosion, Wear and Mechanical Properties of Boron Added Cast 304 Stainless Steel

The main objective of this research was to examine the effect adding B at 0, 100, 170 ppm had on the mechanical properties, wear and corrosion behaviour (in two different corrosive media) of cast 304 stainless steels. The microstructures, wear surface and corrosion morphologies were examined by optical microscopy, X-ray diffraction analyses and scanning electron microscopy (SEM). The cast 304 stainless steels with boron addition as 0, 100, 170 ppm, were used to investigate their corrosion behaviours by electrochemical potentiodynamic polarisation capacities in 5% HCl and 5% HNO3 solutions at laboratory environment. Wear tests were conducted in a pin-on-disc type wear tester. Optimum properties in relations of improved strength and wear resistance without loss in hardness were obtained when the cast 304 stainless steel contained 100 ppm B. At B contents higher than 100 ppm decrease of the hardness was accompanied an increase in strength and wear resistance. It was found that wear loss cast 304 stainless steel with B addition decreased with the increase of sliding distance, when compared with 0 ppm B addition cast 304 stainless steel. With regard to results of the corrosion experiment, Icor tended to decrease the addition 110 ppm B in 5% HCl solution, leading to a rise in the corrosion resistance. Adding B to the cast 304 stainless steels helped to enhance its corrosion resistance, except that its intergranular corrosion resistance reduced, which can be seen by examining the corrosion morphology. The improved wear behaviour and corrosion resistance of cast 304 stainless steel was attributed to the adding boron cast 304 stainless steel.

Corrosion Behavior and Mechanical Properties of AISI 316 Stainless Steel Clad Q235 Plate

This paper deals with carbon steel and stainless steel clad-plate properties. Cladding is performed by the submerged-arc welding (SAW) overlay process. Due to element diffusion (Fe, Cr, Ni, and Mn), a 1.5 mm wide diffusion layer is formed between the stainless steel and carbon steel interface of the cladded plate affecting corrosion resistance. Pitting resistance is evaluated by measuring the critical-pitting temperature (CPT), as described in the American Society for Testing and Materials (ASTM) G-48 standard test. Additionally, Huey immersion tests, in accordance with ASTM A262, Type C, are carried out to evaluate the intergranular corrosion resistance. Some hardness peaks are detected in microalloyed steel close to the molten interface line in the coarse-grained heat-affected zone (CGHAZ). Results show that stress-relieving treatments are not sufficient to avoid hardness peaks. The hardness peaks in the CGHAZ of the microalloyed steel disappear after quenching and tempering (Q and T).

Corrosion resistance of stainless steel layer prepared by twin-wire indirect arc surfacing welding

Twin-wire indirect arc welding(TWIAW) has advantages of high deposition efficiency and low dilution rate. Compared to traditional MIG welding, the molten pool solidifies more rapidly, influencing final microstructure and associated corrosion resistance property. The intergranular corrosion resistance and the pitting corrosion resistance of stainless steel surfacing layer prepared by TWIAW were investigated through electrochemical testing. The semiconductor characteristics of formed passive film were analyzed by Mott-Schottky curves. The stainless steel surfacing layer prepared by TWIAW achieved higher resistance to intergranular corrosion and pitting corrosion, compared to that of MIG surfacing layer. In addition, the carrier concentration in passivation film of TWIAW surfacing layer was also significantly lower than that of the MIG layer. The larger cooling rate of TWIAW layer improved homogeneous solidification microstructure, which led to better corrosion resistance properties.

Effect of Trace Elements on the Crystallization Temperature Interval and Properties of 5xxx Series Aluminum Alloys

The influence of alloying elements Er, Zr, Cu, Si and Zn on the crystallization temperature interval, microstructure, mechanical properties and corrosion behavior of Al-Mg-Mn alloy were studied by differential scanning calorimetry (DSC), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), tensile testing, electrochemical measurements and nitric acid mass loss test (NAMLT). The results show that the crystallization temperature range of Al-Mg-Mn alloy with addition of Zn decreased 4.7 °C. Cold rolled alloys mainly contain S texture, Copper texture, Brass texture, and Goss texture; the content of the S texture is the highest. With the addition of trace elements, the second phase Al3Er, Al3Zr, Al2CuMg, Mg2Si and MgZn2 can be formed, which can improve the tensile strength and yield strength of Al-Mg-Mn alloy. The addition of the alloying element Zn can also improve the intergranular corrosion resistance of the Al-Mg-Mn alloy.