Search Results (230)

A comparative investigation of the corrosion behavior evolution of 15%SiCp/Al-Cu-Mg aluminum matrix composites (AMC) subjected to different heat treatments in a salt spray environment containing 5wt% NaCl was performed. Metallographic microscopy was used to observe the surface morphology of the corroded materials. Field-emission transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used for microstructural evaluation and elemental analysis of the samples. Polarization curves and electrochemical impedance spectroscopy (EIS) were also employed to investigate the corrosion performance of the particle-reinforced aluminum matrix composites under different heat treatments. The test results indicate that, in addition to the influence of various grain boundary precipitates and electrochemical inhomogeneities between the precipitate-free zone (PFZ) and the aluminum matrix, differences in electrochemical properties between the SiC reinforcement particles and the aluminum alloy matrix are also a primary factor contributing to the corrosion of the aluminum-based composites in a 5wt% NaCl salt spray environment. Microstructural observations and electrochemical testing of AMC specimens at different corrosion stages indicate that under-aged samples exhibit relatively higher intergranular corrosion susceptibility. Under prolonged exposure to a salt spray environment, the over-aged specimen exhibited more pronounced galvanic corrosion phenomena, specifically, a significant decrease in Charge transfer resistance (R_ct) values and an increase in CPE values. R_ct results indicate that naturally aged AMC exhibits higher corrosion resistance than artificially aged AMC. With increased salt spray corrosion time, varying degrees of crevice corrosion occurred at the Al–SiC interface in all heat-treated samples. Full article

While cost-effective austenitic stainless steels like AISI 304 are utilised in intermediate-temperature concentrated solar power (CSP) components, autogenous welding can compromise their structural integrity. This work investigates the corrosion behaviour of autogenous TIG-welded AISI 304 joints exposed to commercial molten solar salt at 550 °C for up to 1350 h under static conditions. Gravimetric and microstructural analyses revealed a stochastic bimodal breakaway oxidation mechanism. After an initial transient passivation regime (0–650 h) attributed to the formation of a protective Fe₃O₄/FeCr₂O₄ bi-layer, a sharp kinetic acceleration occurred. This localized breakdown was synergistically catalysed by trace chloride impurities, which triggered deep pitting along the microsegregated dendritic networks of the weld metal. Furthermore, due to severe X-ray attenuation under massive late-stage oxides, definitive proof of sensitisation was established using the standardised ASTM A262 Practice A topographic evaluation. The appearance of continuous ditch structures only in the heat-affected zone (HAZ) suggests severe intergranular anodic dissolution. This failure is thermodynamically driven by unmitigated residual tensile stresses, highlighting that the long-term reliability of these components is interpreted to be dictated by the localised, asymmetric breakdown of the weldment rather than uniform global oxidation. Full article

This study investigated the effects of double aging processes on the tensile properties and salt spray corrosion resistance of an Al-Zn-Mg-Cu alloy. The mechanisms by which microstructural evolution influences these properties were elucidated using tensile testing, salt spray corrosion testing, electrochemical measurements, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicate that, under double aging processes, increasing the duration or temperature of either the first- or second-stage aging leads to a slight decrease in tensile strength but a significant improvement in salt spray and electrochemical corrosion resistance. This is attributed to the gradual coarsening of intergranular and grain boundary precipitates, a decrease in their number density, and a widening of the precipitate-free zone (PFZ). Furthermore, the second-stage aging exerts a more pronounced influence on the alloy’s properties and microstructure than the first-stage aging, and their quantitative contributions are systematically distinguished. The alloy treated with the 110 °C/3 h + 155 °C/20 h double aging processes exhibits the optimal overall performance, achieving a better balance between strength and corrosion resistance compared to conventional T6 treatment. Full article

The precipitation characteristics and grain-boundary structure of Al–Cu–Mg alloys strongly affect their corrosion behavior, whereas the roles of Si and Ag microalloying in low Cu/Mg ratio systems are not yet fully understood. In this work, the effects of Si and Ag additions on age-hardening response, precipitation characteristics, and corrosion performance were systematically investigated by combining transmission electron microscopy with electrochemical and corrosion measurements. Si addition significantly accelerated the age-hardening kinetics, enabling the alloy to reach a hardness of 147 HV after only 6 h of aging, whereas the base alloy required 24 h to reach a similar level. This accelerated response was accompanied by refined S-phase precipitation and a markedly narrowed precipitation-free zone along grain boundaries. Further Ag addition introduced coherent Ω precipitates and a more complex multi-phase precipitation structure, which increased microstructural heterogeneity. As a result, the Al–Cu–Mg–Si alloy exhibited the lowest corrosion current density and the shallowest corrosion depth, whereas the Al–Cu–Mg–Si–Ag alloy showed deteriorated corrosion resistance. These results indicate that Si microalloying alone can simultaneously accelerate aging and improve corrosion resistance, while further Ag addition enhances precipitation complexity and strengthening potential but increases susceptibility to localized corrosion. Full article

As a key component in oil drilling, drill pipes are prone to failure in harsh operating service environments. Multiple severe cracks were identified in the S135 drill pipes following field service, with partial crack extensions of ~1 mm detected at the thread roots penetrating into the pipe wall, posing critical threats to structural integrity. This study investigated the failure mechanisms of the drill pipes and examined the potential effects of dynamic rotation on corrosion-assisted cracking. The results showed that this failure was close to the combined results of corrosion and torque. Cl⁻ and S²⁻ in the drilling fluid were the main sources of corrosive substances. Cl⁻ preferentially accumulated on the drill pipe surface, initiating localized pitting corrosion. Under applied stress, these surface pits exacerbated local stress concentration. The synergistic action of S²⁻ then promoted the transition from pitting to stress corrosion cracking. Regarding the corrosion stage, the rotational state of the drill pipe will affect the drilling fluid’s corrosion results. The mud deposition during rotation leads to severe intergranular corrosion, which further causes material peeling. Dynamic rotation at 60 r·min⁻¹ increased the corrosion rate to 0.55 mm·a⁻¹ after 216 h of immersion, 41% higher than under static conditions, while maximum corrosion depth increased from 8.43 μm to 13.86 μm. These results indicate that rotational motion accelerates corrosion-assisted cracking. Full article

The performance of flux-cored Zn-Al filler metal is susceptible to corrosion-induced degradation, thereby impairing its brazability. In this study, flux-cored Zn-2Al filler metals are prepared, and the salt spray test is subsequently carried out on the prepared filler metals. Scanning transmission electron microscope is used to identify the phases in filler metals. An electrochemical workstation was employed to test the electrochemical performance of the filler metals. The corrosion pathways and evolution patterns of filler metals are analyzed. The findings demonstrate that the corrosion type of the filler metals is electrochemical corrosion, characterized primarily by the corrosion modes of pitting corrosion and intergranular corrosion. The cathode is the α-Al phase, which undergoes an oxygen-absorption corrosion reaction, while the anode is the η-Zn phase, which experiences corrosion and subsequent dissolution. The continuously distributed α-Al phase bands and discontinuously distributed large-sized rod-like α-Al phases accelerate the corrosion rate, and the corrosion propagation rate along the extrusion direction is higher than that in the radially inward direction. After 15 days of salt spray corrosion, the tensile strength of filler metals decreases by 16.2%, and the elongation rate decreases to 3.73%. Full article

Intergranular corrosion (IGC) and exfoliation corrosion (EXCO) limit the durability of 2219 Al–Cu in chloride-rich, cyclic-humidity aerospace environments, and conventional thermal stress relief can worsen grain boundary precipitates and grain boundary non-precipitation zones (PFZs), motivating evaluation of low-temperature resonant vibration stress relief. Using polarization tests and microstructural analysis, we show that RRV lowers corrosion current, strengthens passivation, and reduces IGC and EXCO susceptibility. Alternating tensile–compressive stresses build dislocation networks that convert continuous or semi-continuous grain boundary precipitates into discrete distributions, increasing corrosion path tortuosity and slowing intergranular attack. A more discrete cathodic phase, a narrowed solute-enriched anodic band, and reduced PFZs disrupt corrosion channel continuity, weaken microgalvanic driving forces via a more uniform θ′ distribution, and limit corrosion product wedging, while homogenized precipitates suppress local galvanic coupling in EXCO-like media. Overall, RRV synergistically optimizes dislocation configuration and precipitate redistribution to intrinsically enhance corrosion resistance and offers a practical, low-temperature, scalable route to improve the durability of high-strength aluminum alloy structures in aerospace service. Full article

Axial cracking in threaded joints of rotary steerable tools is a critical but under-investigated failure mode that can severely disrupt shale gas drilling operations. Understanding its root cause is essential for prevention. This study aims to determine the cause of an axial cracking failure in an S35150 austenitic stainless steel threaded joint from a field operation. A comprehensive analysis was conducted, integrating physicochemical characterization of the failed joint. The stress corrosion behavior of the threaded joint in a simulated corrosive environment was evaluated via four-point bend (FPB) and double cantilever beam (DCB) stress corrosion tests. The results showed that the material exhibited high susceptibility factors: a hardness of 38.5 HRC, a yield-to-tensile ratio near 1, and a P content exceeding the standard. Fracture surface analysis revealed an intergranular morphology with substantial chlorine (0.78%) and sulfur (0.93%) contents, indicative of stress corrosion cracking (SCC). The laboratory tests results demonstrated that the threaded joint had poor crack resistance: the fracture toughness value of the specimen measured by the DCB test was 24.14 MPa·m^0.5, and all specimens fractured during the FPB. Full article

Pure tantalum (Ta) is widely used in applications such as capacitors and semiconductor coatings due to its high melting point, excellent corrosion resistance, and good biocompatibility. In this study, spark plasma sintering (SPS) technology has been employed to successfully prepare high-density, fine-grained pure Ta through systematic optimization of sintering temperature, pressure, and holding time. The results indicate that sintering temperature plays a predominant role on the densification behavior. Increasing the sintering pressure and prolonging the holding time also contribute to further enhancing the densification. Under the process conditions of 1450 °C, 40 MPa, and a holding time of 10 min, the relative density of the sample reaches 98.7%. Microstructural analysis reveals that the sintering process of pure Ta can be divided into two main stages: densification-dominated and grain growth-dominated. When the relative density exceeds a threshold value (approximately 96% in this study), the grain size increases rapidly from 4.43 μm to 28.87 μm. This grain coarsening leads to a transition in the fracture mechanism from a mixed mode of intergranular and cleavage fractures to completely intergranular fracture, which significantly reduces the bending strength and plastic deformation capacity of the material. Full article

This study investigates the comparative effects of unidirectional (R1) and reversible (R2) rolling processes on the corrosion resistance of 430 stainless steel, specifically evaluating the roles of residual stress versus microstructural stability. The experimental approach involved microstructural characterization of processed samples followed by corrosion performance evaluations, including salt spray testing and post-corrosion morphological analysis. The results indicate that R1 processing produces a dense, aligned microstructure with high residual stress, whereas R2 rolling leads to cyclic stress dissipation but results in extensive carbide delamination and surface porosity. Despite its higher residual stress, the R1 sample demonstrated significantly higher corrosion resilience. In contrast, the R2 sample exhibited pronounced localized degradation, characterized by deep intergranular cavities and intragranular attack. The findings reveal that microstructural voids and interfacial stability, rather than residual stress levels, are the primary factors governing passive film rupture and pit nucleation in these rolling conditions. The study demonstrates that unidirectional rolling preserves microstructural coherence, thereby enhancing the overall corrosion resistance of 430 stainless steels. Full article

Incoloy 800H is important structural alloy for heat exchange tubes of Generation IV nuclear power systems. Revealing the key heat treatment effects on the microstructure and corrosion behavior of 800H is a key issue for its performance optimization and safe application in IV nuclear power industries. This work investigated the solid solution heat treatment–microstructure–corrosion resistance relationship using various electrochemical corrosion techniques and morphology characterizations. The results showed that 1120 °C was an insufficient solid solution heat treatment temperature for 800H, at which 800H demonstrated uneven enlargement of grains and undissolved Cr-carbides, which resulted in fast corrosion. 800H demonstrated even growth of grains with best grain uniformity and dissolution of Cr-carbides at 1150 °C, thus showing the best corrosion resistance. However, the further increase in solid solution temperature to 1180 °C resulted in excessive grain growth and severe intergranular corrosion (IGC) attack. This work deepened the understanding of the corrosion mechanism of 800H and provided data for its performance optimization. Full article

The operational integrity of L415 pipeline steel, a critical component of China’s energy network, is severely threatened by the unique acidic red soil environments prevalent in Southern China. A significant knowledge gap exists regarding its specific failure mechanisms, particularly the interplay between Anodic Dissolution (AD) and Hydrogen Embrittlement (HE) in driving Stress Corrosion Cracking (SCC). This study systematically investigates the corrosion and SCC behavior of L415 steel in a simulated environment that replicates the typical soil chemistry of the Gannan region in Southern China. Results revealed that corrosion kinetics are highly dependent on environmental chemistry, with corrosion rates escalating nearly four-fold from 0.0505 mm/a to a severe 0.1949 mm/a, driven by the synergy of low pH and high SO₄²⁻ concentration. This behavior is governed by the integrity of the corrosion product film, where aggressive environments form porous, unprotective layers with low charge transfer resistance. Slow strain rate tensile (SSRT) tests confirmed that the steel’s susceptibility to SCC is strongly promoted by acidity. Critically, the dominant SCC mechanism was environment-dependent, transitioning from Hydrogen Embrittlement (HE) to intergranular cracking in the most acidic environment, and a mixed AD-HE mechanism causing transgranular cracking in high-chloride conditions. These findings provide a direct mechanistic link between soil chemistry and failure mode, offering a crucial scientific basis for developing environment-specific integrity management strategies for pipelines in these challenging terrains. Full article

This study investigates the effects of welding current on the microstructure, mechanical properties, and corrosion behavior of 7075/7075 pulsed metal inert gas (P-MIG) welded joints. Welding experiments were conducted at currents of 190 A, 200 A, and 210 A using ER5356 filler wire, with the joints analyzed through optical microscopy (OM), scanning electron microscopy (SEM/EDS), and tensile and hardness testing, as well as intergranular and electrochemical corrosion evaluations. The results reveal that increasing welding current alters the solidification dynamics and precipitation behavior in the WZ. At 190 A, refined and uniformly distributed dendrites were obtained, whereas at 210 A, grains coarsened and elemental segregation was more pronounced. The weld hardness exhibited a trend of first increasing and then slightly decreasing with increasing welding current, with a maximum value of 99.5 HV0.1 obtained at 200 A. Similarly, the tensile strength improved with increasing welding current, reaching 257.7 MPa with 8% elongation at 210 A. Corrosion resistance exhibited a non-monotonic trend, with the best performance observed at 200 A, as indicated by the shallowest intergranular corrosion depth, the most positive open-circuit potential, and the highest charge transfer resistance in electrochemical impedance spectroscopy. The findings demonstrate that welding current is a critical parameter controlling the balance between microstructural refinement, mechanical strengthening, and corrosion resistance, and that 200 A represents the optimal condition under the investigated parameters. These insights provide theoretical guidance and experimental evidence for process optimization in the welding of high-strength aluminum alloys. Full article

The high-Mg-content Al-Mg-Zn-Si alloy, as a novel aluminum alloy, exhibits excellent strength, toughness, and corrosion resistance, demonstrating significant application potential in lightweight structural components for aerospace, weapon systems, rail transportation, and other fields. In this study, friction stir welding was employed to weld the high-Mg-content Al-Mg-Zn-Si alloy. Subsequent aging treatment was applied to establish the relationship between the mechanical properties and microstructural characteristics of the welded joint, aiming to elucidate the strengthening mechanisms of the new alloy and provide insights for achieving high-quality welds. The results indicate that the microhardness profile of the as-welded joint exhibited a “W” shape, with overall low hardness values and minor differences between zones. After the aging treatment, the microhardness increased significantly in the base material (BM), the thermo-mechanically affected zone (TMAZ), and the stir zone (SZ), whereas the heat-affected zone (HAZ) adjacent to the SZ exhibited only a marginal increase, making it the softest region in the aged joint. The yield strength and ultimate tensile strength of the aged joint increased to 327 MPa and 471 MPa, respectively. The enhancement in microhardness and strength after aging treatment was attributed to the precipitation of numerous nano-sized T-phase particles within grains. Interestingly, the tensile samples of the aged joint fractured in the high-hardness SZ instead of the low-hardness HAZ. This fracture behavior was primarily attributed to continuous grain boundary precipitates, which reduced intergranular cohesion. In contrast, the elongated grain structure in the HAZ more effectively resisted intergranular crack propagation compared to the equiaxed grains in the SZ. Full article

A new experiment was conducted to determine the corrosion rates of different geometric structures (vertical plate, horizontal plate, cube, and sphere) with the same surface area of pure magnesium in a saltwater immersion environment of 3.5% NaCl for 108 h, illustrating a clear geometry effect arising from local boundary layer water flow. Magnesium was chosen as an idealized material because of its small electrochemical potential. The different corrosion mechanisms were analyzed and quantified by measuring the surface roughness (localized corrosion) via laser profilometry, mass loss (general corrosion) by weighing specimens, localized and intergranular corrosion via Scanning Electron Microscopy and Optical Microscopy, and total corrosion via hydrogen measurements. Although the corrosion rates were very similar at the beginning of the tests, the vertical and horizontal plates gave corrosion rates greater than the cube and sphere shortly after the tests started. Water circulation induced by hydrogen gas bubbles caused a greater corrosion rate at the edges of the plates and cube. These results indicate that a structure’s geometric edges should be made smoother to lessen corrosion effects in design. Also, when one is designing for corrosion resistance of a structural component, our results demonstrate that the designer must consider the fluid dynamics in the boundary value problem surrounding the structural component, since the geometric shape changes the corrosion rate. Full article