Grain refinement of pure aluminum by direct current pulsed magnetic field and inoculation

The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% （mass fraction） Al5Ti-B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μn.

Constitutive equations of 1060 pure aluminum based on modified double multiple nonlinear regression model

In order to study the work-ability and establish the optimum hot formation processing parameters for industrial 1060 pure aluminum, the compressive deformation behavior of pure aluminum was investigated at temperatures of 523?823 K and strain rates of 0.005?10 s?1 on a Gleeble?1500 thermo-simulation machine. The influence rule of processing parameters (strain, strain rate and temperature) on flow stress of pure aluminum was investigated. Nine analysis factors consisting of material parameters and according weights were optimized. Then, the constitutive equations of multilevel series rules, multilevel parallel rules and multilevel series &parallel rules were established. The correlation coefficients (R) are 0.992, 0.988 and 0.990, respectively, and the average absolute relative errors (AAREs) are 6.77%, 8.70% and 7.63%, respectively, which proves that the constitutive equations of multilevel series rules can predict the flow stress of pure aluminum with good correlation and precision.

ELECTROCHEMICAL NOISE ANALYSIS OF PURE ALUMINUM IN SODIUM CHLORIDE SOLUTION WITH WAVELET TRANSFORM TECHNIQUE

Wavelet transforms (WT) are proposed as an alternative tool to overcome the limitations of Fourier transforms (FFT) in the analysis of electrochemical noise (EN) data. The most relevant feature of this method of analysis is its capability of decomposing electrochemical noise records into different sets of wavelet coefficients, which contain information about the time scale characteristic of the associated corrosion event. In this context, the potential noise fluctuations during the free corrosion of pure aluminum in sodium chloride solution was recorded and analyzed with wavelet transform technique. The typical results showed that the EN signal is composed of distinct type of events, which can be classified according to their scales, i.e. their time constants. Meanwhile, the energy distribution plot (EDP) can be used as 'fingerprints' of EN signals and can be very useful for analyzing EN data in the future.

ELECTROCHEMICAL NOISE FEATURES OF PURE ALUMINUM DURING PITTING CORROSION IN NEUTRAL NaCl SOLUTION

Spontaneous electrochemical noise (EN) can be a rich source of information concerning the processes simultaneously occurring at a corroding interface. Potential noise fluctuations during the free corrosion of pure aluminum in different concentration of neutral sodium chloride solution are investigated, and the breakdown and restoration of passive metal's film are studied using potentiodynamic scanning (PDS) measurements and electrochemical impedance spectroscopy (EIS) technique. Two capacitance loops are observed in the Nyquist plots in two kinds of concentration, and the corrosion process is under activation control at first, then become diffusion control within the oxide film and corrosion products of (Al(OH)p-mCl-m) accumulated on the surface of the corroding electrode. It is suggested that the pitting corrosion is much easier to occur for pure aluminum in 7.0wt% than in 2.0wt% NaCl solution, and the high concentration of chloride ion in solution inhibits the repassivation of a metastable pit. The corrosion rate deterministic step does not involve Cl-.

EVOLUTION OF THE ELECTROCHEMICAL CHARACTERISTICS DURING PITTING CORROSION OF PURE ALUMINUM IN SODIUM CHLORIDE SOLUTION

The corrosion behavior of pure aluminum in neutral 3.0% （mass fraction） sodium chloride （Na-Cl） solution has been studied using electrochemical impedance spectroscopy （EIS） measurement in conjunction with the scanning electron microscopy （SEM） technique. EIS information on the evolution of pitting corrosion over a period of 15 days has been obtained and analyzed with equivalent circuit technique. The results shown that, during the ensemble constant immersion time, two time constants involved, the high frequency one originated from the protective layer on the corroding surface while the low frequenO, one from the diffusion process or the corrosion reaction and so on. And there existed a period for oxide film to growth and thickening prior to the of the attacking of chloride ions to the substrate. Meanwhile, good relationship between EIS and the material corrosion type/severity has been obtained, which has been interpreted according to the characteristics of corrosion process such as auto acceleration of pitting corrosion and the protection of local anodic reaction to the area around them.

Effect of strain rate on microstructural evolution and thermal stability of 1050 commercial pure aluminum

Effects of strain rate on the microstructure evolution and thermal stability of1050commercial pure aluminum processed by means of split Hopkinson pressure bar(SHPB)and Instron?3369mechanical testing machine were investigated.Samples in the deformed state and after various annealing treatments at423?523K(150?250°C)for1h were characterized by TEM and hardness test.The result reveals that the samples in the deformed state were mainly composed of elongated subgrains/cells with high density of dislocations.Microstructures of the quasi-static compressed aluminum were quite stable throughout the temperature range studied,and no significant grain growth was observed.However,for the dynamic impacted one,recrystallized grains with an average grain size of4.7μm were evolved after annealing at523K(250°C)for1h.It is suggested that the annealing behavior of this dynamic deformed aluminum is a continuous process of grain coarsening,rather than the traditional discontinuous recrystallization for the quasi-static compressed aluminum.

Study on resistance spot brazing process and joint performance of pure aluminum 1060/galvanized steel

Resistance spot brazing was used to perform the lap test of pure aluminum 1060 and SGCC hot-dip galvanized steel plate,the joint interface structure was studied,and the mechanical properties of the joint were tested.The results show that the aluminum-silicon(Al-Si)alloy solder used in the test has good wetting,and an intermetallic compound with a double-layer structure and uneven thickness is produced at the welded joint interface after welding.The thickness is<10μm.The welding current is at 7.8 kA,the tensile shear load of the joint reaches a peak value of about 4.72 kN.Under the same process parameters,the tensile shear load of the resistance spot brazed joint is significantly higher than that of the spot welded joint.The joint fracture mostly occurs on the aluminum plate side,and mainly at the heat-affected zone and not at the welding point.It indicates that the quality of the spot brazed joint is good,but due to the local"unbrazed"defect on the aluminum side interface of the weld,tensile stress will occur at the weld interface and the stress effect on the intermetallic compound.It is easy to produce cracks.

Micro-plasticity Constitutive Model Taking Account of Size Effects for Pure Aluminum by Microindentation

The macro-plasticity power function constitutive model （MPFCM）, the modified macro- plasticity power function constitutive model （MMPFCM） and the micro-plasticity constitutive model （MCM） taking the material intrinsic length were established to characterize the microindentation size effects of pure aluminum, respectively. The experimental results indicated MPFCM only determined precisely in the great indentation load. While a modified one named MMPFCM was subsequently established taking account of the parameters variation with the increase of indentation depth. The conventional dimensional analysis method was employed to determine the strength coefficient K and the strain hardening exponent n of this modified model. And then MCM taking account of size effects was proposed based on the Taylor dislocation model. The first- order steepest gradient descent method was adopted to obtain the material intrinsic length for the geometrically necessary dislocations. The parameters of MCM were identified by using the UMAT subroutine of ABAQUS software. The average absolute relative error of MCM is relatively lower than that of the macro-one. Although the precision of the modified one is also high, the applied scope is limited, only for the microindentation material. In addition, the intrinsic length 5.09 bun of pure aluminum is also obtained based on the strain gradient theory.

Deformation Behavior and Microstructure Evolution during Equal Channel Angular Pressing of Pure Aluminum

The deformation behavior of equal channel angular pressing(ECAP)was discussed by using plasticity method.The node mapping method is employed to realize the analysis of multi-pass ECAP by using three-dimensional FEM methods for pure aluminum.The single-pass ECAP is a non-uniform shear deformation process in the cross-section of the workpiece.The uniform deformation processing routes are obtained during multi-pass ECAP process.In addition,the density of dislocations and defects of crystal lattice are also largely changed for different processing routes.The grain microstructure is gradually refined with the increase of the pressing passes.The grains and their distribution obtained by route Bc are more useful for producing the material with high angle grain boundaries.The grain microstructure of the cross section of the pressed material decreases with the increase of strain,and some grains exhibit transformed grain boundary(PTB)fringes.The dislocation density in the grain decreases,and the grain boundary presents equiaxed distribution.

Hydrogen Solubility in Liquid and Solid Pure Aluminum—Critical Review of Measurement Methodologies and Reported Values

Reliable information on the solubility of hydrogen in aluminum and its alloys is critical to the effort of the aluminum industry to control and ameliorate the usually deleterious effects of hydrogen on the properties and performance of pure aluminum and aluminum alloy products. Unfortunately, there is a significant disparity between published values of hydrogen solubility in pure aluminum and aluminum alloys. This is because the measurement of the extremely low soluble hydrogen concentration in aluminum and its alloys is experimentally difficult. Also, the reproducibility, accuracy, and reliability of the hydrogen solubility values are very sensitive to the measurement techniques, test conditions, chemical composition, and state of the aluminum sample. Thus, no serious discussion of the reliability of reported values of hydrogen solubility in aluminum and its alloys can be undertaken without a critical assessment of the fundamental principles of the experimental techniques used in the determination of the reported values. In this article, a critical review of the fundamental principles of the experimental techniques used in the measurement of hydrogen solubility in liquid and solid pure aluminum and aluminum alloys is presented. In addition, the reliability and possible accuracy of reported values of hydrogen solubility in solid and liquid pure aluminum are critically assessed. Empirical equations for calculating hydrogen solubility in liquid and solid pure aluminum as a function of temperature and pressure, derived from the most reliable sets of data are recommended. At 101.3 kPa (1 atm.) hydrogen partial pressure, the most reliable values of hydrogen solubility at the melting point (833 K) of pure aluminum are 0.71 cm3/100g (i.e., 6.32 × 10-5 wt.% H) and 0.043 cm3/100g (i.e., 3.81 × 10-6 wt.% H), in the liquid and solid state, respectively. So, the partition coefficient of hydrogen in pure aluminum is 0.061.

Experimental and numerical investigation on pure aluminum by ECAP

The equal channel angular pressing(ECAP)experiments were carried out with industrial pure aluminum and an in-house mould.The comparison of material grain size before and after ECAP was performed by applying the technique of electron back scattered diffraction(EBSD).The results show that the grains in the material after ECAP are refined and the yield stress and ultimate strength are increased.In order to investigate the deformation mechanism during ECAP and the reason for driving grain size refinement,three-dimensional numerical simulations of the ECAP process were carried out.Based on the Lode parameter analysis, the deformation of the material sample is found very complicated,not just pure shear during extrusion through the angular channel. The simulation confirms that a strong strain gradient in the sample material is imposed by the ECAP.

Corrosion behavior of pure aluminum in FeCl_3 solution

The corrosion behavior of pure aluminum in FeCl3 solution was investigated mainly by in-situ AFM(Atomic Force Microscopy).The results of combined researches of AFM,SEM(Scanning Electron Microscopy)and EDAX(Energy Dispersive Analysis of X-ray)show that in addition to uniform attack,pitting corrosion takes place also on pure aluminum surface in FeCl3 solution at open-circuit potential,and impurity elements Fe and Cu are found enriched in corrosion product.In-situ AFM was also used to examine the initiation and development of pitting corrosion of pure aluminum induced by potentiodynamic sweep,and the repassivation of an active pit is observed.AFM tip scratching technique was used to produce a physical defect on metal surface,which is traced by in-situ AFM and it is found that the defect is likely to be preferentially attacked and evolve to pitting corrosion.

Crystallography and refining mechanism of (Ti,B)-contained salts in pure aluminum

It is shown from experiment that the pure B contained salt exhibits little refining effect, while the pure Ti contained salt, especially the salt containing 5Ti/1B, shows obvious refining effect on the pure aluminum. Crystallographic study indicates that Al3Ti particle is a more suitable nucleation site for the aluminum matrix than (Ti, Al)B2 type particles (TiB2, AlB2 and (Ti,Al)B2), because there exist more coherent planes with aluminum matrix in the former. Thermodynamics estimation, X-ray diffraction (XRD) and SEM detection show that the refining mechanism of (Ti, B)-contained refiners is mainly contributed to the heterogeneous nuclei of fine Al3Ti particles dispersed in the melting, which comes from the reaction between the Ti and aluminum. (Al, Ti)B2 type particle shows little or no direct refining effect, but it will reduce the size of Al3Ti since the Al3Ti nucleates and grows along the (Al, Ti)B2 type particle interface.

Influence of cerium and yttrium addition on strength and electrical conductivity of pure aluminum alloys

To develop pure aluminum alloys with high conductivity and strength, Al-0.2Ce and Al-0.2Ce-0.1Y alloys were prepared by rolling and annealing processes in this study. The effects of trace rare earth elements on the strength and electrical conductivity of the pure aluminum alloys were investigated. It is revealed that the addition of Ce and Y to pure aluminum can effectively enhance the strength and electrical conductivity of the alloys. In Al-0.2Ce, the addition of Ce can effectively refine the grain size of a-Al, with an average grain size of 90.68 μm in the as-cast state. The grain size of the alloy is further reduced to 87.55 μm by the simultaneous addition of Y. The synergistic addition of Ce and Y changes the properties of the alloy. The addition of Ce and Y also produces the Al_(11)Ce_(3) and Al_(3)Y second phases, which have coherent relationship with a-Al. The two-dimensional mismatch degree was calculated to be only 4.43%and 0.85%, respectively, which can provide a certain amount of nucleation substrate for a-Al in the incubation stage. The interfacial match between the L1_(2)structure of Al_(3)Y and a-Al was calculated using first-principles simulations. The results indicate that Al_(3)Y has a strong bonding effect with a-Al. Nanoscale second phases at grain boundaries can be effective in reducing resistivity due to dislocation motion.Nanoscale second phases with better matching interfaces to the substrate have no positive effect on the scattering motion of electrons.

Effect of stress profile on microstructure evolution of cold-drawn commercially pure aluminum wire analyzed by finite element simulation

The evolution of microstructure in the drawing process of commercially pure aluminum wire （CPAW） does not only depend on the nature of materials, but also on the stress profile. In this study, the effect of stress profile on the texture evolution of the CPAW was systematically investigated by combining the numerical simulation and the microstructure observation. The results show that the tensile stress at the wire center promotes the formation of 〈111〉 texture, whereas the shear stress nearby the rim makes little contribution to the texture formation. Therefore, the 〈111 〉 texture at the wire center is stronger than that in the surface layer, which also results in a higher microhardness at the center of the CPAW under axial loading.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.

Design of pure aluminum laminates with heterostructures for extraordinary strength-ductility synergy

Heterogeneous metals and alloys are a new class of materials with superior mechanical properties.In this paper,we engineered sandwich-structured pure aluminum laminates composed of middle coarse-grained layer and outer fine-grained layer via extrusion,rolling and annealing.By controlling the post-annealing regimes,a larger degree of microstructure heterogeneities such as boundary spacing,misorientation and texture across the hetero-interface were obtained,which resulted in obvious mechanical differences.Tensile tests indicated that the 300℃/30 min annealed laminates enabled a relatively high tensile ductility while simultaneously retaining a high strength,which was better than prediction by the rule-of-mixture.To explain the reasons behind it,the evolution of geometrically necessary dislocations and strain gradient at the hetero-interface zone were detected using in-situ tension and microscopic digital image correlation technique.It was found that with the increasing applied strain,a significant strain gradient was developed near the interface,which was accommodated by geometrically necessary dislocations,thereby contributing to higher hetero-deformation induced(HDI)strengthening and hardening.

Effects of AlCoCrFeNiTi high-entropy alloy on microstructure and mechanical properties of pure aluminum

A new kind of AlCoCrFeNiTi high-entropy alloy(HEA)as a grain refiner was prepared by vacuum arc melting.In this work,the effects of HEA(1.0 wt.%,2.0 wt.%and 3.0 wt.%)on the microstructure and mechanical properties of pure aluminum were studied.The microstructure was characterized and examined by scanning electron microscope(SEM),energy dispersive X-ray spectroscopy(EDS),X-ray diffraction(XRD),electron probe micro-analyzer(EPMA)and transmission electron microscopy(TEM)to indicate the refining abilities and mechanism of HEA on pure aluminum.Results show that the addition of HEA refined both the macrostructure and microstructure of pure aluminum.When 1.0 wt.%HEA was added,most coarse columnar grains were refined into equiaxed crystals,and as the amount of HEA increased to 2.0 wt.%and3.0 wt.%,aluminum grains were further refined,and the grain boundaries were nearly indistinguishable.Moreover,the morphology ofα-Al transformed from coarse columnar crystals to equiaxed grains,and the mean size ofα-Al grains decreased from 374μm to 27μm.The Al3Ti,Al3Ni,and nano-phase precipitated from the aluminum alloy with HEA in the solidification.The typical rod-like nano-phases distributed interdendritic regions ofα-Al.The average length of nano-phases is 2568 nm,4372 nm,and 6907 nm and the average diameter is 112 nm,103 nm,and 92 nm when 1.0 wt.%,2.0 wt.%and 3.0 wt.%HEA were added to the pure aluminum,respectively.The ultimate tensile strength(UTS)and yield strength(YS)were improved in all samples,whereas the elongation(El)was decreased with increasing HEA concentration.When 3.0 wt.%HEA was added into the aluminum melt,the UTS was improved by 145.2%from62 MPa to 152 MPa,the YS was increased by 173.8%from 42 MPa to 115 MPa,and the El was decreased by 33.3%from 39%to 26%.

电压对纯铝板陶瓷膜层显微组织及其性能的影响

分别采用恒定电压和阶梯电压在纯铝板表面制备陶瓷膜层,研究不同电压模式对陶瓷膜层组织和性能的影响。借助扫描电子显微镜、X射线衍射仪、显微硬度计和电化学工作站等,研究纯铝板表面陶瓷膜层的微观形貌、物相、显微硬度和耐腐蚀性能,并分析陶瓷膜层形成机理。结果表明:纯铝板表面陶瓷膜层是非晶态Al2O3相,与恒定电压相比,采用阶梯电压制备的陶瓷膜层孔洞、裂纹等缺陷较少。恒定电压和阶梯电压为26 V时,陶瓷膜层显微硬度均达到最大,分别为520.2 HV和570.2 HV。阶梯电压为26 V时,陶瓷膜层耐腐蚀性能最佳,自腐蚀电位和极化电阻分别为-0.429 V和113173.9Ω。采用阶梯电压在纯铝板表面制备陶瓷膜层时,每次电压升高都会加速化学反应速率,在纯铝板表面生成致密均匀的内部阻挡层,从而提高陶瓷膜层的显微硬度和耐腐蚀性能。

2A12包铝薄板阳极氧化膜黑点原因分析及解决

[目的]2A12包铝薄板在硫酸阳极氧化及封闭后表面出现大量针尖状黑点。解决该问题对指导生产极其重要。[方法]先通过扫描电镜和能谱仪对比了黑点位置和正常区域阳极氧化膜及基体的形貌和元素组成,然后结合生产实际来分析黑点出现的原因,并进行验证试验,提出了控制膜层黑点的措施。[结果]2A12包铝薄板表面存在含碳夹杂物,对应部位在阳极氧化过程中不参与反应成膜。阳极氧化前用硝酸-氢氟酸处理2A12包铝薄板,黑点问题得以解决。[结论]原材料状态是影响包铝薄板硫酸阳极氧化的因素之一。因此除了控制好各工序的工艺参数外,还应对原材料的品质进行严格把控。