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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 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]

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]

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 work, an Al–Mn–Be–Cu alloy was studied containing a primary and eutectic icosahedral quasicrystalline phase in the as-cast microstructure. Special attention was given to a transmission electron microscopy investigation of precipitates formed within the aluminium solid solution (Al ss ) at different temperatures. At 200 °C, only binary Al–Cu precipitates (θ′) were formed. At 300 °C, icosahedral quasicrystalline (IQC) precipitates prevailed with a crystallographic orientation relationship with the Al ss. The rods of the T-phase (Al 20 Mn 3 Cu 2 ) which were precipitated above 400 °C, also had a specific orientation relationship with the Al ss . The primary and eutectic IQC microstructural constituent started to transform rapidly to the T-phase and Be 4 Al(Mn,Cu) at 500 °C. [ABSTRACT FROM AUTHOR]

The 6061 Al alloy in its T6 conditions is often considered a good candidate for applications requiring a good balance between strength and thermal conductivity. However, this alloy is often very difficult to process using laser powder bed fusion (PBF-LB) because of the development of hot cracks during fabrication. Here, we show that adding 2.3 wt% of Zr to the 6061 heritage alloy makes it processable by PBF-LB (suppression of hot cracks). Hot crack mitigation is attributed to grain refinement. However, the addition of 2.3 wt% of Zr greatly affects the microstructure and thus the mechanical and electrical/thermal properties of the Zr-modified 6061 alloy. Consequently, there is a need to design heat treatments to achieve a trade-off between yield strength and thermal conductivity. In this work, we designed two heat treatment sequences aiming at achieving such a trade-off: an adapted T6 sequence (550 °C/30 min + 180 °C/4 h) and direct ageing at 400 °C/4 h. On the basis of a multiscale microstructural study using optical microscopy, X-ray diffraction, and electron microscopy, we clarify the evolution of the microstructure induced by the designed heat treatments. The mechanical properties (hardness, tensile behavior) and thermal conductivity derived from electrical conductivity measurements are then discussed in light of the microstructural evolutions. The as-fabricated Zr-modified 6061 alloy shows a higher yield strength (370 MPa) than the heritage 6061 alloy in its T6 condition (260 MPa) but its thermal conductivity is found to be much lower (98 vs. 173 W/m.K). The two heat treatment sequences designed in this work enable the mechanical properties of the heritage 6061 alloy to be outperformed (yield strength of 350 and 460 MPa for the T6 and direct ageing heat treatment respectively) while maintaining an acceptable level of thermal conductivity (150 and 170 W/m.K for the T6 and direct ageing heat treatment respectively). [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The microstructure of an Al–Mn–Be–Cu alloy was characterised after melt spinning and heat-treatment at different temperatures. The optimised melt-spinning parameters made it possible to obtain ribbons with thicknesses ranging from 30 to 200μm, having a microstructure composed of a supersaturated Al-rich solid solution, finely dispersed icosahedral quasicrystalline (IQC) particles, and a small fraction of Al2Cu. The finest dispersion of the IQC-particles, and consequently the highest microhardness, was obtained on the wheel-side. The initial microstructure started to decompose at temperatures around 400°C. The IQC-phase was replaced by the intermetallic compounds τ1-Al29Mn6Cu4 and Be4Al(Mn,Cu). The maximum hardness of the ribbons, which was approximately 50% higher than in the as-cast state, was attained after heat treatment at 400°C, and could be attributed to the fine dispersion of τ1-Al29Mn6Cu4 and IQC-particles. [Copyright &y& Elsevier]

Abstract: For extrusion of hollow profile with asymmetric cross-section, existing FEM software cannot simulate the influence of divergent and welding on the metal flowing behaviors, because it is inability to deal with meshes separation and penetration during welding. A mesh-reconstruction technology based on the reverse engineering is proposed in this paper, and extrusions of Al-alloy hollow profiles with various cross-sections are simulated. The results show that the mesh-reconstruction technology can solve the problem of simulation termination caused by the meshes separation and penetration during porthole die extrusion. It is effective to analyze the metal flowing behaviors, temperature distribution, hydrostatic stress in weld-chamber, and stress on dies, which provides a practicable way for die structure design and optimization of porthole extrusion as well as quality forecast of extrusion products. [Copyright &y& Elsevier]

Abstract: The corrosion product activities of 24Na and 27Mg have been experimentally measured as a function of the MNSR reactor operation time. The 24Na corrosion product contribution is much more than the Mg activity in the MNSR reactor coolant and its activity increased with the reactor operation time. The activity of the 27Mg corrosion product reaches its saturation state in about 2h after the start of the MNSR reactor operation. The mean neutron flux and cross sections for the interactions of 27Al with neutrons in the MNSR reactor have been numerically calculated using MCNP-4C code. A simple mathematical model for the simulation of the coolant activation due to the corrosion products in the MNSR reactor has been proposed. This model has been based on considering the balance between the rate of radioactive nuclei production and their radioactive decays. The calculated 24Na and 27Mg corrosion products activities values are in a good agreement with the corresponding experimental measured values. [Copyright &y& Elsevier]

Abstract: The corrosion behaviour of Al-5Zn-0.02In-1Mg-0.05Ti-0.5Ce (wt.%) alloy has been investigated by immersion test, scanning electron microscopy, energy dispersive X-ray detector, electrochemical impedance spectroscopy and electrochemical noise. The results show that there exist different corrosion types of the alloy in 3.5% NaCl solution with the immersion time. At the initial stage of immersion, pitting due to the precipitates predominates the corrosion with a typical inductive loop at low frequencies in electrochemical impedance spectroscopy. The major precipitates of the alloy are MgZn2 and Al2CeZn2 particles. The corrosion potentials of the bulk MgZn2 and Al2CeZn2 alloys are negative with respect to that of α-Al, so the MgZn2 and Al2CeZn2 precipitates can act as activation centre and cause the pitting. In the late corrosion, a relative uniform corrosion predominates the corrosion process controlled by the dissolution/precipitation of the In ions and characterized by a capacitive loop at medium-high frequencies in electrochemical impedance spectroscopy. The potential noise of the pitting shows larger amplitude fluctuation and lower frequency, but the potential noise of the uniform corrosion occurs with smaller amplitude fluctuation and higher frequency. [Copyright &y& Elsevier]

Abstract: The deformation behavior of 7010 Al-alloy at elevated temperature was investigated. The specimens were solution treated at 723K for 2h and then water quenched to obtain the supersaturated solid solution (SSS). Tension tests of the SSS specimens were then conducted at temperatures of 623, 673, and 723K at various strain rates in the range 5×10−5 to 2×10−2 s−1. Stress dependence of the strain rate revealed a stress exponent, n of ∼8 throughout the ranges of temperatures and strain rates used. This stress exponent is higher than what is normally observed in Al–Zn alloys under similar experimental conditions. This high value of the stress exponent implies the presence of the threshold stress. This behavior resulted from a dislocation interaction with second phase particles due to precipitation at testing temperatures. The values of the threshold stress were observed to decrease exponentially with temperature. The presence of the threshold stress resulted in high apparent activation energy (∼180kJ/mol). The true activation energy was obtained by incorporating the threshold stress in the analysis. The normalized constitutive equation was then developed for the alloy under the present experimental conditions. [Copyright &y& Elsevier]

Abstract: The methods to study the “rheological behavior” of semi-solid metal, SSM, slurries are all based on measuring the viscosity. The viscosity is an indication of SSM capability in filling the mould and determines the required force for its deformation and flow. One way to measure viscosity is the application of parallel plate compression viscometery. A new “parallel plate compression machine” for commercial scale is designed, fabricated and tested for viscosity measurement. It is based on monitoring and registering the height changes of the test piece with time. The registered data is treated mathematically to plot strain–time graph from which the viscosity is calculated. The machine is capable of differentiating amongst various SSM microstructures ranging from dendritic to rosette and globular morphologies of the primary phase. [Copyright &y& Elsevier]

DLC films can play an important role in tribological properties of Al-alloys. A gradient layer of AlN/Ti/TiN/DLC film has been prepared by plasma-based ion implanted N, followed by Ti, and N and Ti, and finally C on 2024 Al-alloy. Emphasis has been placed on the tribological properties of the gradient layer. Its composition depth profile and chemical structure were characterized using X-ray photoelectron spectroscopy (XPS), the surface C-layer and the wear tracks were analyzed by laser Raman spectroscopy. The morphologies of the C-layer were observed by atomic force microscopy (AFM), the hardness of the gradient layer was measured with the mechanical property microprobe and the dry wear tests against AISI steel ball at different sliding loads were performed with a ball-on-disk wear tester in ambient environment. The results indicate that the gradient layer shows a gradual change in hardness, compact surface appearance and good tribological properties owing to the gradient structure. As the number of the sliding cycles or the load is increasing, the tribological properties decrease due to the graphitization of the DLC films. Meanwhile, the gradient layer can be controlled by PBII processing parameters, thus an optimized gradient layer can be obtained to offer the possibility of making aluminum alloys and other soft alloys qualified candidates for particular engineering applications. [Copyright &y& Elsevier]

Present investigation concerns development of AlSiMg–SiC composite microstructure with trace addition of scandium in the form of master alloy powder utilizing mechanical alloying technique. Influence of Sc on the phase formation in the present alloy has been demonstrated by carrying out differential scanning calorimetry (DSC) of the ball milled and solution treated samples. Variation of Vickers hardness of the samples as a function of ageing time shows that presence of SiC and Sc may reasonably improve the mechanical properties of the age hardened alloy. Scanning electron micrographs (SEM) and transmission electron micrograph (TEM) of the bulk samples demonstrate the influence of ball milling on the morphology and distribution of the SiC particulates and the precipitate. The formation of V-phase as a stable precipitate during ageing has been identified and characterized by carrying out the selected area diffraction pattern (SADP) analysis. [Copyright &y& Elsevier]

The addition of Sc and Zr into an Al–Mg–Mn alloy produced by selective laser melting exhibited exceptional properties. Multiple factors eventually lead to the improvement of properties, such as densification behaviors, grain characteristics, texture and the precipitated phases. We firstly investigate evolution of the melt pool characteristics which are varied under different processing parameters and lead to different solidified microstructures, densification behaviors and corresponding mechanical properties. Meanwhile, the characteristics of melt pool can be predicted through the normalized enthalpy of input energy, which presents more credible relationship with the melt pool dimensions. To this end, the relative density is up to 99.88% when the volume energy density and normalized enthalpy are combined used. Recrystallisation inhabitations induced by the added Sc and Zr is supposed after comparing the grain sizes under different conditions. Regrettably, the relationship between melt pool characteristics and the equiaxed/columnar ratio can not be described accurately, which due to the pseudo-equiaxed regions in XZ/YZ sections through regulating the melt track orientations via 67° scanning rotation. There are dispersed Al 6 Mn and Al 3 (Sc, Zr) particles exist in as-fabricated samples result in better mechanical properties and the subsequent aging treatment can further improve the comprehensive mechanical properties. Finally, the ultimate tensile strength and ductility is separately about 494.32 ± 4.16 MPa and 15 ± 1.27% after aging for 4 h at 325 °C. In contrast, the processing parameters have little impact on mechanical properties, especially for the yield strength, mainly owing to the homologous precipitate phase and grain sizes when the relative density is similar. The connection involving the whole periods from solidification to the final mechanical properties is discussed that may offer feasible ideas for alloy design and corresponding parameter optimization. [ABSTRACT FROM AUTHOR]

Abstract: The local structures around nickel and cobalt atoms in Al86Ni8Y6 and Al86Ni6Co2Y4.5La1.5 bulk amorphous alloys were measured by X-ray absorption spectroscopy. Strong bond-shortening and a concomitant reduction of nearest neighbours of Ni and Co were observed. The local structure around Ni is the same as that around Co which is attributed to site substitution of Ni by Co atoms in the amorphous structure. The configurational entropy is estimated to be the main thermodynamic driving force for the increase in glass forming ability when substituting Ni by Co and Y by La. The cluster-line model is not supported by our results. [Copyright &y& Elsevier]