Gaseous and Electrochemical Hydrogen Storage Kinetics of As-quenched Nanocrystalline and Amorphous Mg_2Ni-type Alloys

The nanocrystalline and amorphous Mg2Ni-type Mg2Ni1-xCox （x = 0, 0.1, 0.2, 0.3, 0.4） alloys were synthesized by melt quenching technology. The structures of the as-cast and quenched alloys were characterized by XRD, SEM and HRTEM. The gaseous hydrogen storage kinetics of the alloys was measured using an automatically controlled Sieverts apparatus. The alloy electrodes were charged and discharged with a constant current density in order to investigate the electrochemical hydrogen storage kinetics of the alloys. The results demonstrate that the substitution of Co for Ni results in the formation of secondary phases MgCo2 and Mg instead of altering the major phase Mg2Ni. No amorphous phase is detected in the as-quenched Co- ffee alloy, however, a certain amount of amorphous phase is clearly found in the as-quenched alloys substituted by Co. Furthermore, both the rapid quenching and the Co substitution significantly improve the gaseous and electrochemical hydrogen storage kinetics of the alloys, for which the notable increase of the hydrogen diffusion coefficient （D） along with the limiting current density （IL） and the obvious decline of the electrochemical impedance generated by both the Co substitution and the rapid quenching are basically responsible.

An Experimental Artificial Neural Network Model:Investigating and Predicting Effects of Quenching Process on Residual Stresses of AISI 1035 Steel Alloy

The present study establishes a new estimation model using an artificial neural network(ANN) to predict the mechanical properties of the AISI 1035 alloy.The experiments were designed based on the L16 orthogonal array of the Taguchi method.A proposed numerical model for predicting the correlation of mechanical properties was supplemented with experimental data.The quenching process was conducted using a cooling medium called “nanofluids”.Nanoparticles were dissolved in a liquid phase at various concentrations(0.5%,1%,2.5%,and 5% vf) to prepare the nanofluids.Experimental investigations were done to assess the impact of temperature,base fluid,volume fraction,and soaking time on the mechanical properties.The outcomes showed that all conditions led to a noticeable improvement in the alloy's hardness which reached 100%,the grain size was refined about 80%,and unwanted residual stresses were removed from 50 to 150 MPa.Adding 5% of CuO nanoparticles to oil led to the best grain size refinement,while adding 2.5% of Al_(2)O_(3) nanoparticles to engine oil resulted in the greatest compressive residual stress.The experimental variables were used as the input data for the established numerical ANN model,and the mechanical properties were the output.Upwards of 99% of the training network's correlations seemed to be positive.The estimated result,nevertheless,matched the experimental dataset exactly.Thus,the ANN model is an effective tool for reflecting the effects of quenching conditions on the mechanical properties of AISI 1035.

Residual stress in quenched 7075 aluminum alloy thick plates

The influence of quenching water temperature, pre stretching amount and aging temperature and times on residual stress in 7075 aluminum thick plate was studied by the measurement of residual stress using drilling hole method. The results indicate that residual stress decreases by 30% with increasing quenching water temperature from 40 ℃ to 80 ℃, 20% with increasing aging temperature from 100 ℃ to 180 ℃,and 20% with increasing aging times from 5 h to 25 h. Also, residual stress decreases to zero with increasing pre stretching amount to approximately 2%. Hence, residual stress in 7075 aluminum thick plate is reduced by the control of quenching water temperature at 80 ℃ and with pre stretching amount of about 2%. An optimal aging temperature and time should be systemically investigated to obtain combination of high mechanical performances and lower residual stress for manufacturing of 7075 aluminum alloy thick plates.

Cyclic Fatigue Fracture of Zr_(55)Al_(10)Ni_5Cu_(30) Bulk Amorphous Alloy with Quenched-in Crystallites

The effects of quenched-in crystallites on the fracture of bulk amorphous alloys under cyclic loading condition wereinvestigated in this paper. For the fully amorphous alloy and specimen with fine crystallites the fatigue crack initiationoccurred on the surface. For the specimen with larger crystallites the crack originated from a big broken crystallitenear the surface. The average striation spacing on amorphous area is much larger than that on the crystallite.Crack initiation occurred at the crystallites is due to that the brittle crystallites broke easily under cyclic deformationcondition. The fine crystallites seemed to be protruded from the amorphous matrix and some bulges appeared onthe surface of specimen with fine crystallites under cyclic loading.

Characterizations of Skeletal Iron Catalysts Prepared from Rapidly and Naturally Quenched Fe-Al Alloys

Surface morphology, physical-chemical properties of skeletal iron catalysts prepared by leaching of the rapidly quenched(RQ) and naturally quenched(NQ) Fe-Al alloys with an aqueous solution of NaOH were characterized by using a series of techniques including XRD, BET, XPS, SEM, H_2 and CO-TPD. It was found that the RQ skeletal iron catalyst exhibits a smaller particle size, larger specific surface area and pore volume than the NQ one. The H_2 and CO-TPD experiments showed that the RQ skeletal iron exhibits stronger affinity for H_2 and milder affinity for CO compared with the NQ one. But the NQ skeletal catalyst shows a better thermal stability than the RQ catalyst.

Structural Characteristics of Rapidly Quenched Al-Si Alloys

The structure of rapldly quenched Al-Si alloys (1 and 4 wt-%Si) was systematically studied by optical and transmission electron microscopy (TEM ) as welI as X-ray djffractjon (XRD). ExperimentaIresults show that rapid solidification refines the grain size. extends the solid solubility of Si in Al and Introduces a high density ot defects which exist in the forms of vacancies, dislocations and dislocation loops. etc.. The decomposition process of the alloys was fol lowed by using differential scanning calorimeter (DSC) and the activation energy for precipitation of Si was obtained through Kissinger analysis. The precipitation behaviour of Supersaturated Si in both samples was further examined by TEM. It was found that Si mainly precipitated inside the grains in Al-1 wt-%Si alloy. while in Al-4 wt-%Si alloy. nearly all the Si precipitates distributed along the grain boundaries. This may be due to the structure difference between the alloys in as-quenched state

Hydrogen Absorption and Electrochemical Properties of As-Quenched Nanocrystalline Mg20Ni10 – xCux (x = 0 – 4) Alloys

Nanocrystalline Mg2Ni-type alloys with nominal compositions of Mg20Ni10 – xCux (x = 0, 1, 2, 3, 4) were synthesized by rapid quenching technique. The microstructures of the as-cast and quenched alloys were characterized by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinetics of the alloys were measured using an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system. The results show that all the as-quenched alloys hold a typical nanocrystalline structure, and the rapid quenching does not change the major phase Mg2Ni. The hydrogen absorption and desorption capacities of the alloys significantly increase with rising quenching rate. Additionally, the rapid quenching significantly improves the electrochemical hydrogen storage capacity of the alloys, but it slightly impairs the cycle stability of the alloys.

MICROSTRUCTURE OF AS-MELT-QUENCHED Ti-Si-Nd ALLOY

Rapid liquid quenching was accomplished by using an arc-melting piston and anvil apparatus.A small amount of the rare earth element Nd in melt quenched Ti80Si2o alloy promotes eutectic precipitation of β-Ti and Ti5Si3.An orientation relationship of the Ti5Si3 and the β-Ti phase is <2113>∥<001>β-Ti,(0110)∥(110)β-Ti.The alloy forming heat of the Ti5Si3 is more negative than that of the β-Ti phase and the Ti5Si3 precipitates first.

Influence of quench-induced precipitation on aging behavior of Al-Zn-Mg-Cu alloy

The effects of quenching and aging （T6, T7 and RRA） on the microstructural evolution of an A1-Zn-Mg-Cu alloy were investigated by hardness test, optical microscopy （OM）, transmission electron microscopy （TEM） and differential scanning calorimetry （DSC） measurements. It is found that the hardness of T6 aged sample after water-quenching is the highest. The quench sensitivities of T7 and RRA are almost the same, which are 1.2% higher than that of T6. TEM observation shows that the quench sensitivity for the studied alloy is mainly caused by heterogeneous precipitation during slow quenching. Many r/phases precipitate on A13Zr dispersoids inside recrystallized grains and at （sub） grain boundaries, while T and S phases form in the substructure with high density of dislocations and defects. After aging, the η＇ precipitates are coarser in the vicinity of equilibrium r/phase. However, the size and morphology of the precipitates show different characteristics among T6, T7 and RRA treatments. The DSC results are highly consistent with the TEM observation. The DSC curves of T6 aged samples are different from those of T7 and RRA aged samples, which also reflects the differences on the microstructure.

Effect of homogenization time on quench sensitivity of 7085 aluminum alloy

The effect of homogenization time on quench sensitivity of a cast 7085 aluminum alloy was investigated by means of end-quenching test, optical microscope （OM）, scanning electron microscope （SEM） and transmission electron microscope （TEM）. The results show that with the increase of homogenization time from 48 h to 384 h, quench sensitivity increased slightly as the largest difference in the hardness was increased from 5.2% to 6.9% in the end-quenched and aged specimens. Prolonging homogenization had little effect on the grain structure, but improved the dissolution of soluble T phase and resulted in larger Al3Zr dispersoids with a low number density. Some small quench-induced η phase particles on Al3Zr dispersoids were observed inside grains during slow quenching, which decreased hardness after subsequent aging. The change in the character of Al3Zr dispersoids exerted slight influence on quench sensitivity.

Exfoliation corrosion behavior of 7050-T6 aluminum alloy treated with various quench transfer time

The exfoliation corrosion （EFC） behavior of 7050-T6 aluminum alloy treated with various quench transfer time after solution heat treatment was investigated by standard EFC immersion tests, strength loss measurements after EFC tests and electrochemical impedance spectroscope （EIS） technique. The results showed that EFC resistance of the alloy decreased with increasing quench transfer time. Backscattered electron scanning electron microscope （SEM） together with transmission electron microscope （TEM） observations revealed that the coverage ratio and microstructure of precipitates at grain boundary area are the most important factors which influence the EFC susceptibility of the alloy, while precipitate-free zone （PFZ） near grain boundary has no or only a minor effect on it. In addition, galvanostatic measurements of the alloy present a good correlation between EFC resistance and transients in potential. The cumulated number of transients in potential can be used to evaluate EFC resistance of the alloy.

Time-temperature-property curves for quench sensitivity of 6063 aluminum alloy

The quench sensitivity of 6063 alloy was investigated via constructing time-temperature-property（TTP） curves by interrupted quenching technique and transmission electron microscopy（TEM） analysis.The results show that the quench sensitivity of 6063 alloy is lower than that of 6061 or 6082 alloy,and the critical temperature ranges from 300 to 410℃ with the nose temperature of about 360℃.From TEM analysis,heterogeneous precipitate β-Mg2Si is prior to nucleate on the（AlxFeySiz） dispersoids in the critical temperature range,and grows up most rapidly at the nose temperature of 360℃.The heterogeneous precipitation leads to a low concentration of solute,which consequently reduces the amount of the strengthening phase β＇＇ after aging.In the large-scale industrial production of 6063 alloy,the cooling rate during quenching should be enhanced as high as possible in the quenching sensitive temperature range（410-300℃） to suppress the heterogeneous precipitation to get optimal mechanical properties,and it should be slowed down properly from the solution temperature to 410℃ and below 300℃ to reduce the residual stress.

Simulation of temperature and stress in 6061 aluminum alloy during online quenching process

The cooling curves of 6061 aluminum alloy were acquired through water quenching experiment. The heat transfer coefficient was accurately calculated based on the cooling curves and the law of cooling. The online quenching process of complex cross-section profile was dynamically simulated by the ABAQUS software. The results suggest that the heat transfer coefficient changes during online quenching process. Different parts of the profile have different cooling velocity, and it was verified by water quenching experiment. The maximum residual stress of the profile was predicted using FEM simulation based on ABAQUS software The relations between the temperature and stress were presented by analyzing the data of key points.

Optimum design of flow distribution in quenching tank for heat treatment of A357 aluminum alloy large complicated thin-wall workpieces by CFD simulation and ANN approach

Based on the computational fluid dynamics （CFD） method, a quenching tank with two agitator systems and two flow-equilibrating devices was selected to simulate flow distribution using Fluent software. A numerical example was used to testify the validity of the quenching tank model. In order to take tank parameters （agitation speed, position of directional flow baffle and coordinate position in quench zone） into account, an approach that combines the artificial neural network （ANN） with CFD method was developed to study the flow distribution in the quenching tank. The flow rate of the quenching medium shows a very good agreement between the ANN predicted results and the Fluent simulated data. Methods for the optimal design of the quenching tank can be used as technical support for industrial production.

Quench sensitivity of 6351 aluminum alloy

The quench sensitivity of 6351 alloy was determined by the time temperature-transformation（TTT） curves and time temperature-property（TTP） curves by an interrupted quench technique with measurement of as-aged hardness and as-quenched electro-conductivity.The microstructure transformation during isothermal treatment was studied by the transmission electron microscopy（TEM） and Avrami equation.The results showed that the electro-conductivity of the 6351 alloy increased and the hardness decreased with prolonging the holding time at a certain isothermal temperature.The TEM observation indicated that the supersaturated solid solution decomposed and needles β″ precipitated at the initial stage of isothermal holding.With the prolongation of holding time at the nose temperature,rod β＇ and plate β phases formed.The isothermal transformation rate at 360℃ was the fastest,and became slow at 280℃ and reached the slowest at 440℃.The nose temperatures of the TTT and TTP curves were about 360℃ and the high quench sensitive temperature range was 230 430℃.The quench factor analysis indicated that the cooling rate should be more than 15℃/s in the quench sensitive areas in order to get optimal mechanical properties.

Grain structure effect on quench sensitivity of Al-Zn-Mg-Cu-Cr alloy

The effect of grain structure on quench sensitivity of an Al-Zn-Mg-Cu-Cr alloy was investigated by hardness testing, optical microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and scanning transmission electron microscopy. The results show that with the decrease of quenching rate from 960 ℃/s to 2 ℃/s, the hardness after aging is decreased by about 33% for the homogenized and solution heat treated alloy（H-alloy） with large equiaxed grains and about 43% for the extruded and solution heat treated alloy（E-alloy） with elongated grains and subgrains. Cr-containing dispersoids make contribution to about 33% decrement in hardness of the H-alloy due to slow quenching; while in the E-alloy, the amount of（sub） grain boundaries is increased by about one order of magnitude, which leads to a further 10% decrement in hardness due to slow quenching and therefore higher quench sensitivity.

CFD-supported optimization of flow distribution in quench tank for heat treatment of A357 alloy large complicated components

The flow distribution in quench tank for heat treatment of A357 alloy large complicated components was simulated using FLUENT computational fluid dynamics（CFD） software.The flow velocity and the uniformity of flow field in two types of quench tanks（with or without agitation system） were calculated.The results show that the flow field in the quench tank without agitation system has not evident regularity.While as for the quench tank with agitation system,the flow fields in different parameters have certain regularity.The agitation tanks have a distinct advantage over the system without agitation.Proper process parameters were also obtained.Finally,the tank model established in this work was testified by an example from publication.This model with high accuracy is able to optimize the tank structures and can be helpful for industrial production and theoretical investigation in the fields of heat treatment of large complicated components.

Surface quality, microstructure and mechanical properties of Cu-Sn alloy plate prepared by two-phase zone continuous casting

Cu-4.7%Sn （mass fraction） alloy plate was prepared by the self-developed two-phase zone continuous casting （TZCC） process. The relationship between process parameters of TZCC and surface quality of the alloy plate was investigated. The microstructure and mechanical properties of the TZCC alloy plate were analyzed. The results show that Cu-4.7%Sn alloy plate with smooth surface can be obtained by means of reasonable matching the entrance temperature of two-phase zone mold and the continuous casting speed. The microstructure of the TZCC alloy is composed of grains-covered grains, small grains with self-closed grain boundaries, columnar grains and equiaxed grains. Compared with cold mold continuous casting Cu-4.7%Sn alloy plate, the room temperature tensile strength and ductility of the TZCC alloy plate are greatly improved.

Effect of quenching rate on microstructure and stress corrosion cracking of 7085 aluminum alloy

The influence of quenching rate on microstructure and stress corrosion cracking （SCC） of 7085 aluminum alloy was investigated by tensile test, slow strain rate test （SSRT）, combined with scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electrochemical test. The results show that with decreasing the quenching rate, the size and inter-particle distance of the grain boundary precipitates as well as precipitation free zone width increase, but the copper content of grain boundary precipitates decreases. The SCC resistance of the samples increases first and then decreases, which is attributed to the copper content, size and distribution of grain boundary precipitates.