Al7Si0.5Cu0.3Mg(0.3–1)Ni alloys were investigated for elevated temperature performance. It was found that while the yield strength of the overaged alloys at 300°C increased with Ni, the creep ...resistance decreased. Microstructural observations revealed that the brittle interdendritic Τ-Al9FeNi intermetallics undergo severe cracking in the early stages of creep deformation, which weakens the interdendritic regions and leads to a decrease in creep resistance. This study shows that Mn additions modify the Τ-phase preventing cracking during creep and increase the creep resistance.
In this study, an energy-saving and highly efficient high-density pulsed electric current (HDPEC) method was used to improve the formability of the aluminum alloy A6061 after T6 heat treatment ...(A6061-T6). An interrupted tensile test was performed, and the HDPEC treatment was applied after tensile deformation. The results showed that the ductility of A6061-T6 improved by approximately 33% after three HDPEC treatments. The Vickers hardness and residual stress were measured to investigate the effect of the pulsed electric current on formability, and they were recovered after HDPEC treatment. Furthermore, the microstructural morphology and dislocation density were investigated to understand the mechanism of formability enhancement. Detailed analysis shows that the formability enhancement of A6061-T6 after HDPEC treatment is mainly attributed to dislocation elimination, while grain size and crystalline orientation changes are side effects. In addition, the results of equivalent heat treatments demonstrate that the athermal effect of the HDPEC treatment plays a crucial role in the removal of dislocations. Thus, due to the contribution of the athermal effect, HDPEC treatment realizes the advantages of low consumption and high efficiency, and can be dedicated to green processing and manufacturing of metallic materials.
In this study, a number of numerical simulations have been performed to analyze the distribution characteristics of residual stress (RS) in the wire and arc additive manufacturing (WAAM) components ...made of aluminum alloys. Experiments have been performed to measure temperature results (thermal cycles, etc.), residual stresses, and deformation for verification. The results show that the variation in the height of beam can affect the magnitude and distribution of longitudinal RS in both the substrate and the beam, while that can only influence the transverse RS in the substrate but not in the beam nearly. The longitudinal RS on the top surface of the last layer in the WAAM parts changes from tension to compression if the height of beam is above a certain value (about 20 mm here), which is obviously different from that in the multi-pass weldments and the selective laser melting (SLM) components. The restraint condition of the substrate can apparently affect the magnitude and distribution of longitudinal RS in the beam, while that almost has no influence on transverse RS in the beam. In terms of numerical results, the generation mechanism and distribution of RS in WAAM components have been systematically illuminated in the current work, which is quite useful to guide the mitigation of the generated high RS.
Aluminum‑silicon (AlSi) alloys of high silicon contents are composite materials; they are used whenever high casting properties are required. They are slightly ductile below 8wt%Si. An increase in ...ductility can be obtained by refining Si-crystals in elaboration or by a further hot working. In the present work, an Al-7wt%Si alloy was processed by Equal Channel Angular Extrusion (ECAE) at temperatures 20 °C and 160 °C up to three passes. The die was formed by two cylindrical channels with characteristic angles Φ = 110° and Ψ = 0. EBSD, X ray diffraction (XRD) and Strain Rate Sensitivity (SRS) were used to characterize the microstructure and the mechanical properties. High levels of strain were introduced at both temperatures. The activation volume was lowered to 125b3 and 210b3 at 20 °C and 160 °C respectively and was considered to be dislocation density dependent. The remaining dislocation densities calculated from EBSD, XRD and SRS experiments are quite different. This was explained by the scale difference and by the sensitivities of the methods to the free surface effect.
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•Casting Al-7wt%Si alloy was processed by ECAE at 20 °C and 160 °C.•The microstructure was highlighted by XRD and EBSD imaging.•SRS curves lead to an activation volume dislocation density dependent.•Dislocation density ρ was computed by SRS, XRD and KAM imaging.•The sensitivity of EBSD on surface effects leads to lower values of ρ.
Since friction stir welding tools fail in service under various mechanisms, it is difficult to mitigate tool failure based on mechanistic understanding alone. Here we use multiple machine learning ...algorithms and a mechanistic model to identify the causative variables responsible for tool failure. We analyze one hundred and fourteen sets of experimental data for three commonly used alloys to evaluate the hierarchy of causative variables for tool failure. Three decision tree based algorithms are used to rank the hierarchy of the relative influence of six important friction stir welding variables on tool failure. The maximum shear stress is found to be the most important causative variable for tool failure. This is consistent with the effect of shear stress on the load experienced by the tool. The second most important factor is the flow stress which affects the plasticized material flow around the tool pin. All other variables are found to be significantly less important. Three algorithms also generate identical results and predict tool failure with the highest accuracy of 98%. A combination of mechanistic model, machine learning and experimental data can prevent tool failure accurately.
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To investigate the impact of various forms of hole expansion strengthening of split mandrel (HESSM) process on the fatigue performance of 7050 aluminum alloy, a 3D finite element simulation analysis ...model is established for once hole expansion strengthening (OHES) and twice hole expansion strengthening. HESSM experiment is conducted to explore its influence on hole wall stress, microstructure, and fatigue life. The results show that the depth of the plastic deformation layer in the middle area of the hole wall is 1.69 times for specimens by twice hole expansion strengthening than that of OHES. Additionally, residual stress on the hole wall is higher and uniform for compared with OHES, when by twice hole expansion strengthening in opposite directions (THESOD) using split mandrel. The median fatigue life of the specimen by OHES is 1.52 times that of without expansion strengthening (WES). The median fatigue life of the specimen by twice hole expansion strengthening in the same direction using split mandrel is 1.73 times that of WES, and the median fatigue life of the specimen by THESOD using split mandrel is 1.80 times that of WES.
Self-lubricating polytetrafluoroethylene-containing PEO (PEO-PTFE) composite coatings were prepared by vacuum impregnation on plasma electrolytic oxidized aluminum alloy with different cathodic ...voltages. The topography, microstructure and composition of the composite coatings were investigated by FESEM equipped with EDX and XRD. The friction and wear properties were evaluated in the load range of 5–20 N using a reciprocating tribometer. The results show that the tribological properties of PEO-PTFE composite coatings are greatly influenced by the surface microstructure of PEO coating. The PEO coating fabricated at 150 V cathodic voltage shows coarser microstructure, while the corresponding PEO-PTFE composite coating registers superior self-lubricated property with lowest friction coefficient of 0.1 and 0.09 under the applied loads of 5 N and 10 N, respectively. In term of wear resistance ability, the 90 V composite coating possesses relatively low wear rate about 7.47 × 10−6 mm3·(N·m)−1 with the coefficient of 0.13 under the test load of 10 N. The increased microcracks and diameter of micropores, like “grooves” and “ridges” on PEO coating, is beneficial for providing the scope for low-lubricating PTFE material, which can form smooth lubricating film during the friction process.
•Self-lubricating PEO-PTFE coating was successfully prepared on aluminum alloy.•The cathodic voltages have great influence on the microstructure of the coatings.•The PEO-PTFE coating exhibits low coefficient of friction.•PTFE lubricating film formed on the worn surface during the friction process.
Herein, the investigations conducted in the area of aluminum (Al) matrix composites reinforced with carbon nanotubes (CNTs) are presented. The application of CNT reinforcement in Al alloys is driven ...by its exceptional chemical and mechanical properties. The critical issues in the processing techniques, challenges in the interfacial mechanisms between the Al matrix and CNTs, and strengthening effects due to the presence of reinforcements are reviewed. The mechanical properties of CNT/Al composites are found to be effectively enhanced with an addition of CNTs even at a small amount. The extent of strength improvements depends mainly on the dispersion of CNTs in the matrix and interfacial bonding between the matrix and CNTs. Limited theoretical modeling can predict the properties of CNT/Al composites to some extent, but without considering the detailed processing parameters. Based on the gaps identified here, future research directions are suggested, including the relationships between the processing parameters and micro‐ and nanostructures, and multiscale mechanical modeling and simulation, aiming to further understand the strengthening mechanisms and develop advanced CNT‐reinforced Al and other metal composites for critical engineering applications.
Recent advancements in processes have paved the way for fabricating advanced metal matrix composites (MMCs). Carbon nanotubes (CNTs), being one of the strongest known materials, are increasingly used as reinforcement in MMCs due to their exciting prospects in nanotechnology applications. Herein, insights into recent developments in the processing techniques, strengthening mechanisms, and mechanical behavior of CNT‐reinforced aluminum composites are provided.
•A protocol is proposed to characterize damage at the scale of the microstructure in Al-Si-Cu alloys under mechanical loading.•The role of Fe content on the damage mechanisms of Al–Si–Cu alloy is ...studied.•Digital image correlation measurement is used to observe strain build-up in the microstructure of Al-Si-Cu alloy during in-situ test.•Fractographic analysis is here performed to study the failure mode of hard inclusions.
In order to study the role of Fe content on the damage mechanisms of Al–Si–Cu alloy on a microstructural level, a Digital Image Correlation (DIC) method has been developed and performed on two Al–Si–Cu alloys: a high-Fe alloy (0.1wt.% Fe) and a low-Fe alloy (0.8wt.% Fe). Tensile tests on flat specimens have been performed, and a Questar long distance microscope has been used for the in-situ observation during tensile tests. The field measurements allow to identify and track the development and localization of deformation, and the fracture surfaces of the tensile specimens are analyzed using Scanning Electron Microscopy and Energy-Dispersive X-ray spectrometry (SEM-EDX) to identify the damage mechanisms. The results show that crack initiation occurs through the fracture of hard inclusions, i.e. Si particles, iron-intermetallics and Al2Cu particles in the high stress concentration region. Cracks often propagate through the fracture of hard inclusions rather than by their decohesion from the matrix.
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