Investigation of friction stir processing effect on AA 2014-T6

This study is concerned with the effects of process parameters such as speed, feed, tilt angle, and tool profile on mechanical and microstructural properties of stir processed, solution treated, and artificially aged AA 2014-T6. The process was carried out with an input condition at rotational and traverse feeds of 600–1400 RPM and 30–90 mm/min, respectively. Five distinct shapes of the tool pin such as triangular, hexagonal, threaded, conical, and cylindrical have been selected to carry out the process with varied tilt angle of 1°–3°. In order to exemplify the status of processed materials, optical, scanning electron microscopy and Vickers hardness measurement along with grain analysis were performed on various regions of processed cross sections. According to the results, combination of processing speed and rotational speed affects the microstructure and associated grain size and average hardness of the processed region.     

60mm厚度6061-T6铝合金板搅拌摩擦焊接接头微观组织与力学性能

采用搅拌摩擦焊接方法对6061-T6铝合金板进行了60mm双面对接焊实验,研究了搅拌摩擦焊接接头的微观组织与力学性能,结果表明:焊缝区微观组织沿厚度方向发生了不同程度的改变,焊接接头强度达到218MPa,为母材强度的70％;焊接热循环引发的金属强化相“重固溶”和“过时效”是接头力学性能下降的重要原因,其中前进侧热机影响...     

Numerical simulation and experimental investigation on friction stir welding of 6061-T6 aluminum alloy

A modified three-dimensional model was established to simulate the friction stir welding of the 6061-T6 aluminum alloy. A detailed calculating method of the heat generation was proposed by taking account of the contact conditions between the tool and the work-piece. The results show that the heat mainly generated within the region close to the shoulder, the high temperature exists within the upper portion of the weld and decreases along the thickness direction. The strong material flow mainly occurs within the region around the tool and the material ahead of the tool sweeps toward the RS and finally deposits behind the tool. During this procedure the material is extruded to experience different shear orientations, and a defect-prone region exists in the region where material flow is weak. The temperature field and material flow behaviors predicted by the simulation method are in good agreement with the results obtained by the experiments.     

Multipass FSP on AA6063-T6 Al: Strategy to fabricate surface composites

Surface composites were fabricated on AA6063-T6 base metal using silicon carbide (SiC) reinforcement particles by friction stir processing (FSP). Influence of multiple FSP passes was investigated on the SiC particle distribution, processed zone dimensions, and microhardness of fabricated composites. The rotational speed, traverse speed, and tool tilt were kept constant and the numbers of passes were varied at 2, 4, 6, and 8. The particle distribution in processed zone was analyzed using OM and SEM, while microhardness were evaluated by Vickers indentation test. The results reveal that with increase in FSP passes there is increase in processed zone dimensions and elimination of defects such as agglomeration of particles and void. The microhardness of reinforced region was increased uniformly with increasing passes which is attributed to homogeneous distribution of reinforcement particles. The peak microhardness value of 81.9 Hv was obtained in sample which is processed with eight numbers of FSP passes. Processed zone indicates good bonding with the substrate and grain refinement.     

Microstructures and mechanical properties of Al/Al2O3 surface nano-composite layer produced by friction stir processing

In this study, a new processing technique, friction stir processing (FSP) was attempted to incorporate nano-sized Al₂O₃ into 6082 aluminum alloy to form particulate composite surface layer. Samples were subjected to various numbers of FSP passes from one to four, with and without Al₂O₃ powder. Microstructural observations were carried out by employing optical and scanning electron microscopy (SEM) of the cross sections both parallel and perpendicular to the tool traverse direction. Mechanical properties include microhardness and wear resistance, were evaluated in detail. The results show that the increasing in number of FSP passes causes a more uniform in distribution of nano-sized alumina particles. The microhardness of the surface improves by three times as compared to that of the as-received Al alloy. A significant improvement in wear resistance in the nano-composite surfaced Al is observed as compared to the as-received Al.     

Effect of friction stir welding on the microstructure and mechanical properties of AA 6063-T6 aluminum alloy

In this study, AA 6063-T6 alloy plates were joined via friction stir welding using three different pin geometries (i. e., helical threaded, pentagonal and triangular) under various process parameters of tool rotational speed and welding speed. The microstructures and mechanical properties of the various welded joints were investigated. Macro-structural observations revealed that kissing bonds occurred in the welded joints due to fractured oxide layers. X-ray diffraction analysis indicated that the stir zones of the welded joints exhibited phases of Al₈Fe₂Si, Al₅FeSi, and Mg₂Si. In the welded joints, processed using a helical threaded pin, no tunnel-type defect was detected to occur; specimens were fractured outside of the joint region during tensile tests, indicating that the kissing bonds formed in the stir zones did not cause any deterioration in tensile strength or ductility. The welded joints processed using a helical threaded, pentagonal and triangular pin at 500 min⁻¹ tool rotational speed and 80 mm min⁻¹ welding speed exhibited a ductile deformation behavior along with a tensile strength in the range of 153 MPa to 155 MPa.     

Synthesis,characterization and mechanical behavior of Al 3003 - TiO2 surface composites through friction stir processing

Aluminum 3003 alloy used in the gas turbine and aerospace applications possesses medium bearing capacity. This technical paper reports the fabrication of Al 3003 alloy/TiO₂ composites using friction stir processing. The weight fraction of reinforced TiO₂ particles is varied between 0% and 6% with the increment of 1.5% in sequence. The fabricated specimens have been characterized by optical microscopy (OM), Energy dispersive X-ray spectroscopy (EDAX), Field emission scanning electron microscopy (FESEM), X-ray Diffraction analysis (XRD) and electron backscattered diagram (EBSD). Composite weld zone has witnessed the homogeneous distribution of TiO₂ particles. The formation of such composite by reinforcement exhibits increase in the hardness and tensile strength of the weld. Corresponding strengthening mechanism is illustrated and correlated with the characterization studies. Fractography study shows brittle to ductile transformation with the addition of TiO₂ particles.     

Effect of processing parameters on quench sensitivity of an AA7050 sheet

Secondary precipitation takes place in alloy 7050 during slow quenching after solution and results in a significantly decreased content of Mg, Zn elements. Optical microscopy, transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD) study showed the distribution of Al₃Zr particles plays a vital role in quenching process. The equilibrium η phases mainly precipitate at Al₃Zr particles within the recrystallized grains and other high energy areas (primarily grain boundaries). The influence of the processing (homogenization, hot rolling and solution) parameter on the quench sensitivity is also investigated by mechanical property examination (T6 temper). A ramping heat homogenization, controlled hot rolling (67% rolling reduction and 3-5 s⁻¹ deformation rate) and two-stage solution treatment result in lesser recrystallization and fewer high angle grain boundaries, and lower the boundary angles within sub-structures. The decreasing number of heterogeneous precipitation sites endows the study alloy with good quenching sensitivity and better mechanical properties.     

Different reinforcement strategies of hybrid surface composite AA6061/(B4C+MoS2) produced by friction stir processing

Aluminum surface composites have gained huge importance in material processing due to their noble tribological characteristics. The reinforcement of solid lubricant particles with hard ceramics further enriches the tribological characteristics of surface composites. In the current study, friction stir processing was chosen to synthesize hybrid surface composites of aluminum containing B₄C and MoS₂ particles with anticipated improved tribological behavior. B₄C and MoS₂ powder particles in 87.5: 12.5 ratio were reinforced into the AA6061 by hole and groove method. Microstructural observations indicated that reinforcement particles are well distributed in the matrix. The hardness and wear resistance of hybrid surface composites improved as compared to the base material, due to well distributed abrasive B₄C and solid lubricant MoS₂ particles in AA6061. The hybrid surface composites achieved ∼32 % increased average hardness as compared to the base material. Hole method revealed ∼13 % better wear resistance compared to the groove method for friction stir processed hybrid surface composite, attributing to an improved homogeneity of particle distribution shown by zigzag hole pattern. Moreover, friction stir processed AA6061 without reinforcement particles exhibited reduced hardness and wear resistance due to loss of strengthening precipitates during multi-pass friction stir processing.     

Al2O3 thin coating of AA 6082 T6 components using a fast regime fluidized bed

Fluidized bed processing is a relatively novel method for coating metal substrates. A detailed study was carried out into surface property and in micro-structure changes induced by fluidized bed processing. In particular, fluidized bed processing of AA 6082 T6 aluminum alloy components using alumina Al₂O₃ powder was investigated. Firstly, the build up of Al₂O₃ films was studied and characterized in terms of coating thickness and adhesion. It was found that trends of deposited Al₂O₃ were consistent with fluidized bed processing time. Secondly, the effect of fluidized bed treatment on surface properties of processed components was examined. Surface morphology was significantly affected and its evolution according to processing time was accounted for. Both compressive residual stresses and increased dislocation density were induced by treatment of external layers of samples, and significant hardening was also detected. Lastly, the ability of fluidized bed processing was tested on ‘ad hoc' fatigue samples. Rupture of fluidized bed treated samples as well as untreated samples was also discussed. At any rate, the fatigue behavior of processed components significantly improved. This quite new and unprecedented result is ascribed to the compressive residual stresses and work hardening induced by FB treatment in the outermost surface layers of the aluminum alloy.     

Deformation behaviour and microstructure of a 20% Al2O3 reinforced 6061 Al composite

Deformation and microstructural behaviours of a 20% (volume percent) particle reinforced 6061 Al matrix composite have been studied by torsion from 25 to 540°C with strain rates of 0.1, 1 and 5 s⁻¹. The logarithmic stress versus reciprocal temperature relationship exhibits two slopes indicating different deformation mechanisms. The 20% Al₂O₃/6061 Al composite shows a greater hardening behaviour than those of the 10% Al₂O₃/6061 Al composite and of the monolithic alloy. Above 250°C, TEM investigations reveal much smaller subgrain size and higher volume of non-cellular substructures, as well as dynamic recrystallization nuclei in the 20% Al₂O₃/6061 Al composite in comparison to those of the 10% Al₂O₃/6061 Al composite and matrix alloy the same test condition. The torsion fracture surface was studied and compared to the three point bending failure specimens.     

Impurity and surface condition effects on pore formation at Al2O3/FeAl interfaces

Abstract

Interfacial pores are commonly observed at the scale/alloy interface in NiAl and FeAl alloys after high temperature oxidation. The pores are often an order of magnitude larger than the oxide grains, and many are formed during the initial stage of oxidation. In order to better understand the development of these pores, the effects of pre-oxidation surface condition and surface impurities on pore formation at the oxide/alloy interface in Fe–40at%Al are investigated. Surface conditions included polishing to 4000 grit with SiC and polishing to 1 µm with diamond suspension. Surface impurities included a number of nitrate salts dissolved in water. Pore number distribution in each case was determined and related to the treatment effects. Testing was also performed on an Hf-containing Fe–40Al to evaluate the effect of adding a reactive element. It was found that surface roughness and the presence of impurities, even residues from water drops, increased the number of interfacial pores. Hf addition made the alloy more resistant to pore formation, but large pores developed under heavy salt deposits.     

Effect of leakage current and dielectric constant on single and double layer oxides in MOS structure

MOS structure of Al/Al₂O₃/n-Si, Al/TiO₂/n-Si and Al/Al₂O₃/TiO₂/n-Si was obtained by deposition of Al₂O₃ and TiO₂ on silicon substrate by RF Magnetron Sputtering system. The total thickness of the oxide layer ~ 40 ± 5 nm in the MOS structure was kept constant. Samples were characterized by X-Ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), Impedance analyzer and Current-voltage (J-V) characteristics. The variations in the dielectric constant and tan δ of the MOS capacitor in the frequency range of 1000Hz-1MHz were measured by impedance analyzer. The variation in dielectric constant of the Al/Al₂O₃/TiO₂/n-Si multilayer compared to single layer of Al/Al₂O₃/n-Si and Al/TiO₂/n-Si is due to high probability of defects, lattice mismatch and interface interactions. The steep rise of Tan δ values in the Al/Al₂O₃/TiO₂/n-Si structure is due to the resonance effect of both Al₂O₃ and TiO₂ layers. The leakage current mechanisms of MOS structures were extracted from Schottky coefficient and Poole-Frenkel coefficient. Theoretical values of Schottky coefficients (β_SC) and Poole-Frenkel coefficients (β_PF) for each sample were estimated using the real part of the dielectric constant. The experimental values were calculated from J-V characteristics and compared with theoretical values. The appropriate model has been proposed. It was found that Schottky and Poole-Frenkel mechanisms are applicable at low and high field respectively for all MOS structures. The combination of Al/Al₂O₃/TiO₂/n-Si is found to be a promising structure with high dielectric constant and low leakage current suitable for MOS devices.     

Study and improvement of interfacial properties in a MIS structure based on p-type InP

Indium phosphide is one of the most promising candidates among the available III-V semiconducting compounds for the development of MIS technology. This is based on the availability of InP substrates and the relatively large band gap. Before the deposition of the insulator, the InP surface must be treated and well passivated (Surf Interface Anal 20 (1993) 803; J Appl Phys 67 (1990) 4173). We have shown that a InSb buffer layer can reduce the phosphorus atom migration and the concentration of defects at the interface. We have studied and characterized electrically two series of substrates using p-type InP, the first one with thin and the second with thick insulator films. The results obtained show clearly the reduction of the defects in the thicker structures protected by the InSb buffer layer.     

Influence of excitation wavelengths on luminescent properties of Sr3Al2O6:Eu, Dy phosphors prepared by sol-gel-combustion processing

Eu²⁺ and Dy³⁺ ion co-doped Sr₃Al₂O₆ red-emitting long afterglow phosphor was synthesized by sol-gel-combustion methods using Sr(NO₃)₂, Al(NO₃)₃·9H₂O, Eu₂O₃, Dy₂O₃, H₃BO₃ and C₆H₈O₇·H₂O as raw materials. The crystalline structure of the phosphors were characterized by X-ray diffraction, luminescent properties of phosphors were analyzed by fluorescence spectrophotometer. The effect of excitation wavelengths on the luminescent properties of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors was discussed. The emission peak of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor lays at 516 nm under the excitation of 360 nm, and at 612 nm under the excitation of 468 nm. The results reveal that the Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor will emit a yellow-green light upon UV illumination, and a bright red light upon visible light illumination. The emission mechanism was discussed according to the effect of nephelauxetic and crystal field on the 4f⁶5d¹ → 4f⁷ transition of the Eu²⁺ ions in Sr₃Al₂O₆. The afterglow time of (Sr_0.94Eu_0.03Dy_0.03)₃ Al₂O₆ phosphors lasts for over 600s after the excited source was cut off.     

Al2O3/6-6-3青铜复合材料的制备及性能

采用粉末冶金法制备出Al₂O₃/青铜复合材料, 研究了烧结温度、Al₂O₃颗粒尺寸、含量及表面状态对复合材料性能的影响。结果表明, 采用二次压制与烧结工艺制备的复合材料的组织致密,Al₂O₃颗粒分布均匀, 综合性能优于6-6-3青铜材料。Al₂O₃颗粒的化学包覆处理可以使复合材料的性能进一步提高。      

Utilization of Chemically Synthesized Fine Powders of SiC/Al2O3 Composites for Sintering

Fine powders of (Al₂O₃)_100–x(SiC)_x (0 ≤ x ≤ 50) composites were prepared by chemical route (named as pyrophoric technique) to achieve a uniform mixture of SiC in an alumina matrix. The chemically synthesized fine SiC/Al₂O₃ composite powders were sintered to form composites at 1450°C which is well below the sintering temperature of SiC. Sintering was performed in an argon atmosphere. Highly dense SiC/Al₂O₃ microstructures were achieved. An improvement in bulk density and hardness has been achieved for SiC/Al₂O₃ composites with 20 wt% of SiC. Hexagonal-shaped grains have been obtained in (Al₂O₃)₅₀(SiC)₅₀ composite with well-connected grain boundaries. The peak position of alumina in SiC/Al₂O₃ composites shifts toward lower wavenumbers in Fourier transform infrared spectroscopy and higher wavenumbers in Raman spectroscopy due to the incorporation of SiC in the composites. The optical band gap decreases with the addition of SiC and the composite behaves more like a semiconductor rather than an insulator. These properties make SiC/Al₂O₃ composites attractive for various industrial applications.     

Influence of calcination temperature on luminescent properties of Sr3Al2O6:Eu, Dy phosphors prepared by sol–gel-combustion processing

The detailed preparation process of Eu²⁺ and Dy³⁺ ion co-doped Sr₃Al₂O₆ phosphor powders with red long afterglow by sol–gel-combustion method in the reducing atmosphere is reported. X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy are used to investigate the effects of synthesis temperature on the crystal characteristics, morphology and luminescent properties of the as-synthesized Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors. The results reveal that Sr₃Al₂O₆ crystallizes completely when the combustion ash is sintered at 1200 °C. The excitation and the emission spectra indicate that the excitation broad-band lies chiefly in visible range and the phosphor powders emit strong light at 618 nm under the excitation of 472 nm. The light intensity and the light-lasting time of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors are increased when increasing the calcination temperatures from 1050 to 1200 °C. The afterglow of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors sintered at 1200 °C lasts for over 600 s when the excited source is cut off. The red emission mechanism is discussed according to the effect of nephelauxetic and crystal field on the 4f⁶5d¹ → 4f⁷ transition of the Eu²⁺ ions.     

Vickers Indentation Fracture (VIF) modeling to analyze multi-cracking toughness of titania, alumina and zirconia plasma sprayed coatings

For massive brittle materials, the fracture toughness in mode I, K_IC, can be determined using various reliable techniques. Besides, Vickers Indentation Fracture (VIF) technique has been developed to locally determine fracture toughness. However, since the indentation test generates a complex three-dimensional crack system around the indent, fracture toughness, K_C, is calculated instead of K_IC. Consequently some authors rightly reject the VIF technique to determine standard fracture toughness by arguing that the literature counts numerous VIF crack equations thus revealing discrepancies of this technique. Nevertheless in some cases (e.g. brittle ceramic coatings) inclusive material techniques are not applicable since presence of the substrate and/or multi-crack network can modify the crack propagation into the coating.In this work, we employed VIF technique to study multi-cracking behavior of titania, alumina and zirconia ceramic oxide coatings obtained by plasma spraying. To calculate VIF toughness, we propose (i) to select two crack equations for radial-median and Palmqvist cracking modes respectively, (ii) to adjust the crack equation of Miranzo and Moya for intermediate cracking mode, (iii) to develop a mathematical approach to determine the cracking mode, (iv) to take into account the multi-crack network by defining an equivalent four-crack system and (v) to propose a universal crack equation applicable independently of the cracking mode.     

单磨粒作用下Al2O3-TiC-TiN复合陶瓷的摩擦磨损特性

本文利用置于扫描电子显微镜（SEM）中的销-盘（pin－disk）式滑动摩擦磨损试验装置，研究了在单颗粒磨粒的作用下Al₂O₃－TiC－TiN复合陶瓷的摩擦磨损特性．结果显示，在真空和空气两种环境中，该材料的摩擦行为具有不同的特点．其磨损机理，在磨损初期表现为明显的微切削，随着磨损的进行，其机理以脆性的微断裂为主．同时还表明，在三体磨粒磨损条件下，磨粒的相对软硬显著地影响该陶瓷的磨损率．