Search

The efficiency of an engine material is closely correlated with its surface area. In order to investigate wear properties, effect of surface contact area as well as silicon addition at the eutectic level of Al-Cu-Mg alloy has been studied. This test is performed under room atmosphere and dry sliding conditions using a standard pin-on-disk apparatus. Weight reduction method is adopted to measure the wear rate in microns to get more accurate results. A load varying from of 5 to 50N and a constant sliding speed of 0.77ms-1 are maintained throughout the test. The test results show that a lower contact surface area has a negative impact on the wear properties having higher wear rate, while the coefficient of friction of the alloy and Si addition into the alloy improve the properties to some extent. Reduction of the contact surface area increases the unit pressure and decreased material volume causes softening of the alloy matrix, resulting in a higher wear rate and coefficient of friction. The Si addition offers such an improvement mostly for an increase in strength via the Si-rich intermetallic formation. A microstructural study confirms a lower abrasive wear with a minor plastic deformation on the worn surfaces of Si added alloy and wear with higher contact surface. The Si-added alloys contain the fine and strong Si-rich intermetallic, which are responsible for such a smooth worn surface. [ABSTRACT FROM AUTHOR]

The efficiency of an engine material is closely correlated with its surface area. In order to investigate wear properties, effect of surface contact area as well as silicon addition at the eutectic level of Al-Cu-Mg alloy has been studied. This test is performed under room atmosphere and dry sliding conditions using a standard pin-on-disk apparatus. Weight reduction method is adopted to measure the wear rate in microns to get more accurate results. A load varying from of 5 to 50 N and a constant sliding speed of 0.77 ms−1 are maintained throughout the test. The test results show that a lower contact surface area has a negative impact on the wear properties having higher wear rate, while the coefficient of friction of the alloy and Si addition into the alloy improve the properties to some extent. Reduction of the contact surface area increases the unit pressure and decreased material volume causes softening of the alloy matrix, resulting in a higher wear rate and coefficient of friction. The Si addition offers such an improvement mostly for an increase in strength via the Si-rich intermetallic formation. A microstructural study confirms a lower abrasive wear with a minor plastic deformation on the worn surfaces of Si added alloy and wear with higher contact surface. The Si-added alloys contain the fine and strong Si-rich intermetallic, which are responsible for such a smooth worn surface.

Cold expansion of fastener holes is a recognized technique for enhancing the fatigue life of holed plates utilized in detachable joints. This method involves introducing compressive residual stress around the holes, which has proven to be effective in improving the structural integrity and longevity of such components. In this research, the role of using different plasticity models in finite-element simulations of cold expansion (CE) in determining residual stress distribution and predicting the fatigue life of lap joints was investigated. Finite-element simulations were conducted to analyze the distribution of residual stress in cold-expanded Al-alloy 2024-T3 plates utilized in double-shear lap joints. Three time-independent plasticity models, specifically multilinear kinematic hardening, multilinear isotropic hardening (M.L.I.H) based on monotonic tensile tests, and nonlinear combined hardening models derived from saturated hysteresis stress and strain loops, were employed in the simulations. These models allowed for an accurate determination of the residual stress distribution in the plates. In finite-element simulations, two CE sizes of 1.5% and 4.7% were employed to create residual stresses. In the simulations, after creating residual stress by CE, remote sinusoidal loads are applied to the joints corresponding to the previously conducted fatigue tests in order to obtain stress and mechanical strain distributions. In order to predict the fatigue life, four different multiaxial fatigue criteria (Smith–Watson–Topper, Glinka, Kandil–Brown–Miller, and Fatemi–Socie) were employed, using the stress and strain distributions obtained from the finite element simulations with the different plasticity models. The simulations yielded varying stress and strain distribution results for the multilinear kinematic and M.L.I.H models, while the results of the nonlinear combined hardening model fell between the other two models. Notably, the fatigue life prediction based on the nonlinear combined hardening plasticity model closely matched the experimentally observed fatigue lives, with an absolute percentage deviation of 24.8%. [ABSTRACT FROM AUTHOR]

Aiming at the collapse deformation problem of ultra-wide Al-alloy intermediate slabs on the finishing mill run-in table during the hot rolling process, the collapse deformation prediction model of ultra-wide 7075 Al-alloy intermediate slabs based on particle swarm optimization and support vector regression (PSO-SVR) was proposed. The 7075 Aluminum alloy (Al-alloy) constitutive relationship in a temperature range of 330-370 °C was established by the Gleeble thermal compression experiment. According to the actual transporting process, the thermomechanical coupling finite element model (FEM) of 7075 Al-alloy intermediate slabs was established. It was demonstrated that width, temperature, and transportation time were positively related to contact length, while thickness was negatively related to contact length. The PSO-SVR collapse deformation prediction model was proposed by combining simulation data and the PSO-SVR algorithm. The PSO-SVR prediction model constructed was applied and verified by production test in the "1 + 3" hot rolling production line of an Al-alloy production line. The results show that the prediction model can achieve 100% prediction accuracy to predict whether the slab can be produced normally, and the maximum error of the contact length was 10.5%, it can provide guidance for the high-quality and stable production of ultra-wide Al-alloy. [ABSTRACT FROM AUTHOR]

Although the current field of application of Al–alloy 7075 (AA7075) is vast, it is still limited due to some drawbacks, especially due to its susceptibility to stress corrosion cracking (SCC). This work aims to evaluate the microstructural, mechanical, and stress corrosion cracking (SCC) behaviors on an AA7075 in flat format deformed by a combination of repetitive corrugation and straightening (RCS) and accumulative roll bonding (ARB) techniques. Four different deformation routes were applied, namely: ARB (A), RCS (R), RCS + ARB (RA) and ARB + RCS (AR). As expected, the efficiency for grain refinement depends on the applied route, in terms of average grain size regarding the initial condition IC): AR > A > RA > R. All conditions resulted in unimodal and widened grain size distributions of micro-, submicro- and nano-metric dimensions. The study of crystallographic orientations showed that route R did not generate any new texture, whereas different preferred orientations were obtained for routes A, RA, and AR. The hardness and three-point bending tests showed an improvement of mechanical strength in the following order: AR > RA > A > R. The cracks per cm2 obtained in the corrosion study indicated that the best SCC resistance was R > A > AR > RA. Based on the above, the best combination of microstructural, mechanical, and SCC properties until one deformation pass was obtained by the single route of the ARB process.

The effect of adding zirconium (Zr) as an alloying element to Al-Cu-Mg alloy on the hardness and corrosion of this alloy was investigated. The hardness and polarization test results of samples treated for various periods by aging at 423.15 K for 3hr showed a significant increment in the Brinell hardness (HBW) improvement ratio of 115.6% (from 45HBW to 97HBW) and an extreme reduction the corrosion rate of the alloy after Zr adding decrease in the current density by 79.42% (from 56.50 µA cm-2 to 11.63 µA cm-2) with aging for 3 hr compared to the base alloy. The impact of this addition is also reflected in the strengthening, recrystallization, and modification of the grain microstructure. These changes were clearly demonstrated by microscopic testing and proves that the addition of Zr has a considerable synergistic effect causing inhibition of recrystallization and refinement of grain size. [ABSTRACT FROM AUTHOR]

This study discussed the effect of the heterogeneous microstructure generated through the Repetitive Corrugation and Straightening (RCS) process on the mechanical and stress corrosion cracking behavior of the AA7075. As a result of the RCS process, significant grain refinement was obtained. The average grain size ranged from 126 to 59 μm, for the initial condition and 4 RCS passes, respectively. The yield strength and hardness increased 170% and 15% from the initial pass, remaining almost constant afterward. The evaluation of stress corrosion cracking showed a decrement in the number of cracks of 21.6% and 23.5% between the initial condition and fourth RCS passes. The cracking and pitting corrosion were the dominant mechanisms in the tested samples. The mechanical and corrosion results were also discussed in terms of the microstructural features.

Results are provided for a study of specimen microstructure and strength properties obtained by 3Dprinting (selective laser melting) of Al–Mg–Sc alloy also subjected to heat treatment. [ABSTRACT FROM AUTHOR]

Water uptake, adhesion and corrosion performance of silicone-epoxy coating on 2024 Al-alloy treated with different GLYMO were systematically studied by gravimetry, electrochemical measurements, DSC, pull-off adhesion and salt spray tests. The results showed that GLYMO not only enhanced the cross-linking of the silicon-epoxy coating but also enhanced the bonding between the coating and the Al-alloy interface. This gives the coating better wet adhesion, less water absorption and improves the corrosion resistance of the coating. The micro-nano silane layer, preferentially between the coating and Al-alloy oxide layer, was validated by the model of the water concentration jump. [ABSTRACT FROM AUTHOR]

Friction Stir Welding (FSW) is one of the modern and constantly evolving technologies of solid state joining and is used for welding a wide range of materials. The main parameters of friction stir welding such as rotational speed of the tool, movement speed and the angle of a tilt are analyzed in this article. 6XXX aluminium alloys have been investigated. The examined mechanical properties of the welds include hardness and strength, which are both important sources of information about quality of welding of the materials used in constructions.

To solve the problem of insufficient strength of thick aluminum alloy welded joints, this study introduces a pioneering technique known as variable-polarity plasma arc keyhole-tungsten inert gas cover hybrid welding (VPPA keyhole-TIG covering welding), which is designed for welding large-thickness aluminum alloys without any weld groove. Using 13-mm-thick 2319 aluminum alloy plates as experimental materials, plasma arc butt welding experiments were conducted by varying the plasma gas flow rate and application of cover welding. The research findings underscored that the use of cover welding, coupled with an increase in the plasma gas flow rate, markedly improved the overall performance of the weld. An average tensile strength of 299.0±4.0 MPa and an elongation rate of 4.5±0.3 % were achieved for the welded joint. A microscopic analysis revealed that the heightened plasma gas flow rate did not precipitate the θ' phase but instead resulted in undesired grain size enlargement, leading to reduced joint hardness. The secondary thermal cycle effect of covering welding played a pivotal role in facilitating the nucleation of needle-like θ' strengthening phases within the matrix, ranging in size from 50 to 150 nm. This phenomenon has emerged as a principal factor contributing to the substantial enhancement of the mechanical properties of welded joints. [Display omitted] • Introduced an advanced welding process designed to enhance the properties of joint in thick Al-alloy plate. • Revealed the reinforcement mechanism on the weld's properties through the analysis of the microstructure of the joints. • Summarized the microstructure evolution of the joints under the influence of plasma gas flow rate and cover pass welding. [ABSTRACT FROM AUTHOR]

The micro and nano drilling holes are produced by a Q-switched Nd :YAG laser (1064 nm) interaction with 8009 Al alloy using two kinds of nanoparticles. Nanoparticles are tungsten carbide (WC) and silica carbide (SiC). The micro and nano holes have been investigated with different laser pulse energies (600, 700 and 800)mJ, different repetition rates (5Hz and 10Hz) and different concentrations of nanoparticles (90%, 50% and 5% ). The results indicate that micro and nano holes have been achieved under conditions of 600 mJ laser pulse energy, 5Hz laser repetition rate, and 5% concentration of the nanoparticles (for the two types of nanoparticles). The diameters of holes are increase to millimetres and cracks are formed with increasing of the laser pulse energy, laser repetition rate and high concentration of nanofluid. [ABSTRACT FROM AUTHOR]

Metal matrix composites consisting of Al-alloy as matrix and B4C particles as ceramic reinforcement are widely used for numerous advanced applications requiring high strength, hardness, wear resistance, good thermal properties, neutron radiation shielding characteristics, etc. Among the processing routes for such composites, the liquid metallurgy route possesses the advantages of being cost-effective and capable of manufacturing bulk composites. Numerous efforts were made so far to employ different Al-alloys and a wide range of processing parameters for fabricating such composites via casting route. These studies display a considerable variation in the composites' final mechanical properties and therefore warrants proper selection of the processing parameters to target for the desired applications. Within the scope of this work, the vast literature available on cast Al-B4C composites has been systematically reviewed to critically analyze the influence of the various processing parameters on different relevant mechanical properties. Based on the thorough analysis, the combinations of processing parameters that yield optimum mechanical performance in the case of some selected Al-alloy-based composites have been identified. The inferences drawn in this work will immensely facilitate the selection of process parameters for the development of future particle-reinforced cast Al-B4C composites. [ABSTRACT FROM AUTHOR]

In this paper, fatigue crack growth of edge crack in 2024 T351 aluminum alloy plate repaired with bonded composite patch under constant and variable amplitude loading (VAL) was predicted. The Al-alloy plate was repaired with symmetric patch �Boron/Epoxy�. Additionally to constant amplitude loading (CAL), the effects of single overload and band overload were investigated for repaired and unrepaired Al-alloy plates. The obtained results confirm the improvement in repair performances by composite patch on fatigue lives and crack growth rates for all applied cycles (CAL and VAL) compared to unrepaired plates. A retardation effect was observed in application of single overload compared to band overload with the same stress ratio (R=0.2) for unpatched plate and characterized by instantaneous delays. However, this retardation effect is increased by the presence of the patch repair which leads to the higher fatigue life. Retardation effect was neglected for lower overload ratio (ORL>1.8). Comparison in fatigue life and crack growth rates under the same overload ratio (ORL=2.4) between repaired and unrepaired plates show the supplementary beneficial effects in combination of overloading and patch repair

The T-joints of medium-thick 6082 Al-alloy plates created by dual pulsed gas metal arc welding (P-GMAW) and bilateral synchronous welding were investigated to improve weld quality using the adaptive deposition method, which calculates the minimum amount of deposition according to the welding condition, groove size, and cross-sectional area, effectively reducing the heat input and deformation of the welds on the basis of weld filling. The optimized linear energy with a wire feed speed (WFS) of 9.5 m/min can ensure a well-formed weld with a complete root fusion, and high-quality T-joint welds were obtained both in root openings of 0 mm and 1 mm. The biggest penetration was 4 mm, which was four times more than that of the result from a single torch welding process. When the distance between the two welding torches exceeded 20 mm, the molten pool was completely separated, and process pores were observed in the unfused root zone. Influenced by the thermal cycles in asymmetric welding, the hardness distribution changed: the width of the softer zone at the base plate with the fore arc was smaller than that zone with the rear arc. Furthermore, dual P-GMAW bilateral synchronous welding with an asymmetric heat source can further reduce the deformation of the welded joint by about 20% compared to that of symmetric welding.

Al-alloys possess a very good combination of mechanical properties such as lightweight, good corrosion performance, good formability and high strength. Thus, they are widely employed in several industries, particularly in transport industry, where lightweight is required. However, fusion joining of these alloys, particularly age hardened grades such as AA7075-T6, involve several difficulties such as porosity formation, cracking and loss of strength in the weld area. Thus, successful joining of these alloys will further increase their use in industrial applications. In this respect, solid state joining or fusion welding techniques with low heat input such as cold metal transfer (CMT) gas metal arc welding (GMAW) technique or laser beam welding are promising joining methods. This study aims at investigating the formation of weld defects (i.e., pores) and determining the effect of pores on mechanical performance of the AA7075-T6 plate joints produced using CMT arc welding technique. For this purpose, AA7075-T6 Al-alloy plates with a thickness of 2 mm were joined using both conventional CMT and CMT pulse arc welding techniques. The microstructural and mechanical properties of the welded plates were investigated by detailed optical microscopy investigations, micro-hardness measurements and tensile tests. Moreover, a correlation between the joint performance and the formation of porosity in the fusion zone (FZ) was also attempted to show the effect of the presence of large pores on the mechanical behavior of the joint. [ABSTRACT FROM AUTHOR]

The mechanical behavior and microstructural evolution of an AA2017 aluminum alloy processed by ECAP with an equivalent simple shear deformation of ∼ 6 at 200 °C were studied. Samples were characterized by means of scanning electron microscopy (SEM-EDS- EBSD), image-assisted by focus ion beam (FIB), Vickers microhardness and X-ray diffraction (XRD) techniques. During the deformation process, the Al 2 Cu precipitates did not get fragmented or re-absorbed in the Al matrix. After the first ECAP pass, at least 50% of grains displayed an ultrafine size. The EBSD analysis showed an increment of the misorientation angle immediately after the first ECAP pass. The macrotexture evolution was explained in terms of the formation of f1: A 1θ ∗, A θ , Ā θ , A 2θ ∗, f2: C θ , B ¯ θ , B θ , Ā θ , A θ , A 1θ ∗ and f3: C θ , B θ , B ¯ θ , A θ , Ā θ , A 2θ ∗ fibers. The macro-residual stress measurements of the highly deformed samples showed linear sin2ψ profiles. The micro and macro-residual stresses were compatible with dislocation rearrangement, in which the annihilation and formation were in quasi-equilibrium. It was found that the highest microhardness value (1176 MPa) and grain refinement (at least 20% of grains showed a size smaller than 100 μm2) appeared after the first extrusion pass. The decrease in hardness, after the second pass and the residual stress stability, could be associated to a dynamic recovery phenomenon. • The micro-strain increased considerably between the first and the sixth ECAP passes. • Dynamic recovery occurred after the first extrusion pass. • Texture and residual stress explained in terms of shear stress phenomenon. • Hardening mechanism described related to grain refinement and dislocation density. [ABSTRACT FROM AUTHOR]

The use of Al-alloys is increasing in the automotive industry due to the pressing necessity to reduce weight and fuel consumption. Several parts concerning the car body are assembled through welding, where a high-quality seam is a key requirement. For this purpose, laser welding stands as an appealing option. On the other hand, laser welding of Al-alloys is a complex process due to the high reflectivity, reactivity, and crack susceptibility of these materials. In many cases, such issues limit the applicability of the autogeneous welding, which is an advantageous feature of laser welding. High-brilliance fiber lasers have been an enabling technology for improving the weldability of Al-alloys. However, laser welding of Al-alloys, especially in a lap-joint configuration, requires robust processing conditions able to maintain seam quality for each weld in high volumes even with part tolerances and tooling variability. Accordingly, this work discusses the process development and monitoring in laser welding of 5754 Al-alloy. In particular, the process was carried out in a double lap-joint configuration with 1 mm sheets, commonly used in automotive applications. A 3 kW fiber laser with in-source integrated monitoring capability was employed as the light source. The process feasibility zone was investigated as a function of laser power and welding speed, while the effect of focal position was investigated for the weld robustness. Weld seam types and defects were identified, as well as the monitoring signals associated light back-reflected from the process. [ABSTRACT FROM AUTHOR]

Precipitation kinetics and mechanisms within an Al-Mn-Be-Cu quasicrystal strengthened alloy at 300°C were studied using in-situ transmission electron microscopy. The alloy was cast into a copper mould. Quasicrystalline precipitates formed throughout the Al-rich solid solution, whilst heterogeneous formations of Al2Cu and T-phase occurred on icosahedral quasicrystalline particles formed during solidification. The formation of quasicrystalline particles and T-phase was limited by manganese diffusivity, whilst that of Al2Cu by copper diffusivity. The precipitation produced only a small hardening effect.

Aluminum alloy is the important alloy which has been widely used. To reduce waste, it is necessary to thixoform these alloys in near net shape. Semi-solid slurry is the key in process. In this work, the semi-solid slurry of ZL101 aluminum alloy was prepared by using serpentine channel. Effect of process parameters on the microstructure of semi-solid ZL101 aluminum alloy produced by serpentine channel was investigated. The results show that, the morphology of primary α-Al grains transformed from rosette to spheroid with decreasing pouring temperature. Satisfied semi-solid slurry of ZL101 aluminum alloy was prepared with pouring at 630°C to 670°C. Increasing curve number can improve the morphology of primary α-Al grain and decrease grain size with same pouring temperature. Desired slurry can be obtained with the lower pouring temperature when serpentine channel is preheated. It can make the primary nucleus gradually evolve into spherical and near-spherical grains with the effect of “self-stirring” in serpentine channel and chilling.

The repetitive corrugation and straightening process is a severe plastic deformation technique that is particularly suited to process metallic sheets. With this technique, it is possible to develop nano/ultrafine-grained structured materials, and therefore, to improve some mechanical properties such as the yield strength, ultimate tensile strength, and fatigue lifetime. In this study, an Al-6061 alloy was subjected to the repetitive corrugation and straightening process. A new corrugation die design was proposed in order to promote a heterogeneous deformation into the metallic sheet. The evolution of the mechanical properties and microstructure obtained by electron backscatter diffraction of the alloy showed a heterogeneous distribution in the grain size at the initial cycles of the repetitive corrugation and straightening process. Uniaxial tensile tests showed a significant increase in yield strength as the number of repetitive corrugation and straightening passes increased. The distribution of the plastic deformation was correlated with the hardness distribution on the surface. The hardness distribution map matched well with the heterogeneous distribution of the plastic deformation obtained by finite element simulation. A maximum average hardness (147 HV) and yield strength (385 MPa) was obtained for two repetitive corrugation and straightening cycles sample.

Abstract The present paper considers the problem of the low-temperature deposition of the hard coatings on the alloys having a low melting point and a high affinity for oxygen, like aluminum or magnesium alloys. It is demonstrated that a hard ZrN coating can be produced on the 2024 aluminum alloy by the low-temperature vacuum-arc deposition method. To achieve high adhesion strength between the coating and substrate, the substrate was sputtered by low-energy inert Ar+ ions before the deposition process in order to remove the natural oxide layer. The optimal technological regimes selected and used allowed obtaining the stoichiometric ZrN coating of extremely low roughness (0.061 μm), uniform thickness (~1 μm) with nano-scale columnar microstructure with the cross-sectional size of the columnar grains of ~20–50 nm. The layered microstructure of the obtained coating respectively consisted of the columnar and V-shaped grains in the lower and upper layers comes to be in the 'transition zone' on the 'structure-zone diagram'. The lower layers consist of a number of Al x Zr y phases along with the Zr 3 N 4 orthorhombic phase, while the outmost layer of the film contains the single ZrN fcc phase. In comparison with the substrate alloy, the produced ZrN coating is shown to possess the superior anti-corrosion properties in saline solution, a high hardness (~20 GPa) and elastic modulus (196 GPa), high adhesion strength both at the progressively increased load and at cyclic dry sliding of the conical diamond indenter with the 50 μm tip, low friction coefficients and high wear resistance at the reciprocating sliding both in the dry and wet (liquid paraffin) conditions against the conical diamond indenter with the 50 μm tip and 8 mm Si 3 N 4 ball, respectively. Highlights • Method of low-temperature arc deposition of hard coatings on the low melting point alloys • Preliminary sputtering by low-energy inert Ar+ ions for removing the natural oxide and achieving high coating/substrate adhesion • Vacuum arc deposited ZrN coating of 1 μm thick with nano-scale (20–50 nm) columnar microstructure • The ZrN coating of high hardness (~20 GPa) and wear resistance, and low friction and corrosion rate [ABSTRACT FROM AUTHOR]

Al-alloys are the most widely used sheet material in the world after steel because of their exceptional properties. Al-alloy sheets are used for producing structural parts of aircrafts and automobile components. This paper presents the optimization of dimensional accuracy of kerf geometry during pulsed Nd:YAG laser cutting of thin Al-alloy sheet. Top kerf width, bottom kerf width and top kerf deviation are considered as quality characteristics for laser cut kerf. These laser cut quality characteristics are the functions of four laser cutting parameters namely O2 gas pressure, pulse width, pulse frequency and cutting speed. Experimental results of these characteristics have been obtained by performing the experiments using L9 orthogonal array (OA) and these results are optimized simultaneously using Grey relational analysis (GRA) coupled with fuzzy logic (FL). Subsequently, the significance of laser cutting parameters for the process has been found by employing the analysis of variance (ANOVA). From the results, pulse frequency is found as the most contributing (48.40%) laser cutting parameter for the study. [ABSTRACT FROM AUTHOR]

Aluminum and its alloys are widely used in our daily life because of their desirable physical properties. Improving the quality of Al-alloys surface layers is required for industrial applications. Nd: YAG pulsed Nanosecond Laser was used in irradiating aluminum 1100 alloy to study the surface morphology and hardness properties. Scanning Electron Microscope (SEM) images reveal the presence of small holes with different diameters that are produced by the irradiation of Aluminum alloy surfaces with different laser power densities. The diameters of the produced holes are decreased gradually by increasing the laser power density. Minimum diameter of about 1.84m is obtained after irradiating the aluminum surface with 1256.04MW/cm2 at which semi-periodic holes-like pattern were produced. An increase in the Vickers microhardness values was obtained until the maximum value of 28 HV was reached at laser power density of 750.16MW/cm2. After reaching the maximum value, a fast decrease in the microhardness values was observed. Such changes in microhardness values maybe attributed to the lattice disorder and the change in the defect density produced by laser irradiation. [ABSTRACT FROM AUTHOR]

In this paper, fatigue crack growth of edge crack in 2024 T351 aluminum alloy plate repaired with bonded composite patch under constant and variable amplitude loading (VAL) was predicted. The Al-alloy plate was repaired with symmetric patch “Boron/Epoxy”. Additionally to constant amplitude loading (CAL), the effects of single overload and band overload were investigated for repaired and unrepaired Al-alloy plates. The obtained results confirm the improvement in repair performances by composite patch on fatigue lives and crack growth rates for all applied cycles (CAL and VAL) compared to unrepaired plates. A retardation effect was observed in application of single overload compared to band overload with the same stress ratio (R=0.2) for unpatched plate and characterized by instantaneous delays. However, this retardation effect is increased by the presence of the patch repair which leads to the higher fatigue life. Retardation effect was neglected for lower overload ratio (ORL>1.8). Comparison in fatigue life and crack growth rates under the same overload ratio (ORL=2.4) between repaired and unrepaired plates show the supplementary beneficial effects in combination of overloading and patch repair

In this paper, fatigue crack growth of edge crack in 2024 T351 aluminum alloy plate repaired with bonded composite patch under constant and variable amplitude loading (VAL) was predicted. The Al-alloy plate was repaired with symmetric patch "Boron/Epoxy". Additionally to constant amplitude loading (CAL), the effects of single overload and band overload were investigated for repaired and unrepaired Al-alloy plates. The obtained results confirm the improvement in repair performances by composite patch on fatigue lives and crack growth rates for all applied cycles (CAL and VAL) compared to unrepaired plates. A retardation effect was observed in application of single overload compared to band overload with the same stress ratio (R=0.2) for unpatched plate and characterized by instantaneous delays. However, this retardation effect is increased by the presence of the patch repair which leads to the higher fatigue life. Retardation effect was neglected for lower overload ratio (ORL>1.8). Comparison in fatigue life and crack growth rates under the same overload ratio (ORL=2.4) between repaired and unrepaired plates show the supplementary beneficial effects in combination of overloading and patch repair [ABSTRACT FROM AUTHOR]

The dissolution of aluminum alloy AA2050-T3 (which contains 0.77 wt.% Li) during a chemical pretreatment sequence was investigated. Atomic emission spectroelectrochemistry (AESEC) was used to quantitatively measure the dissolution rates of individual alloying elements during a complete pretreatment sequence. The results reveal significant Li and Al dissolution, and Cu enrichment during NaOH exposure. When the alloy was exposed to HNO 3 , excess Cu was preferentially dissolved in addition to the dissolution of Fe, Mn and Mg. Polarization testing in conjunction with on-line AESEC reveal a decrease in both anodic and cathodic currents, along with an increase in the alloy pitting potential, following pretreatment. In addition, what appears to be a protective Li/Al surface film was also determined to exist with GDOES surface profiles following polarization as indicated by an increase in the surface Li/Al ratio and which favors the formation of insoluble Al species during anodic polarization in neutral electrolyte and strongly suggests a stabilizing effect of Li on the Al passive film. Beyond the context of surface pretreatment, which is necessary precursor to conversion coating, the study herein also provides significant insights into the corrosion of AA2050-T3 − including selective dissolution and its attendant rate − which are previously unreported. [ABSTRACT FROM AUTHOR]

An Al-Zn-Mg-Cu alloy with high zinc content was successfully produced by selective laser melting (SLM). A small amount of discontinuous η particles precipitates into the inter-dendritic areas, which is less than in the corresponding cast sample. After T6 heat treatment, almost all η particles dissolve in the Al-matrix. The hardness of the as-synthesized SLM material is 133 ± 6 HV 0.05 , similar to the homogenized cast sample, and it increases to 219 ± 4 HV 0.05 after the T6 heat treatment. This value is higher than for the corresponding T6 cast sample, which indicates that SLM processing leads to a material with improved mechanical behavior. [ABSTRACT FROM AUTHOR]

In this study the effect of the cooling rate on the microstructure of Al94Mn2Be2Cu2 alloy was investigated. The vacuum induction melted and cast alloy was exposed to different cooling rates. The slowest cooling rate was achieved by the DSC (10 K•min-1), the moderate cooling rate succeeded by casting in the copper mould (≈1 000 K•s-1) and the rapid solidification was performed by melt spinning (up to 106 K•s-1). The microstructure of the DSC-sample consisted of α-Al matrix, and several intermetallics: τ1-Al29Mn6Cu4, Al4Mn, θ-Al2Cu and Be4Al(Mn,Cu). The microstructures of the alloy at moderate and rapid cooling consisted of the α-Al matrix, i-phase and θ-Al2Cu. Particles of i-phase and θ-Al2Cu were much smaller and more uniformly distributed in melt-spun ribbons.

Generally failures of different aircraft components and parts are revealed and examined by the use of non-destructive examination methods. In further detailed explanation and interpretation of failures optical and scanning electron microscopy are used. This paper deals with a problem of a crack on aircraft wheel rim made from aluminium alloy 2014-T6.The crack was observed during regular control by the maintenance unit for non-destructive examination of the Slovenian air carrier Adria Airways. The crack on the rim of an aircraft wheel investigated was a typical fatigue crack. At same time a numerous pits were found which served as stress concentrations on the rim surface.

Electron backscatter diffraction (EBSD) and scanning electron microscopy were combined to study the effect of residual defect density on corrosion initiation in aluminium alloy AA2024-T3. EBSD was used to determine the level of misorientation (MO), from pixel to pixel, within individual grains. TheMO can be determined with respect to either the average orientation angle of the grain orwith respect to the average orientation angle of the surrounding pixels (in this instance, amatrix of 7 ×7 surrounding pixels has been applied). Herein, the MO, determined using the surrounding pixels, was used as the means for the assessing the level of defect density within a grain. Itwas found that there was a noteworthy, but not definitive, correlation ofMOwith corrosion initiation after 1 min exposure to 0.1MNaCl solution. Additionally, the S and θ-phase particles were also identified using EBSD, displaying a range of MO and therefore defect density. [ABSTRACT FROM AUTHOR]

In-situ electron microscopy is an emerging technique for real time visualisation of micro-structural changes of a specimen under some applied constraints inside microscope. In this study, in-situ nanoindentation experimentation on a carbon nanocoil inside transmission electron microscope has been reported. The elastic modulus of the carbon nanocoil is found to be 177 GPa. Similar experiments are also carried out on carbon nanotubes, but force response of carbon nanotubes is beyond the limit of sensors presently available. The in-situ dissolution behaviour of the secondary phases of a 7xxx series aluminum alloy under high vacuum condition in scanning electron microscope (SEM) in the temperature range of 350 °C to 400 °C has been reported. We report for the first time using in-situ SEM technique that dissolution of the MgZn2-base phase present as eutectic and divorced eutectic forms could start at a temperature as low as 300 °C, although the usual homogenisation temperature of such alloys is always > 450 °C. Furthermore, the kinetics of dissolution of such phases, particularly when present in fine eutectic phase mixture, is significantly faster than what is observed under atmospheric pressure. It has been found that modification of surface composition under high vacuum condition plays a key role in the low temperature dissolution processes. It has further been found that the dissolution process does not start with the thinning of the inter-dendritic channels phase as proposed for Al-Zn-Mg-Cu alloys, rather it occurs by a combination of 'spheroidisation' and thinning process called 'the thinning, discontinuation, and full dissolution' mechanism. Results of the in-stu experiments under high vacuum are compared with the ex-situ dissolution experiments under normal atmospheric pressure. [ABSTRACT FROM AUTHOR]

The electrical resistively and intensity of X-ray diffraction reflexes were determined for overhead line wires deformed plastically and immersed at different solutions. Immersing (chemical ageing) was performed by plastic deformation along the wire axis. During chemical ageing the samples were exposed to the action of the Cl-, SO4 2-, and SO3 2- ions. Resistively was measured at room temperature and at liquid nitrogen temperature. After the X-ray and resistively measurement data were compared, it was found that three processes could take place: the flow of ions through the boundary between a sample and environment; the mechanical relaxation of vacancies near a line of dislocations, and the ordering of microstructure. These effects can lead to the anisotropy of resistively.