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•Microstructural studies of 2524-T3 Al alloy welded by FSW were performed.•Corrosion resistance of the base material and nugget zone was assessed by EIS and SVET.•Base material and ...nugget zone possess a cathodic behaviour.•The influence of FSW process on FCG curves in nugget and base material was studied.
The corrosion processes and its influence on the FCG curves of the 2524-T3 alloy joined by FSW was studied in the nugget and BM. To assess the corrosion process, SVET, pH micro-potentiometry and EIS were used. The localised corrosion results showed similar BM and nugget zone electrochemical behaviour, while the TMAZ/HAZ region was electrochemically the weakest zone, susceptible to anodic dissolution. The FSW process and saline environment was found to modify the BM and nugget FCG resistance, being more detrimental for the BM due to the primary IM particles that are not present in the nugget, making it chemically more homogeneous.
•AA2198-T851 is a potential substitute for AA2524-T3 with higher pitting resistance.•AA7081-T73511 is more prone to pitting corrosion than the AA7050-T7451.•Cathodic Al7Cu2Fe particles promote ...dissolution of adjacent 7XXX matrix.
The 2XXX and 7XXX series aluminium alloys are commonly used in aircraft applications where high strength-to-weight ratios are required. The present study aims to compare the corrosion resistance of two novel alloys developed for aircraft industry (AA2198-T851 and 7081-T73511) to that presented by the alternative base alloys (AA2524-T3 and 7050-T7451, respectively). Results indicate that AA2198-T851 may show a superior corrosion performance compared to AA2524-T3, being a potential candidate for its replacement, due to best mechanical properties. In what concerns the 7081-T73511, its resistance to pitting corrosion may be lower than for the base line alloy 7050-T7451.
•Alloy AA2050-T84 presented superior behavior when tested in air and aqueous saline environments.•Electrochemical characterization results showed a superior resistance of alloy AA2050-T84 in saline ...environments.•AA2050-T84 showed signs of non-homogeneous deformation behavior at the crack tip.
AA7050-T7451 aluminum alloy is one of the most used material in aeronautical applications due to its high strength/density ratio and good fatigue resistance. More recently the AA2050-T84 alloy was introduced due to its reduced density and comparable static mechanical properties. However, fatigue crack propagation properties in corrosive environments are yet to be documented. In this paper fatigue crack propagation was evaluated in saline (3.5 wt% NaCl solution) and air environments. The AA2050-T84 alloy presented a better fatigue performance both in air and aqueous saline environments. Its superior performance was ascribed to non-homogeneous deformation and higher corrosion resistance. These results show the AA2050-T84 alloy as a potential candidate to replace AA7050-T7451 alloy in aeronautical components subjected to fatigue in corrosive environments.
The use of friction stir welding (FSW) has proven to be an excellent alternative to join engineering components. Although FSW has had a significant development in recent years, challenges for new ...applications have been raised, such as offshore steel parts suffering hydrogen embrittlement in the gas and oil industry. Therefore, in this work, the microstructure, corrosion, and hydrogen-induced cracking were investigated in a two-pass FSW welded joint of API 5L X70 pipeline steel. The electrochemical results indicate an inhibitory effect on corrosion reaction because of a carbonate product generation in the steel surface. The polygonal ferritic and degenerated pearlite bands microstructure in the base metal fixed carbonate deposits in the steel surface. In the welded regions, the bainitic microstructure and the carbide particle distribution are less efficient in setting the weld surface carbonate deposit. HIC tests showed cracks initiation and propagation to be more prone in hard phases.
•FSW resulted in different type of microstructures delivering different corrosive responses.•The FSW regions presented a higher susceptible to hydrogen induced cracking than base metal.•The BM shows better corrosion resistance than the FSWeld regions in alkaline solution.•LEIS maps showed that the FSWeld regions formed a galvanic cell.
Fracture toughness of natural fibers/castor oil polyurethane composites was investigated. The main interest in studying these biomass composites arises from the fact that both fibers and matrix are ...derived from renewable resources and the formed composite constitute an attempt towards environmental preservation. Sisal and coconut short fibers and woven sisal fabric were used ‘in natura’ and sodium hydroxide treated. The best fracture toughness performance was displayed by the sisal fabric composite. The alkaline treatment showed to be harmful for fracture toughness of the sisal fiber composites since the improved interfacial adhesion impaired the main energy absorption mechanisms. On the other hand, an enhancement on the fracture toughness of coconut fiber composites was observed, which has been credited to the fibrillation process occurring under the severest condition of the alkaline treatment, which creates additional fracture mechanisms.
The effects of Ti, Ni, Mo and Cr on microstructural development, and the chemical composition of the non-metallic inclusions, in high strength low alloy multipass (HSLA) weld metal have been ...considered. Increasing titanium content, in the range of 50 to 400 ppm, has not caused any major effects on microstructural development. With a further increase in the hardenability, by Ni, Mo and Cr additions, the microstructure has changed from a mixture of allotriomorphic ferrite, Widmanstätten ferrite, acicular ferrite and microphases to a mixture of acicular ferrite, bainite, low carbon martensite and microphases. In weld metals with low titanium content, manganese and silicon were the main chemical elements present in inclusions. Increasing the titanium content in the weld metal leads to an increase in the titanium content of the inclusions. For a very high titanium content, ≈
700 ppm, the amount of titanium in the inclusions varies in the range of 60 to 70 wt.%.
The manufacturing of polytetrafluoroethylene products is usually carried out by cold isostatic and/or uniaxial pressing of the powdered polymer, followed by sintering of the “green” parts. During ...pressing, the air initially present in the loose powder leads to the formation of defects in the material, but the mechanisms involved are not entirely understood. The aim of this study was to better understand the role played by the entrapped air during the cold pressing of polytetrafluoroethylene powder. Observation of the microstructure and determination of some mechanical properties of green and sintered samples, manufactured with different quantities of entrapped air by the cold isostatic pressing process, were carried out. The analysis indicated that defects are formed when the entrapped air pressure in the pressed part leads to internal stresses exceeding the intergranular cohesion resistance of the green part. These defects remain in the microstructure even after sintering, considerably reducing the mechanical strength.
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•The entrapped air plays a major role in the defects formation in the sintered PTFE.•An analytical model was used to predict the formation of defects on green material.•Mechanical properties of the PTFE pressed with air extraction was greatly enhanced.•Presence of warts on the fracture surface reveals processing defects in components.
Shot peening is a surface treatment used in components to improve fatigue properties. Usually, this process is performed at room temperature. However, new studies present the possibility of ...performing this surface treatment above room temperature in order to increase the fatigue strength even further, due to a better association of higher plastic deformation with residual stresses. The purpose of this research was to study the effects of the shot peening process at room temperature, on the fatigue performance of SAE 5160 leaf spring steel which is used by the automotive industry. Three-point bending fatigue tests were performed on specimens with the same geometry as the original component. The specimens were shot peened at 25, 100, 150, 200, 250 and 300 °C. It has been observed that the tests performed at higher temperature caused an increase in surface roughness and decreased the residual stress levels. The residual stress values increased for shot-peened specimens at temperatures up to 100 °C and decreased continuously for temperatures above this.
The hydrogen embrittlement (HE) leads to severe steel degradation of mechanical properties. The hydrogen atoms diffuse into the steel and get positioned into reversible and irreversible trap sites. ...The pipe to transport oil and gas needs to be welded to construct long‐distance pipeline projects; thus, friction‐stir welding (FSW) has proven an excellent alternative to joining these pipelines. Therefore, this work assessed and analyzed the influence of hydrogen on the microstructure and fracture toughness of API 5L X70 steel welded by friction‐stir welding. The in‐service conditions were simulated by charging the specimen electrolytically in a 3.5% NaCl water solution with an intensity current of 2 mA·cm−2. According to fracture toughness tests, the base metal (BM) was more affected by hydrogen embrittlement than the friction‐stir zone (SZ), with a fracture toughness reduction of 20% after hydrogen charging. The SZ fracture toughness did not statistically show changes in hydrogen charging by the used times; however, the fracture mechanism changed from ductile to brittle‐like after 4 days of charging. The SZ depicted a better fracture toughness than BM due to the bainitic microstructure, a significant amount of irreversible hydrogen trapping.
Highlights
The influence of hydrogen embrittlement on the FSW welded steel joints was studied.
Fracture toughness on hydrogen embrittlement is affected by FSW microstructure.
The hydrogen charging reduces the ductility in the FSW steel joints.
The embrittlement affected the base metal more than the stir zone.
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