Metals and Materials International最新文献

Underwater friction stir welding (UwFSW) of dissimilar brass (CuZn40) and aluminum (AA1100-O) joints have a more pronounced effect on the microstructure and crystallographic texture evolution than classical open-air friction stir welding (C-AFSW). In this research, the microstructure and texture evolution mechanism across the weld thickness and different FSW zones are studied. Cross-section of the weld joints developed by UwFSW and C-AFSW were investigated via transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). EBSD data of C-AFSW joints reveal that significant grain refinement occurs in the stirred zone (SZ) due to continuous dynamic recrystallization. As compared to C-AFSW, the microstructural evolution mechanism in UwFSW was found to be very complex in the different parts of the SZ. For UwFSW, discontinuous dynamic recrystallization and geometric dynamic recrystallization were found to be the main microstructural evolution mechanism in the SZ. In addition, the enhanced cooling rates of UwFSW produce a fine grain structure and a large number of high angle boundaries (HABs). Both C-AFSW and UwFSW showed mixed grain structure in the thermomechanically affected zone. TEM results showed dislocation accumulation and annihilation were predominant in UwFSW with fine and denser rod-shaped (θ́-Al₂Cu) precipitates. The shear textures (A/overline{A }), A₁*/A₂* and (B/overline{B }) are formed in the SZ of both C-AFSW and UwFSW. However, the shear components (B/overline{B }) dominates in the C-AFSW as compared to(A/overline{A }). The result and findings of this research help to understand the microstructure evolution mechanism of CuZn40/AA1100-O FSW joints and further optimize the welding process for application.

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Microalloying is a crucial method for enhancing alloy properties. Magnesium (Mg) is the primary strengthening element in 6xxx alloys, while zinc (Zn) plays a similar role in 7xxx alloys. However, the combined addition of Mg and Zn and its impact on the multi-element hypoeutectic Al-Si cast aluminum alloys remain uncertain. This paper investigates the effects of Mg and Zn additions on the solidification and microstructure of multi-element hypoeutectic Al-Si alloys. With Mg and Zn additions, the size and distribution of eutectic silicon transform from individual long platelets to a finer, more compact structure due to increased undercooling resulting from lower eutectic silicon formation temperatures. Additionally, the needle-like phases were AlSi(Mn, Cr)Fe and (Al, Zr, Si) in the A1 alloy, respectively. The incorporation of Zn into the AlSi(Mn, Cr)Fe phase, the AlSi(Mn, Cr)Fe phase has the preferred growth direction and finally presents a needle-like structure. The formation of the new phase (Al, Zr, Si) is attributed to increased partial Gibbs energy of Zr, reducing its ability to remain in the liquid phase and promoting reaction with Si upon addition of Mg and Zn. The hardness and tensile strength increase with the addition of Mg and Zn due to their solid solution into the aluminum matrix, while elongation decreases. The room temperature tensile strength, hardness, and elongation of the as-cast alloy under gravity casting reach 221.04 MPa, 84.1 HBW, and 2.12%, respectively, upon the addition of Mg and Zn in multi-element hypoeutectic Al-Si alloys. This paper provides a new direction and reference value for the development of solution-free high-strength aluminum alloys.

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A 50%-rolled Zr-2.5Nb alloy sheet was annealed in lower (700 °C) and upper (800 °C) α-Zr + β-Zr dual-phase regions, respectively, followed by water quenching. Microstructural features were meticulously characterized and analyzed using electron channeling contrast imaging and electron backscattering diffraction techniques. After annealing at 700 °C, the alloy obtains a mixed structure of recrystallized α grains and granular β phase, and the preservation of β phase can be associated with the enrichment of Nb. For the 800 °C sample, its microstructure comprises recrystallized α grains and ultrafine plates produced by martensitic transformation. There exist numerous nanotwins inside these martensitic plates, which are related to the Nb-induced reduction of martensite start temperature (M_S). Hardness tests reveal that compared to the as-rolled sample (249.8 ± 11.0 HV), the hardness of the 700 °C sample slightly drops (240.9 ± 6.7 HV) due to increased α-grain sizes and the reduced deformation defects. In contrast, there appears a notable increase in hardness for the 800 °C sample (290.0 ± 5.5 HV), which is attributed to synergistic effects of multiple mechanisms including grain refinement strengthening of martensitic laths, nanotwin boundary strengthening, and solid-solution strengthening.

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7075 aluminum alloy has significant attraction in the field of lightweight materials, but its poor wear resistance limits its application. Therefore, in this study, the optimal wear-resistant weld seam was prepared by adjusting the FSP (Friction Stir Processing). Friction and wear tests were conducted to analyze the wear resistance of the weld seam. Additionally, XRD, SEM, and TEM were used for phase analysis and microstructural characterization of the weld seam. The treated specimens exhibited the significantly higher wear rate and average coefficient of friction during the stabilization stage of samples W1 (welded rate: 60 mm/min; rotation rate: 1000 rpm) and W8 (welded rate: 80 mm/min; rotation rate: 1200 rpm), with increases of 45% and 40% for the wear rate, respectively, and 19% and 13% for coefficient of friction in comparison with the untreated material. The optimized FSP parameters can considerably improve the wear resistance of the material by affecting the heat input, which altered the grain size and distribution in the welded zone. X-Ray diffraction and scanning electron microscopy/energy dispersive spectroscopy studies provided the mechanism underlying grain size and plastic nano twin structures contributions to wear resistance.

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The present work deals with the mechanical and microstructural characterization of Al6061/3 wt% Graphene nanoplatelets (GNPs) fabricated through the bottom pouring stir casting technique. Magnesium (Mg) as a wetting agent (1 wt%) was incorporated to reduce the aggregation and increase the uniform dispersion of GNPs in the matrix. The grain structure, microhardness, tensile strength, and fractured surfaces of Al6061-based nanocomposites were investigated to better understand the effect of GNPs on the microstructure and mechanical properties of the manufactured specimens. The microchannels were machined using a 500 µm TiSiN-coated carbide end mill tool. The machinability analysis was conducted to investigate the impact of micromachining parameters on surface roughness, burr formation, and cutting force during dry machining. An image processing method was used to analyze the slot and burr widths of the fabricated microchannels. The measurements were acquired by a user-defined subroutine using scanning electron microscope (SEM) images. The SEM micrographs revealed the dendritic microstructures with reduced casting defects. The fabricated nanocomposite showed a 35% and 267% improvement in microhardness and ultimate tensile strength, respectively. SEM fractograph of the nanocomposite revealed a mixed-mode ductile–brittle failure mechanism. The optimum machining condition displayed a 52% and 36% decrease in feed force (left( {F_{y} } right)) and surface roughness (left( {R_{a} } right)), respectively, compared to the lowest process parameter. Optimum parameters revealed a 78% decrease in up-milling side burrs and a 54% improvement in slot width compared to the lowest process parameter. ANOVA results revealed feed rate as a significant factor, which contributed 83% and 93% in thrust force (left( {F_{z} } right)) and (R_{a}), respectively. Material adhesion and abrasion were identified as the primary tool wear mechanisms.

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In this work, the effect of Zn content and homogenization treatment on the mechanical properties and corrosion behavior of the Mg-Y-Zn alloys was systematically investigated. When the Zn content in the as-cast alloys is increased to 3%, the Mg₂₄Y₅ eutectic phases disappear and the lamellar LPSO phases increase significantly. In the as-homogenized alloys, the Mg₂₄Y₅ eutectic phases are not detected and a large number of intragranular lamellar LPSO phases appear. The LPSO volume fraction decreases gradually with the extension of homogenization holding time. Numerous lamellar phases are precipitated in the furnace-cooling samples. The alloys with a higher interdendritic LPSO volume fraction (WZ93) or containing fine lamellar LPSO phases (H-6#) exhibit better mechanical properties. The continuous interdendritic secondary phases can act as a corrosion barrier to block the intrusion of corrosive fluid, but the lamellar LPSO phases are conducive to the corrosive fluid into the interior of the substrate. The H-3# alloy with numerous lamellar LPSO phases exhibits the worst corrosion resistance, while the WZ92 alloy with more continuous LPSO phases shows better corrosion resistance. This work indicates that the mechanical and corrosion properties can be improved by modulating the volume fraction and morphology of LPSO phases.

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High-energy ultrasound plays an important role in enhancing the uniform distribution of reinforcing particles inside the composites. In this work, the effect of different ultrasonic power (0–1000 W) on the solidification microstructure and mechanical properties of 2.0 wt% ZL205A/TiB₂ composites was investigated. The experimental results show that, within a certain range, the increase of ultrasonic power can refine the grain size, reduce the TiB₂ particle agglomeration, and enhance the mechanical properties of composites. The grain size was reduced from 93 μm (0 W) to 49 μm (800 W), and the tensile strength (UTS) was increased from 186.5 to 230.6 MPa, respectively, a relative increase of 47.3%. However, when the ultrasonic power reaches 1000 W, the microstructure of the composites is deteriorated, the grain size is coarse, and the mechanical properties are reduced. This indicates that high ultrasonic power is not conducive to the further optimization of composite microstructure. Based on the experimental results, the mechanisms of ultrasonic power on the microstructure of the composite materials have been discussed in detail. Furthermore, the quantitative relationships between ultrasonic power and sound pressure (P), the intensity density (I), the acoustic impulse velocity (v), and amplitude (A) was established, which played an important theoretical guidance role for the preparation of metal matrix composite materials during industrial application with ultrasonic treatment.

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The main objective of this work is to explore the changes in the microstructure and mechanical properties of ZL205A/TiB₂ composite materials under the influence of different ultrasonic powers. The lattice matching relationship between TiB₂ reinforcement particles and the aluminum matrix is revealed, and the changes in acoustic energy density, sound pressure intensity, and ultrasonic amplitude under different ultrasonic powers are quantitatively analyzed.

In order to improve the performance of snow tires for automobiles, it is important to develop Kerf with an ultra-thin thickness under 0.4 mm. However, the reduced thickness requires further improved mechanical properties, such as strength, ductility and toughness. Therefore, we investigated the microstructure and mechanical properties by adjusting aging treatment conditions regarding 18Ni-300 maraging steel samples with an ultra-thin thickness of 0.4 mm, which were fabricated using the additive manufacturing technique, powder bed fusion (PBF) method. The microstructural analysis was performed using scanning-electron-microscope (SEM), electron-backscattered diffraction (EBSD) and transmission-electron-microscope (TEM). The mechanical properties were evaluated using the universal testing machine (UTM) with a strain rate of 1 × 10^− 3 s^− 1. It was found that after a single aging treatment without solution treatment, the microstructural evolutions, such as the formation of nano-precipitate and variation of volume fraction of reverted austenite were observed, which affect the strength and ductility, respectively. More specifically, the highest tensile strength of 1933.9 MPa was achieved in the sample aged at 480 ℃ for 3 h, whereas the maximum strain of 7.53% was obtained in the sample aged at 560 ℃ for 6 h. As a result, we report the aging treatment strategy to control the microstructure which can optimize the mechanical properties in the ultra-thin samples.

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