Effects of magnesium chloride-based multicomponent salts on atmospheric corrosion of aluminum alloy 2024

Atmospheric corrosion of aluminum alloy 2024 （AA2024） with salt lake water was simulated through a laboratory- accelerated test of cyclic wet-dry and electrochemical techniques. Effects of the soluble magnesium salt contained in the salt water were investigated by scanning electron microscope （SEM）, transmission electron microscope （TEM）, energy dispersive spectrometer （EDS）, electron probe micro analyzer （EPMA）, X-ray diffraction （XRD）, infrared transmission spectroscope （IR）, and atmospheric corrosion monitor （ACM）. The results showed that, with the deposition, atmospheric corrosion of AA2024 could occur when the relative humidity （RH） was lower than 30%. A main crystalline component of corrosion products, layered double hydroxides （LDH）, [Mg1-xAlx（OH）2]^x＋ Clx-·mH2O （LDH-C1）, was determined, which meant that magnesium ion played an important role in the corrosion process. It not only facilitated the corrosion as a result of deliquescence, but also was involved in the corrosion process as a reactant.

Microstructure evolution and mechanical properties of ultrasonic-assisted soldering joints of 2024 aluminum alloys

Ultrasonic-assisted soldering of 2024 aluminum alloys using a filler metal of Zn-5Al alloy was investigated at the temperature of 400 ℃,which is lower than the solution strengthening temperature of Al-Cu alloys.The ultrasonic vibration with power of 200 W and vibration amplitude of 15 μm at the frequency of 21 kHz was applied on the top samples.The ultrasonic vibration promoted the dissolution of Al elements in the base metal.The reduction of volume fraction of the eutectic phases in the bonds was investigated by increasing ultrasonic vibration time.As the ultrasonic vibration time increased from 3 s to 30 s,the volume fraction of the eutectic phase in the bonds decreased from 12.9% to 0.9%,and the shear strength of the joints was up to 149-153 MPa,increased by 20%.The improvement of the mechanical properties of joints was discussed based on the modulus and hardness of the phases in the bonds and the fracture of the joints.

Multi-axial Fatigue of 2024-T4 Aluminum Alloy

Only the fatigue initiation is considered by the safe-life design approach,while fatigue crack propagation is paid more attention by the damage tolerance approach.The reasonable fatigue design method and durability assessment standard should give these two phases equivalent concerns.To develop a unified model of fatigue initiation and crack propagation,a great deal of baseline fatigue properties of a material should be obtained by fatigue experiments.However,there is lack of thorough and comprehensive experiment study on the fatigue properties of 2024-T4 aluminum alloy,which is widely used as load-bearing components in aircraft industry.In this paper,strain-controlled uniaxial,torsion,and combined axial-torsion fatigue experiments are conducted on 2024-T4 aluminum alloy in ambient air.Fully reversed uniaxial and pure torsion experiments employ solid cylindrical specimens.Fatigue experiments under the fully reversed shear loading with a static axial stress,proportional axial-torsion loading,and 90°out-of-phase axial-torsion nonproportional loading are conducted by using thin-walled tubular specimens.The experimental results show that the mean stress has a significant influence on the fatigue strength of the material.A tensile mean stress decreases the fatigue life dramatically,while a compressive mean stress increases the fatigue life.The strain-life fatigue results obtained from the fully reversed uniaxial fatigue experiments can be represented by one smooth curve of a three-parameter equation.However,two fitting curves are needed for characterizing the results of the fully reversed pure torsion fatigue tests because of the existence of an obvious kink.The baseline fatigue properties of 2024-T4 aluminum alloy obtained from the fatigue experiments have applications for the fatigue design and safe assessment of engineering components.

Anodizing of 2024-T3 aluminum alloy in sulfuric-boric-phosphoric acids and its corrosion behavior

The corrosion resistance of 2024-T3 aluminum alloy was improved by anodizing treatment in a mixed electrolyte containing 10% sulfuric acid, 5% boric acid and 2% phosphoric acid. Electrochemical impedance spectroscopy （EIS） technique was used to study the corrosion behavior of the anodized alloy. Using Tafel plot and salt spray techniques, it is revealed that the anodizing treatment of 2024-T3 aluminum alloy in sulfuric-boric-phosphoric acids provides better corrosion resistance and durability in comparison with the anodizing treatment in phosphoric acid or sulfuric-boric acids. This electrolyte can be a suitable alternative for chromate baths which are generally used in the anodizing of aluminum alloys.

Microstructure characteristics and solidification behavior of wrought aluminum alloy 2024 rheo-diecast with self-inoculation method

One important problem in casting wrought aluminum alloys is the high tendency to the formation of hot tears in the solidification process.By using semi-solid metal(SSM) processing,the hot tearing tendency of alloys can be minimized during casting.In the present research,the semi-solid slurry of wrought aluminum alloy 2024 was firstly prepared with a novel self-inoculation method(SIM),and then the microstructure characteristics of the semi-solid slurry and the rheo-diecastings cast with the semi-solid slurry were investigated.The results indicate that finer and more uniform globular primary α-Al particles can be obtained when the semi-solid slurry are isothermally held for a short period within the semi-solid temperature range,and the primary α-Al particles without entrapped liquid are uniformly fine,globular grains in the rheo-diecastings.The holding temperature and time affect the solid fraction,particle size,and shape factor.After the semi-solid slurry is held at 625 ℃ for 3 min and 5 min,the optimal values for the average equivalent diameter are 70.80 μm and 74.15 μm,and for the shape factor are 1.32 and 1.42,respectively.The solidification process of the rheo-diecastings is composed of the following two distinct stages:primary solidification process and secondary solidification process.The secondary solidification process consists further of the following three stages:(1) direct growth of secondary primary(α 2) phase from the surface of the primary α-Al phase particles without re-nucleation,(2) independent nucleation and growth of α 3 phase from the residual liquid,and(3) eutectic reaction at the end.

2024铝合金自冲铆成形工艺参数对接头微动滑移的影响

以冲压速度和铆钉硬度为影响因子,基于数值模拟与静力学试验,探究了低延展性材料2024铝合金自冲铆接头机械内锁区在受载工况下的微动滑移、几何特征尺寸的变化规律。结合静力学试验设备和数字图像采集系统,对自冲铆接头机械内锁区域滑移过程实时图像进行了采集和分析。结果表明,冲压速度和铆钉硬度对接头的微动滑移有显著影响。随着冲压速度的增加,铆钉扩张直径逐渐增加,而受载工况下接头微动滑移量逐渐减小;随着铆钉硬度的增加,微动滑移量逐渐增大,而铆钉扩张直径依次减小。数值模拟与试验结果的变化规律一致,据此得出微动滑移量与铆钉扩张直径呈一定反比关系。

Numerical simulation for macrosegregation in direct-chill casting of 2024 aluminum alloy with an extended continuum mixture model

An extended continuum mixture model for macrosegregation is applied to predicting Cu and Mg segregation in large-size ingot of 2024 aluminum alloy during direct chill casting（DC）. A microsegregation model using the approximate phase diagram data was coupled with macroscopic transport equations for macrosegregation profiles. Then, the impacts of transport mechanisms on the formation of macrosegregation were discussed. It is found that copper and magnesium have a similar segregation configuration from the billet center to surface. Negative segregation is observed in the centerline and subsurface, whereas positive segregation is obtained in the surface and somewhat underestimated positive segregation in the middle radius. Further, the discrepancy between the predicted and experimental results was discussed in detail. The results show that the magnesium to some extent alleviates the copper segregation in ternary alloy, compared with that in binary alloy. The predicted results show good agreement with measured experimental data obtained from literatures.

合金化因素和凝固速率对2024铝合金铸态组织的影响

2024高强铝合金的铸态组织对其热加工性能及最终使用性能具有重要的影响。通过调控2024铝合金的Cu,Mg含量以及凝固速率,探究Cu/Mg质量比以及凝固速率对铸态组织的影响。结果表明:随着Cu/Mg比从2.1提高到4.1,合金中第二相种类没有发生变化,但Al_(2)CuMg含量逐渐下降,Al_(2)Cu和Al_(23)Cu(Fe,Mn)_(4)的含量逐渐升高。当凝固速率从0.2℃/s提高到2.4℃/s时,合金的晶粒尺寸明显细化,平均晶粒尺寸从293.0μm减小到77.0μm,枝晶变得发达,枝晶臂间距减小,并且第二相的尺寸变得细小且分布更加均匀,Al_(23)Cu(Fe,Mn)_(4)难溶相的含量明显降低。可以通过降低合金中Cu/Mg比和适当提高凝固速率来减少富铁难溶相的生成,从而改善合金的加工性能和力学性能。

临界变形量下2024铝合金板材在固溶过程中的晶粒粗化及力学性能

研究了2024铝合金板材晶粒粗化的临界变形量,探讨了预变形量对合金织构及力学性能的影响。结果表明,合金晶粒粗化预变形量为6%,未粗化晶粒尺寸为29μm,粗化晶粒尺寸可达2839μm。固溶时效后合金主要存在Cube{100}<001>、Goss{110}<001>、Brass{110}<112>、Copper{112}<111>和S{123}<634>织构,随着预变形量的增加,Copper{112}<111>织构向Cube{100}<001>织构转变,形成以Cube{100}<001>织构为主的再结晶织构。晶粒粗化后强度和塑性显著降低,预变形量为8%时比未预变形的屈服强度降低38 MPa,伸长率下降到16.36%。随预变形量的增加,断口特征由韧性断裂向解理断裂特征转变。

EFFECT OF LOW-FREQUENCY ELECTROMAGNETIC FIELD ON THE AS-CASTING MICROSTRUCTURES AND MECHANICAL PROPERTIES OF HDC 2024 ALUMINUM ALLOY

The influences of the low frequency electromagnetic field on the horizontal direct chill casting process were investigated experimentally. Ingots of 2024 aluminum alloy with a cross size of 40 mm× 200 mm were produced by the conventional horizontal chill casting process and low frequency electromagnetic horizontal chill casting processre- spectively. The as-cast structures and the mechanical property of the ingots were examined. The results showed that the low frequency electromagnetic field could sub- stantially refine the microstructures and pronouncedly reduce the macrosegregation in the horizontal direct chill casting process. Moreover, the surface quality of the ingot was prominently improved by the low frequency electromagnetic field. The fracture strength and elongation percentage of the ingot was increased with the low frequency electromagnetic field.

Tensile properties and microstructure of 2024 aluminum alloy subjected to the high magnetic field and external stress

In order to explore the dependence of plasticity of metallic material on a high magnetic held,the effects of the different magnetic induction intensities（H = 0 T,0.5 T,1 T,3 T,and 5 T） and pulses number（N = 0,10,20,30,40,and 50） on tensile strength（σ;） and elongation（δ） of 2024 aluminum alloy are investigated in the synchronous presences of a high magnetic held and external stress.The results show that the magnetic held exerts apparent and positive effects on the tensile properties of the alloy.Especially under the optimized condition of H;=1 T and N;=30,the σ;and 8 are 410 MPa and 17% that are enhanced by 9.3% and 30.8% respectively in comparison to those of the untreated sample.The synchronous increases of tensile properties are attributed to the magneto-plasticity effect on a quantum scale.That is,the magnetic held will accelerate the state conversion of radical pair generated between the dislocation and obstacles from singlet to the triplet state.The bonding energy between them is meanwhile lowered and the moving flexibility of dislocations will be enhanced.At H;= 1 T and N;= 30,the dislocation density is enhanced by 1.28 times.The relevant minimum grain size is 266.1 nm,which is reduced by 35.2%.The grain rehning is attributed to the dislocation accumulation and subsequent dynamic recrystallization.The（211） and（220） peak intensities are weakened.It is deduced that together with the recrystallization,the hne grains will transfer towards the slip plane and contribute to the slipping deformation.

Nonmechanical criteria proposed for prediction of hot tearing sensitivity in 2024 aluminum alloy

Two theoretical criteria represented by Katgerman, and Clyne and Davies for prognosticating hot tearing sensitivity were compared. Both unrefined and grain-refined samples of Al2024 alloy were solidified at various cooling rates ranging from 0.4 to 17.5 °C/s. Thermal analysis was used to detect dendrite coherency point and temperature of eutectic reaction. Curves of solid and liquid fractions were plotted based on Newtonian method to determine hot tearing susceptible areas. The experimental results show that the most susceptible zone in which hot tearing can occur in Al2024 is where Al_2CuMg intermetallic compound forms as a eutectic phase at last stage of mushy-state interval. Also, both criteria are in a good agreement with each other at high cooling rates used in direct-chill casting process while Clyne and Davies＇ model is more acceptable to determine hot tearing tendency from low to medium cooling rates.

Preparation of anodic films on 2024 aluminum alloy in boric acid-containing mixed electrolyte

The anodizing oxidation process on 2024 aluminum alloy was researched in the mixed electrolyte with the composition of 30 g/L boric acid, 2 g/L sulfosalicylic acid and 8 g/L phosphate. The results reveal that the pre-treatment and the composition of the mixed electrolyte have influence on the properties of the films and the anodizing oxidation process. Under the condition of controlled potential, the anodizing oxidation current—time response curve displays "saddle" shape. First, the current density reaches a peak value of 8-20 A/dm2 and then decreases rapidly, finally maintains at 1-2 A/dm2. The film prepared in the mixed electrolyte is of porous-type with 20 nm in pore size and 500 μm-2 in porosity. Compared with the conventional anodic film obtained in sulfuric acid, the pore wall of the porous layer prepared in this work is not continuous, which seems to be deposited by small spherical grains. This porous structure of the anodic film may result from the characteristics of the mixed electrolyte and the special anodizing oxidation process. The surface analysis displays that the anodic film is amorphous and composed of O, Al, C, P, S, Si and no copper element is detected.

Effects of KMnO_4 on microstructure and corrosion resistance of microarc oxidation coatings on 2024 aluminum alloy

Microarc oxidation （MAO） coatings were prepared on 2024 aluminum alloy in a Na2SiO3-KOH electrolyte with KNinO4 addition varying from 0 to 4 g/L. The microstructure and phases of the coatings were characterized by scanning electron microscopy （SEM） and X-ray diffractometry （XRD）, respectively. The corrosion resistance of MAO coatings was evaluated by electrochemical potentiodynamic polarization in 5% （mass fraction） NaCl solution. The results show that when KMnO4 is added into base electrolyte, the growth speed of oxide coatings is increased obviously. The main phase of oxide coatings is Al2O3, and the contents of MnO2 and MnEA104 phases are increased at the top of oxide coatings with increasing the concentration of KMnO4. The solute elements participate in forming the oxide coatings. When a proper concentration of KMnO4 （2.5 g/L） is added into the base solution, the micropores of the MAO coatings are small and compact, and the corrosion resistance of oxide coatings is increased largely.

Forces and Stresses During Friction Stir Joining of 2024 Aluminum Alloy

An attempt is made to measure three direction forces using octagonal ring dynamometer in the 2024 aluminum alloy friction stir joining(FSJ)process.A test is made to measure the specific area stress and stress distributions in the specific area of the workpiece are obtained.The workpiece stresses in the FSJ process are analyzed by numerical simulation method.It is found that,in the downward stage of the process,feed force and lateral force in the tool are small,almost zero,and the maximum axial force can reach 12.5kN.In the stable joining stage,the forces acting on the tool become stabilized.Compared with the low speed,high feed speed results in small feed force and small lateral force,but large feed force in the stable joining stage.The stresses in three directions of feed direction,direction that perpendicular to butt face and direction perpendicular to the surface are obtained.The simulation stress value of measure point is obtained.Test and numerical simulation can authenticate each other.Both experimental stress values and numerical simulation stress values are credible.

Electron beam welding of SiCp/2024 and 2219 aluminum alloy

SiCp/2024 matrix composites reinforced with SiC particles and 2219 aluminum alloy were joined via centered electron beam welding and deflection beam welding,respectively,and the microstructures and mechanical properties of these joints were investigated.The results revealed that SiC particle segregation was more likely during centered electron beam welding(than during deflection beam welding),and strong interface reactions led to the formation of many Al4C3 brittle intermetallic compounds.Moreover,the tensile strength of the joints was 104 MPa.The interface reaction was restrained via deflection electron beam welding,and only a few Al4C3 intermetallic compounds formed at the top of the joint and heat affected zone of SiCp/Al.Quasi-cleavage fracture occurred at the interface reaction layer of the base metal.Both methods yielded a hardness transition zone near the SiCp/2024 fusion zone,and the brittle intermetallic Al4C3compounds formed in this zone resulted in high hardness.

Deformation Behavior and Microstructure Evolution of AA2024-H18 Aluminum Alloy by Hot Forming with Synchronous Cooling Operations

Hot forming with synchronous cooling(HFSC)is a novel technique for heat-treatable,high-strength aluminum alloys,which allows the alloys to acquire good formability,negligible springback,rapid processing and better mechanical properties.However,the deformation behavior and microstructure evolution of the alloys during HFSC are complex and need to be studied due to the temperature and strain rate effects.Uniaxial tensile tests in a temperature range of 250—450℃and a strain rate range of 0.01—1 s-1 for AA2024-H18 aluminum alloy sheet are conducted with a Gleeble-3500 Thermal-Mechanical Simulation Tester.And based on metallography observation and analysis,AA2024-H18 aluminum alloy sheet in HSFC process exhibits hardening and dynamic recovery behaviors within the temperature range of 250—450 ℃.Strain rate shows different effects on ductility at different temperatures.Compared with traditional warm/hot forming methods,AA2024-H18 aluminum alloy achieves a better work-hardening result through HFSC operations,which promises an improved formability at elevated temperature and thus good mechanical properties of final part.After HSFC operations,the microstructure of the specimens is composed of elongated static recrystallization grain.

形变退火工艺对2024铝合金性能的影响

采用正交试验法研究了形变量、预回复温度、预回复时间、退火温度和退火时间5个因素对2024铝合金力学性能和腐蚀性能的影响。结果表明:各因素对材料性能的影响显著,其中对力学性能影响最大的因素为退火温度,对腐蚀性能影响最大和最小的因素分别为形变量和退火时间。通过正交优化得到的最佳形变退火工艺如下:形变量为80%,且在220℃温度下预回复120 min,320℃温度下退火10 min,此工艺下获得的合金具较好综合性能,样品显微硬度、抗拉强度、屈服强度、延伸率、腐蚀深度、R_(p)和I_(corr)分别为74.49 HV、217.17 MPa、185.84 MPa、13.53%、55.4μm、3885.6Ω·cm^(-2)和9.42E-06A·cm^(-2)。

Grain refining in weld metal using short-pulsed laser ablation during CW laser welding of 2024-T3 aluminum alloy

The 2024 aluminum alloy is used extensively in the aircraft and aerospace industries because of its excellent mechanical properties.However,the weldability of 2024 aluminum alloy is generally low because it contains a high number of solutes,such as copper(Cu),magnesium(Mg),and manganese(Mn),causing solidification cracking.If high speed welding of 2024 aluminum alloy without the use of filler is achieved,the applicability of 2024 aluminum alloys will expand.Grain refining is one of the methods used to prevent solidification cracking in weld metal,although it has never been achieved for high-speed laser welding of 2024 aluminum alloy without filler.Here,we propose a short-pulsed,laser-induced,grain-refining method during continuous wave laser welding without filler.Bead-on-plate welding was performed on a 2024-T3 aluminum alloy at a welding speed of 1 m min−1 with a single mode fiber laser at a wavelength of 1070 nm and power of 1 kW.Areas in and around the molten pool were irradiated with nanosecond laser pulses at a wavelength of 1064 nm,pulse width of 10 ns,and pulse energy of 430 mJ.The grain-refinement effect was confirmed when laser pulses were irradiated on the molten pool.The grain-refinement region was formed in a semicircular shape along the solid–liquid interface.Results of the vertical section indicate that the grain-refinement region reached a depth of 1 mm along the solid–liquid interface.The Vickers hardness test results demonstrated that the hardness increased as a result of grain refinement and that the progress of solidification cracking was suppressed in the grain refinement region.

Microstructure and mechanical properties of friction stir welded thin sheets of 2024-T4 aluminum alloy

Friction stir welding (FSW) is a new and promising welding processing that can produce low-cost and high-quality joints of aluminum alloys. 1 mm thick sheets of 2024-T4 aluminum alloys which are always used as building and decorating materials were welded by FSW. The microstructure and mechanical properties of friction stir welded 1 mm thick sheets of 2024-T4 aluminum alloy were studied. It was found that the thinner the 2024 aluminum alloy, the larger the FSW technological parameters field. The grains size of weld nugget zone (WNZ) is approximately 10 times smaller than that of the parent material, but the second phase in the material is not refined apparently in the welding. The FS welded joints have about 40% higher yield strength than the parent material, but the elongation of FS welded joints is under about 50% of the parent material. The electron backscattered diffraction (EBSD) results show that there are much more low angle boundaries (LAB) in WNZ than that in parent material, which indicates that FSW causes a number of sub-grain structures in WNZ, and this is also the reason of the increase of yield strength and Vickers hardness of the welded joint.