Magnetic Field-Induced Solvothermal Synthesis of One-Dimensional Assemblies of Ni Co Alloy Microstructures

One-dimensional magnetic Ni Co alloy microwires with different microstructures and differently shaped building blocks including spherical particles,multilayer stacked alloy plates,and alloy flowers,have been synthesized by an external magnetic field-assisted solvothermal reaction of mixtures of cobalt(II)chloride and nickel(II)chloride in 1,2-propanediol with different NaOH concentrations.By adjusting the experimental parameters,such as precursor concentration and Ni/Co ratio,Ni Co alloy chains with uniform diameters in the range 500 nm to 1.3μm and lengths ranging from several micrometers to hundreds of micrometers can be obtained.A mechanism of formation of the one-dimensional assemblies of magnetic NiCo microparticles in a weak external magnetic fi eld is proposed.

Evolution of microstructure and mechanical properties of A356 aluminium alloy processed by hot spinning process

The evolution of microstructure and mechanical properties of A356 aluminum alloy subjected to hot spinning process has been investigated. The results indicated that the deformation process homogenized microstructure and improved mechanical properties of the A356 aluminum alloy. During the hot spinning process, eutectic Si particles and Fe-rich phases were fragmented, and porosities were eliminated. In addition, recrystallization of Al matrix and precipitation of Al Si Ti phases occurred. The mechanical property testing results indicated that there was a significant increase of ductility and a decrease of average microhardness in deformed alloy over die-cast alloy. This is attributed to uniform distribution of finer spherical eutectic Si particles, the elimination of casting defects and to the recrystallized finer grain structure.

Synergistic effects of composition and heat treatment on microstructure and properties of vacuum die cast Al-Si-Mg-Mn alloys

The purpose of this study was to prepare high-quality Al-Si-Mg-Mn alloy with a good combination of strength and ductility employing the vacuum-assisted high-pressure die cast process. An orthogonal study of heat treatments was conducted to design an optimized T6 heat treatment process for both Al-10%Si-0.3%Mg-Mn and Al-11%Si-0.6%Mg-Mn alloys. The results demonstrate that no obvious blisters and warpage were observed in these two alloys with solid solution treatment. After the optimal T6 heat treatment of 530°C×3 h + 165°C×6 h, Al-11%Si-0.6%Mg-Mn alloy has better mechanical properties, of which tensile strength, yield strength and elongation reached 377.3 MPa, 307.8 MPa and 9%, respectively. The improvement of mechanical properties can be attributed to the high density of needle-like β″(Mg_5Si_6) precipitation after aging treatment and the fine and spherical eutectic Si particles uniformly distributed in the α-Al matrix.

Microstructure and Deformation Behavior of Ti-10V-2Fe-3Al Alloy during Hot Forming Process

The microstructure evolution and formability of Ti-10V-2Fe-3Al alloy related to the initial microstructures and processing variables were investigated during hot forming process. The experimental results show that the α-phase growth is controlled by solute diffusion during the heat treatment processes. Four different microstructures were established by combinations of several heat treatments, and Ti-10V-2Fe-3Al alloy shows excellent formability both above and below the β transus temperature. The alloy possesses low deformation resistance and active restoration mechanism during the deformation. A constitutive equation describing the hot deformation behavior of Ti-10V-2Fe-3Al alloy was obtained. Higher fl ow stress was observed for the acicular morphology of α phase in microstructures with large aspect ratios as compared with that of small aspect ratios. Due to the dynamic recovery in soft β phase, and the dynamic recrystallization and breakage of acicular α-phase, fl ow softening occurred signifi cantly during deformation. Dynamic recrystallization also occurred especially in the severely deformed regions of forged parts.

Microstructure and Hydrogen Absorption/Desorption Behavior of Mg23-xLaxNi10 Alloy

Induction melting was used as a routine method to synthesize Mg_（23）Ni_（10）, Mg_（22）LaNi_（10） and Mg_（21）La_2Ni_（10） alloys, and followed by a detailed microstructural characterization which included X-ray diffraction（XRD）, scanning electron microscopy（SEM） with energy dispersive spectrometer（EDS）, high resolution transmission electron microscope（HRTEM） and hydrogen absorption/desorption measurements. XRD analysis results showed that Mg_2Ni and Mg phases were detected in the XRD pattern of the Mg_（23）Ni_（10） alloy, however, the La addition results in conversion from Mg to LaMg_3 and La_2Mg_（17） phases and appearance of crystal defects included dislocations, twin grain boundary and vacancy in the Mg_（22）LaNi_（10） and Mg_（21）La_2Ni_（10） alloy textures. The total maximum hydrogen absorption capacity was 4.45 wt% for the Mg_（23）Ni_（10） alloy, however, the Mg_（22）LaNi_（10） and Mg_（21）La_2Ni_（10） alloys with vacancy, dislocations and twin grain boundary, absorbed 3.66 wt% and 3.60 wt%, respectively, indicating that the La addition led to decreasing of the maximum hydrogen absorption capacity. Besides, hydrogen absorption/desorption of 90% of saturated state expended for about 456 and 990 s for pristine Mg_（23）Ni_（10） alloy, by contrast, the time decreased owing to improvement of hydrogen absorption and desorption kinetics in the alloy with La element, with which the uptake time for hydrogen content to 90% of saturated state was 150 and 78 s, and 90% hydrogen can be released in 930 and 804 s for Mg_（22）LaNi_（10） and Mg_（21）La_2Ni_（10） alloys in the experimental condition.

Mechanism of Effects of Rare Earths on Microstructure and Properties at Elevated Temperatures of AZ91 Magnesium Alloy

By using real-space recursion method,the energetics of the undoped and Al and/or RE atoms doped 7（1450）〈0001〉 symmetric tilt grain boundaries（GBs）in AZ91 alloys were investigated.Similar calculations were performed on undoped and doped bulk α Mg for comparison.The results showed that Al atoms segregated at GBs in AZ91 alloys.When RE atoms were added,they also segregated at GBs,and their segregation is stronger than Al atoms＇.Therefore,RE atoms retard the segregation of Al atoms.Calculations of interaction energy indicated that Al atoms repelled each other,and could form ordered phase with host Mg atoms.On the contrary to the case of Al,RE atoms attracted each other,they could not form ordered phase with Mg,but could form clusters.Between RE and Al,there existed attractive interaction,and this attractive interaction was the origin of Al11RE3 precipitation.Precipitation of Al11RE3 particles with high melting point and high thermal stability along GB improves high temperature properties of AZ91 alloys.

Ageing Effect on Hardness and Microstructure of Al-Zn-Mg Alloys

Experimental results of the investigation on the hardness of two Al-Zn-Mg alloys [Al-10.0 Zn-4.0 Mg and Al-8.5 Zn-3.0 Mg (wt pct)] aged in the temperature range 60～310℃ for different intervals of time from 1/4 h to 168 h are presented. Both the alloys were found to show identical behaviour of hardness with ageing time. Alloy with higher Zn and Mg content had higher hardness than the alloy with lower solute content. There were three ranges of temperature in which different types of precipitates formed and affected the hardness. Some of the grain boundaries were found to migrate and precipitate free zone has been observed.

Preparation of Li-B Alloy and Study of Its Microstructure and Discharge Characteristics

A Li-B alloy has been prepared using a pretreated amorphous B powder and pure Li ingot as starting materials by continually slow addition of B powder and intensified stirring in the process of melting. The microstructure and the discharge characteristic of the materials have been investigated- Results show that the problem of temperature control in synthesis would be modified by means of continual addition of B powder, the Li7B6 would be more finely distributed in the metal Li by means of intensified stirring. The discharge characteristic of the Li-B alloy using amorphous B as starting materials is almost the same with that of using crystalline B.

Effect of Titanium Content on Microstructure and Wear Resistance of Hardfacing Alloy

The hardfacing alloys with different concentrations of titanium were deposited on carbon steel substrates by shielded metal arc welding, and the effect of titanium content on the microstructure characteristics of the hardfacing alloys was investigated. The wear resistance test of the hardfacing alloys was carried out by using a slurry rubber wheel abrasion test machine, and the wear behaviour was also studied. The results indicate that the addition of titanium can effectively promote the precipitation of the complex carbides of Nb and Ti due to the prior precipitation of titanium carbide which acts as nucleation sites for complex carbides. With the increase of titanium content, the wear resistance of the hardfacing alloys is increased gradually resulting from the refinement of microstructure and dispersive distribution of fine carbide precipitates. And the wear mechanism is mainly minimum plastic deformation with interrupted grooves due to the strengthening and protecting effects of carbide precipitates.

Effect of Trace Sc and Zr on the Mechanical Properties and Microstructure of A1 Alloy 2618

An experimental 2618(Al-Cu-Mg-Fe-Ni) alloy added with trace Sc and Zr was prepared by ingot metallurgy (IM) method. The aging behavior of the alloy was studied by Vickers hardness measurement at 200℃ and 300℃. and the tensile properties of alloy specimens were measured at 20℃, 200℃, 250℃ and 300℃. The microstructure was observed by using optical microscope, SEM and TEM. It was found that the addition of Sc and Zr to 2618 alloy resulted in a primary Al_3(Sc,Zr) phase which could refine the grain because it acts as nuclei of heterogeneous crystallization in the melt during solidification. The secondary Al_3(Sc,Zr) particles were full coherent with matrix and had obvious precipitation hardening effect. They also made the S' phase precipitate more homogeneous. So the strength of alloy increases at both ambient and elevated temperatures without a decrease of ductility. The ductile fracture of alloy occurs by microvoid nucleation, growth and coalescence, so the microvoid coalescence is the dominant fracture mechanism.

Microstructure and mechanical properties of the micrograined hypoeutectic Zn–Mg alloy

A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures： gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples＇ mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness（Hv = 122 MPa）, compressive yield strength（382 MPa）, tensile yield strength（332 MPa）, ultimate tensile strength（370 MPa）, and elongation（9%）. This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall-Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.

Effects of Heating and Hot Extrusion Process on Microstructure and Properties of Inconel 625 Alloy

The effects of the heating process and hot extrusion on the microstructure and properties of inconel 625 alloy were studied. The experimental results showed that the properties of Inconel 625 alloy could be improved through the heating process and hot extrusion concomitant with a reduced corrosion rate. The M23C6 carbide, generated in the heating process, was retained and distributed at the grain boundary during the process of hot extrusion, which had an important influence on both elongation and corrosion resistance. The improvement of the comprehensive properties of the material, as measured by a tensile test at room temperature, was correlated with the dissolution of segregation Nb. A typical ductile fracture changed to a cleavage fracture where secondary cracks could be clearly seen. With the increase of the extrusion ratio, the real extrusion temperature was higher, which led to more dissolution of the M23C6 carbide, decreased the number of secondary cracks, enhanced the effect of solid solution strengthening, and reduced the intergranular corrosion rate. Under the condition of a high extrusion ratio and a high extrusion speed, the less extrusion time made it possible to obtain organization with a smaller average grain size. Moreover, in this case, the M23C6 carbide and segregated Nb did not have enough time to diffuse. Thus all samples exhibited medium strengths and corrosion rates after extrusion.

Microstructure and mechanical properties of cryorolled AZ31 magnesium alloy sheets with different initial textures

AZ31 magnesium alloy sheets with different strong textures were cryorolled at the liquid-nitrogen temperature to the strain of 4% and 8%. The microstructure and texture of the rolled sheets were investigated via scanning electron microscopy（SEM）, electron backscatter diffraction（EBSD）, and X-ray diffraction（XRD）. The mechanical properties of the sheets were tested through in-plane uniaxial tensile tests at ambient temperature. The tensile stress was exerted in the rolling direction（RD） and transverse directions（TD）. The microstructural and textural evolutions of the alloy during cryorolling were investigated. Due to active twining during rolling, the initial texture significantly influenced the microstructural and textural evolutions of the rolled sheets. A {10 12} extension twin was found as the dominated twin-type in the cryorolled samples. After cryogenic rolling, the ductility of the samples decreased while the strength increased. Twinning also played an important role in explaining the mechanical differences between the rolled samples with different initial textures. The samples were significantly strengthened by the high stored energy accumulated from cryorolling.

Effect of Pouring Process on the Microstructures of Semi-Solid AlSi_7Mg Alloy

The effect of different pouring temperatures and different pouring heights, the distance between the mouth of the pouring ladle and the top of the mold, on the microstructure of AlSi7Mg alloy have been researched in the paper. When the pouring temperature is close to the liquidus temperature, the primary alpha -Al in 'the billets of AlSi7Mg alloy solidified into spherical and nodular fine grains distributed homogeneously. The optimum pouring temperature for semi-solid AlSi7Mg billet with spherical or nodular primary alpha -Al is 615 degreesC. At the same pouring temperature, the higher the pouring ladle, the more easily the spherical and nodular primary alpha -Al obtained in the semi-solid AlSi7Mg billet. When the pouring temperature is close to the liquidus temperature and the pouring ladle is relatively high, it is the great cooling rate, the flow of the molten allay caused by pouring and the large simultaneous solidification region induced by the near liquidus temperature, that promote the formation of spherical or nodular primary cr-Al.

Effects of process parameters on morphology and distribution of externally solidified crystals in microstructure of magnesium alloy die castings

During the cold-chamber high pressure die casting(HPDC) process, samples were produced to investigate the microstructure characteristics of AM60B magnesium alloy. Special attention was paid to the effects of process parameters on the morphology and distribution of externally solidified crystals(ESCs) in the microstructure of magnesium alloy die castings, such as slow shot phase plunger velocity, delay time of pouring and fast shot phase plunger velocity. On the basis of metallographic observation and quantitative statistics, it is concluded that a lower slow shot phase plunger velocity and a longer delay time of pouring both lead to an increment of the size and percentage of the ESCs, due to the fact that a longer holding time of the melt in the shot sleeve will cause a more severe loss of the superheat. The impingement of the melt flow on the ESCs is more intensive with a higher fast shot phase plunger velocity, in such case the ESCs reveal a more granular and roundish morphology and are dispersed throughout the cross section of the castings. Based on analysis of the filling and solidification processes of the melt during the HPDC process, reasonable explanations were proposed in terms of the nucleation, growth, remelting and fragmentation of the ESCs to interpret the effects of process parameters on the morphology and distribution of the ESCs in the microstructure of magnesium alloy die castings.

Characteristics and Microstructure of a Hypereutectic Al-Si Alloy Powder by Ultrasonic Gas Atomization Process

A hypereutectic Al-Si alloy powder was prepared by ultrasonic gas atomization process. The morphologies, microstructure and phase constituent of the alloy powder were studied. The results showed that powder of the alloy was very fine and its microstructure was mainly consisted of Si crystals plus intermetallic compound A19FeSi3, which were.very fine and uniformly distributed.

Semisolid die forging process,microstructures and properties of AZ31 magnesium alloy mobile telephone shells

A semisolid slurry of AZ31 magnesium alloy was prepared by vibrating wavelike sloping plate process,and the semisolid die forging process,microstructures,and properties of the magnesium alloy mobile telephone shell were investigated.The semisolid forging process was performed on a YA32-315 four-column universal hydraulic press.The microstructures were observed by optical microscopy,the hardness was analyzed with a model 450SVD Vickers hardometer,the mechanical properties was measured with a CMT5105 tensile test machine,and the fractograph of elongated specimens was observed by scanning electron microscopy （SEM）.The results reveal that with the increase of die forging force,the microstructures of the product become fine and dense.A lower preheating temperature and a longer dwell time are favorable to the formation of fine and dense microstructures.The optimum process conditions of preparing mobile telephone shells with excellent surface quality and microstructures are a die forging force of 2000 kN,a die preheating temperature of 250℃,and a dwell time of 240 s.After solution treatment at 430℃ and aging at 220℃ for 8 h,the Vickers hardness is 61.7 and the ultimate tensile strength of the product is 193MPa.Tensile fractographs show the mixing mechanisms of quasi-cleavage fracture and ductile fracture.

Effects of Aging Temperature on Microstructure and High Cycle Fatigue Performance of 7075 Aluminum Alloy

The hardness, the tensile and the high-cycle fatigue（HCF） performances of 7075 aluminum alloy were investigated under temper T651, solution treated at 380 ℃ for 0.5 h and aged at different temperatures（150, 170, 190 ℃） for 10 hours. The optimal microstructures and the fatigue fracture surfaces were observed. The results show that the hardness and the tensile performances are at their optimum at T651, but the fatigue life is the shortest. The hardness and the elongation are the lowest after solution treatment. With the aging temperature increasing（150-190 ℃）, the HCF is improved. The crack is initiated from the impurity particles on the subsurface. Treated at 170 ℃,the area of the quasi-cleavage plane and the width of parallel serrated sections of the crack propagation are the largest. With increasing aging temperature, the dimple size of finally fracture surfaces becomes larger and the depth deeper.

Microstructure and Mechanical Property of 2024 Aluminium Alloy Prepared by Rapid Solidification and Mechanical Milling

Rapidly solidified 2024 aluminium alloy powders were mechanically milled, then consolidated to bulk form. The microstructural changes of the powders in mechanical milling (MM) and consolidation process were characterized by X-ray diffraction analyses and transmission electron microscopy observations. The results showed that mechanical milling reduced the grain size to nanometer, dissolved the Al2Cu intermetallic compound into the aluminium matrix and produced an aluminium supersaturated solid solution. During consolidation process. the grain size increased to submicrometer, and the Al2Cu and Al2(Cu, Mg, Si, Fe, Mn) compounds precipitated owing to heating. Increasing consolidation temperature and time results in obvious grain growth and coarsening of second phase particles. The tensile yield strength of the consolidated alloy with submicrometer size grains increases with decreasing grain size, and it follows the famous HallPetch relation

Effects of Additional Elements on Microstructure and Precipitation Behaviour in Rapidly Solidified Al-Ti Base Alloys

Rapidly solidified Al-Ti base alloys were prepared by melt spinning at the cooling rate about 107 K/s. The melt-spun ribbons were used to observe the dricrostructures after heat treatment.In the supersaturated Al-Tl-Si alloy, age hardening occurred after 1 h anneal in the temperature range of 4000~500℃, which seems to be attributed to the precipitation of metastable Ll2- (Al,Si)3Ti phase. However. the microhardness was relatively low because of the low v/o and the insufflcient stability of precipitates. Thus. Cr was added to Al-Ti-Si alloys in order to stabilize the microstructures and to increase the v/o of precipitate5. As a result. the alIoys containing Cr were evaluated to possess the improved properties at the service temperature.