Influence of deformation on the corrosion behavior of LZ91 Mg-Li alloy

The effect of rolling and forging on the microstructure and corrosion behavior of LZ91 alloy was investigated using an electron probe micro-analyzer,immersion and electrochemical tests.Results showed that the area fraction of theβ-Li phase remained unchanged,and the grain size of theβ-Li phase decreased after forging.The as-rolled forged alloy(FR-LZ91)exhibited the highest area fraction of theβ-Li phase and the longest grains.The corrosion resistance of the forged LZ91 alloy increased due to grain refinement that prevented further corrosion during the immersion test.Among the experimental alloys,FR-LZ91 showed the highest resistance of corrosion film and charge transfer resistance values due to its protective film caused by the high area fraction of theβ-Li phase.

Thermo-driven oleogel-based self-healing slippery surface behaving superior corrosion inhibition to Mg-Li alloy

Bioinspired by Nepenthes, lubricant infused surfaces(LIS) have attracted widespread attention in the field of anticorrosion. However,the lubricant coating has some disadvantages such as complex construction processing and easy loss of oil phase in air or dynamic water phase. In this study, oleogel is infused into a lotus leaf inspired super-hydrophobic matrix to form an oleogel infused surface(OIS) for enhancing corrosion resistance of active Mg-Li alloy. For reserving oleogel, firstly, a facile one-step electrodeposition method is used to construct super-hydrophobic surface(SHS) composed by samarium/myristic acid complex micro-nano flower structure onto Mg-Li alloy.The coating exhibits excellent superhydrophobic property at a static contact angle of 160° by applying 30 V electrolysis for 30 min. The protection efficiency of single SHS highly relates with the metal itself. For short period immersion in water phase, SHS can afford protection to Mg-Li alloy. However, the long-term immersion will see the rapid failure of SHS, and the high activity of Mg-Li alloy is one main reason.We assume that SHS cannot be a good choice for protecting Mg-Li alloy. Then, a Nepenthes inspired liquid coating is formed by infusing oleogel into the micro-nano structure by a spin-coating method. The liquid coating performs prominent corrosion resistance with Rctreaching as high as 1.51 × 10^(10)Ω cm^(2). After the mechanical damage from the external environment, the liquid coating can realize self-repair through thermal assistance, and the liquid coating can still restore Rctup to 1.24 × 10^(10)Ω cm^(2) after healing. The corrosion resistance of the liquid coating remains strong by showing Rctas high as 1.14 × 10^(9)Ω cm^(2), even after immersion in representative corrosive 3.5 wt% Na Cl solution for 30 d.

The influence of Sc addition on microstructure and tensile mechanical properties of Mg-4.5Sn-5Zn alloys

The microstructure and tensile properties of the as-cast and as-rolled Mg-4.5Sn-5Zn alloys by adding various Sc content were investigated.Improvement of the tensile properties in as-cast Sc-containing alloys is attributed to the grain refinement and modification of secondary phase morphology.Three types of precipitates,namely spherical Mg2Sn,rod-like MgZn and Sc-rich phases were dispersed in the matrix of the Sc added M g-4.5Sn-5Zn alloys after hot rolling deformation.In addition,weakening and deflecting of the basal texture in as-rolled alloys were found and were attributed to Sc addition.Further increasing the Sc addition rate to 0.4 wt.%,however,resulted in the clustering of the Sc-rich phases and was found to reduce the tensile properties of the alloy,especially the elongation.The as-rolled Mg-4.5Sn-5Zn-0.3Sc alloy exhibits an optimum combination of tensile properties.The ultimate tensile strength,yield strength and elongation are 293.0MPa,164.2Mpa and 21.5%,respectively,and the elongation is about 68%higher than that of Sc-free alloy.

Micro Hierarchical Structure and Mechanical Property of Sparrow Hawk (Accipiter nisus) Feather Shaf

In this study,the real 3D model of the feather shaft that is composed of medulla and cortex is characterized by X-ray computer tomography,and the structural features are quantitatively analyzed.Compression and tensile tests are conducted to evaluate the mechanical performance of the feather shaft and cortex at different regions.The analysis of the 3D model shows that the medulla accounts for∼70%of the shaft volume and exhibits a closed-cell foam-like structure,with a porosity of 59%.The cells in the medulla show dodecahedron and decahedron morphology and have an equivalent diameter of∼30μm.In axial compression,the presence of medulla enhances the shaft stability.Especially,the combined effect of the medulla and cortex increases the buckling strength of the middle and distal shaft by 77%and 141%,respectively,compared to the calculated value of the shaft using linear mixed rule.The tensile properties of the cortex along the shaft axis are anisotropic because of the different fiber structures.As the fiber orientation gradually becomes uniform in the axial direction,the Young’s modulus and tensile strength of the cortex on the dorsal gradually increase from calamus to the distal shaft,and the fracture mode changes from tortuous fracture to V-shaped fracture.The cortex on the lateral shows the opposite trend,that is the distal shaft becomes weaker due to fiber tangles.

Tailoring the Microstructure and Mechanical Property of Mg-Zn Matrix Composite via the Addition of Al Element

The semi-solid stir casting method is adopted to prepare 10 wt%SiC_(p)/Mg-6Zn-0.5Ca-xAl(x=0,1,3 and 5 wt%)composites,and the microstructure evolution and mechanical property of composites with various Al content are investigated.The results show that the addition of 3 wt%Al improves the distribution of SiC_(p),whereas the SiC_(p) cluster occurs again with Al content greater than 3%.An abnormal phenomenon of twinning is observed in the cast composites in this work.The SiC_(p)/Mg-6Zn-0.5Ca composite possesses the highest twin content of~23%,for which tension twins(TTW)and compression twins(CTW)account for~19%and~3%,respectively.The CTW is only observed in ZXA600 composite.The addition of Al has an inhibiting effect for the generation and growth of twins.The content of twin decreases firstly and then increases with increase of Al content.The lowest twin content is obtained as Al increases to 3 wt%.It is found the existence of twin is detrimental to the mechanical property of composites.As-cast SiC_(p)/Mg-6Zn-0.5Ca-3Al composite with the lowest twin content exhibits the optimal mechanical property of yield strength,ultimate tensile strength and elongation for 100 MPa,188 MPa and 4.4%,respectively.The outstanding mechanical property is attributed to the uniform distribution of SiC_(p),the low twin content and the well-distributed fine second phases.

Grain nucleation and growth behavior of a Sn-Pb alloy affected by direct current： An in situ investigation

In situ synchrotron X-ray radiography was used to study the effect of direct current（DC） on the grain nucleation and growth of Sn-50 wt.%Pb alloy. The results showed that applying DC adequately during solidification could effectively enhance the grain nucleation and inhibit its growth. Imaging of comparative experiments with varying DC intensity indicated that the final grain size, determined by the competition between grain nucleation and growth, was sensitively dependent on the DC intensity. It was found that the average grain size was decreased from 1632 to 567 μm with DC density of 1.5 A/mm^2 compared to the case without DC. Beyond this value, raising the current density may cause a significant decrease in the nucleation rate, and thus lead to a coarsening of the grain structure.

Microstructural characteristics and mechanical behavior of B4Cp/6061Al composites synthesized at different hot-pressing temperatures

B4Cp/6061Al composites have become important structural and functional materials and can be fabricated by powder metallurgy and subsequent hot rolling. In this work, the effects of the hot-pressing temperature on microstructures and mechanical behaviors of the B4Cp/6061Al composites were investigated. The results showed that compared with the T4 heat treated B4Cp/6061Al composite hot pressed at 560℃, the yield strength and failure strain of the composites hot pressed at 580℃ were increased to 235 MPa and 18.4%, respectively. This was associated with the interface bonding strength between the B4C particles and the matrix. However, the reaction products, identified to be MgAl2O4 phases, were detected in the composites hot pressed at 600℃. The formation of the MgAl2O4 phases resulted in the Mg depletion, thus reducing the yield strength to 203.5 MPa after the T4 heat treatment due to the effect of the solid solution strengthening being weakened. In addition, the variation of hardness and electrical conductivity was mainly related to the Mg content in the matrix. Based on the as-rolled microstructures observed by SEM, SR-μCT and fracture surfaces, the deformation schematic diagram was depicted to reflect the tensile deformation process of the composites.

Enhancing mechanical properties and corrosion resistance of nickel-aluminum bronze via hot rolling process

The mechanical properties and corrosion behavior of as-cast, as-annealed and hot-rolled nickelaluminum bronze(NAB) alloy(Cu-9 Al-10 Ni-4 Fe-1.2 Mn, all in wt.%) in 3.5 wt.% Na Cl solution were investigated. The results show that annealing introduces a large number of k phases to precipitate in the k phase. However, after further hot rolling, the original continuous k phases are spheroidized and dispersed, increasing the strength, hardness, and elongation of the alloy. In addition to the enhanced mechanical properties, the corrosion resistance of the NAB samples is also improved significantly by hot rolling, as revealed by the mass loss measurements, electrochemical impedance spectroscopy(EIS), and cross-sectional corrosion morphology. Selective phase corrosion occurs by the preferential corrosion of the k phase, which acts as an anode to the k phases, and the uncorroded k phases are retained in the corrosion product film. The interfaces between the k phases and the surrounding corrosion products become discontinuous caused by the spheroidization of k phases, reducing the corrosion of the substrate by the corrosive medium via the channels. As a result, the corrosion rate and the maximum local corrosion depth of the hot-rolled NAB sample are greatly reduced.

A promising new class of plasticine: Metallic plasticine

Soft, malleable, and non-dry on exposure in air are the typical features for plain plasticine, which lead plasticine to be widely used in many industrial fields and our daily life. As a kind of clay, poorly elec- tric conductivity and thermal conductivity of plain plasticine seriously limit its applications. Therefore, synthesizing a kind of plasticine having metallic bond is of importance for extending its applications in some special cases, such as thermal-cooling medium, anti-static electricity, electromagnetic shielding, etc. Here, we report a novel GalnSnCdZn2 alloy, which exhibits similar behavior as compared to those of plasticine at near room temperature （30-40 ℃）, and a good electrical conductivity due to its nature of metal. This new GalnSnCdZn2 alloy can be called as metallic plasticine that contains the near-eutectic structure with low melting point and the other relatively high melting point phases. In this metallic plas- ticine, the near-eutectic structure with low melting point plays the same role as the oily ingredient in plain plasticine, dominating the plastic deformation, while the other relatively high melting point phases act as the stuffing like the CaCO3 in plain plasticine. The creation of metallic plasticine offers a general strategy for designing/preparing a new class of plasticine which possesses both the nature of metal and plasticine.

Top-down method to fabricate TiNi_(1+x)Sn half-Heusler alloy with high thermoelectric performance

The top-down method was used to fabricate the TiNi_(1+x)Sn half-Heusler alloy.Several knotty problems have been solved using the top-down method,including the generation of impurity phases,the visible discrepancy in the grain size of the TiNi_(2)Sn second phase,and irregular variations in the Seebeck coefficient(S),electrical conductivity(σ),and thermal conductivity(κ)with increasing Ni content.The generation of a large number of incoherent interfaces between the half-Heusler(HH)and full-Heusler(FH)phases fabricated by the top-down method drastically improved and retained κ and S,thereby leading to an enhancement in the dimensionless figure of merit(ZT)by~19%for the TiNi_(1.05)Sn sample as compared to the ZT of the samples prepared by the conventional method.

Ultrasound-Assisted Solidifi cation of a Cu–Cr Alloy

Ultrasonic cavitation radiates huge power in a small solidifying bulk,leading to significant grain refinement,purification and homogenization of the final alloys.Ultrasound vibration has mostly been used for treating the solidification of light metals,but it is difficult to directly introduce ultrasonic vibration into copper alloy due to the lack of proper sonotrode.In this work,we have used a Sialon ceramic sonotrode to propagate acoustic waves in a Cu-Cr alloy melt.Significant grain refinement and modification of primary Cr have been obtained.With the ultrasound vibration treatment,the mechanical properties of the as-cast Cu-Cr alloy have been improved.The wear resistance of the Cu-Cr alloy has also shown enhancement with respect to the untreated alloy.