搅拌摩擦加工原位反应制备Al3Ti-Al表面复合层

通过在铝合金1100-H14表面加工矩形凹槽并添加微米级钛粉再进行搅拌摩擦加工(friction stir processing,FSP)的方法,在铝合金表面获得Al3Ti-Al复合层.采用扫描电镜(SEM),能谱分析(EDS)以及X射线衍射(XRD)对表面复合层微观结构及相组成进行了分析,并对复合层的显微硬度进行了检测.结果表明,在FSP强烈的热、力耦合作用下,钛粉产生了碎化,破碎后的钛颗粒与铝产生快速原位反应,生成微米和亚微米级Al3Ti颗粒,残留的钛颗粒和细小的Al3Ti颗粒一同均匀地分布于铝合金基体中,从而使得铝合金表面的硬度得到提高,其平均值达到了71.39HV,为基体硬度的2.1倍.     

搅拌摩擦加工制备纳米RE/Al2O3增强铝基复合材料

铝基复合材料因其优异的物理性能及机械性能已得到广泛应用.文中通过在2219-O铝合金内部添加不同比例的RE/Al₂O₃纳米粉末,利用搅拌摩擦加工技术,制备铝基复合材料.并对搅拌区进行金相、拉伸、硬度、SEM,EDS和XRD等试验.结果表明,搅拌区金属在搅拌头强烈的搅拌摩擦作用下发生显著的塑性变形和连续动态再结晶,形成细小的等轴晶粒,并具有明显的洋葱环组织.复合材料的抗拉强度为母材的163%、屈服强度为母材的195%,同时硬度也明显增加.但是不同稀土比例对金属基复合材料的组织形貌和力学性能影响不大.大块复合材料制备过程粉末添加及隧道型缺陷的控制是关键.     

Functionally graded materials produced by friction stir processing

An investigation was conducted in order to produce aluminium based functionally graded MMC reinforced by SiC ceramic particles with median size of 118.8, 37.4 and 12.3 μm. AA5083 aluminium alloy plates in the H111 and partially annealed conditions were processed. Several strategies for reinforcement were investigated and its influence on the particle distribution and homogeneity was studied. A square shaped groove packed with reinforcement particles of SiC was studied and it was seen that it was more effective when the groove was placed under the probe. If the groove was placed outside the probe interaction area, but within the shoulder influence area, insufficient dispersion of particles was observed. Small particles lead to higher concentration along the bead surface and to smooth fraction gradients both in depth and along the direction parallel to the surface. The thickness of the reinforced layer depends of particle size within the parametric conditions and the tool geometry used in this investigation.     

搅拌摩擦加工Al-Pb表面复合材料的微结构和织构

采用搅拌摩擦加工(FSP)方法制备Al-Pb表面复合材料,以提高其减摩抗磨性能,使用SEM、EBSD、纳米压痕仪和显微硬度计等分析其微观组织、织构和硬度分布。结果表明:使用FSP方法制备Al-Pb表面复合材料,Pb颗粒受到重力和搅拌作用,主要分布于盆状搅拌加工区的底部。塑性金属对流形成的洋葱环结构中,存在富Pb片层和形变铝基体片层。富Pb片层内的Pb颗粒,起到了良好的细化晶粒作用。形变铝基体片层分布有少量直径约100 nm的新生Pb粒。受到细晶强化作用影响,富Pb颗粒区的硬度显著高于形变铝基体。加工区底部的SZ-AS区形成强Cube再结晶织构;SZ-RS区形成Cube织构和少量Brass织构;CSZ区的Cube织构较少,{111}织构增强;上部的AS区形成强Goss织构,RS区织构相对随机。     

Reinforcement strategies for producing functionally graded materials by friction stir processing in aluminium alloys

The present work addresses the production of aluminium based FGM composites by friction based processes, namely FSP and a consumable tool approach. Several strategies were investigated, featuring the use of SiC and alumina reinforcements. These strategies were implemented and surfaces analyzed to evaluate the influence of deposition and processing on particle distribution and homogeneity. Three strategies were studied: a square shaped groove packed with reinforcement particles, the pre-deposition of a uniform layer of particles prior to FSP with a non consumable tool, and the last one consisted of a consumable rod in aluminium drilled with holes placed in different positions along a radial line filled with reinforcing particles. Coatings were examined by optical microscopy, scanning electron microscopy, as well as, hardness testing. The strategies investigated proved to be possible in the production of surface layers reinforced with hard materials by FSP in aluminium based alloys. While the pre-deposition of reinforcements directly on plate surface enables the simplest approach to produce composites by FSP, the packing of reinforcements in grooves can increase the composite layer thickness. The consumable rod approach allows depositing composite layers soundly bonded to the substrate while avoiding FSP tool wear.     

Surface modification of aluminium by friction stir processing

In this study, SiC particles were incorporated by using Friction Stir Processing (FSP), into the commercially pure aluminium to form particulate surface layers. Samples were subjected to the various tool rotating and traverse rates with and without SiC powders. Microstructural observations were carried out by employing optical microscopy of the modified surfaces. Mechanical properties like hardness and plate bending were also evaluated. The results showed that increasing rotating and traverse rate caused a more uniform distribution of SiC particles. The hardness of produced composite surfaces was improved by three times as compared to that of base aluminium. Bending strength of the produced metal matrix composite was significantly higher than processed plain specimen and untreated base metal.     

Development of ceramic backing for friction stir welding and processing

Usually, a workpiece is deformed during friction stir welding due to high applied loads. Consequently, fully and consolidated friction stir-welded joints as well as tool life time can be affected promoting unscheduled manufacturing stops, which favour decreasing the welding productivity. Furthermore, the workforce is dislocated to not predicted maintenance steps. This work proposes the development of a special ceramic backing to joining and processing material using FSW technologies. Four ceramic deposits were tested over a steel plate, which allowed selecting those with less porosity and, thus, better strength. This backing allowed us to obtain full penetration welds for duplex stainless steels, to high forces during engagement for high-strength low-alloy steels and to obtain consolidated aluminium–steel dissimilar joints. For the last one, there was not adherence of the soft material in the workpiece. In addition, the ceramic backing allowed us to confine the heat and plasticized metal, as well as develop established welding parameters.     

La2O3含量对搅拌摩擦加工制备Ni /Al复合材料组织和性能的影响

采用搅拌摩擦加工方法在Al基体中添加不同La₂O₃含量的混合粉末(Ni+La₂O₃),制备 (Ni+La₂O₃)/Al复合材料。采用SEM、EDS、 EPMA及XRD对复合区微观结构及相组成进行分析,采用室温拉伸试验对 (Ni+La₂O₃)/Al复合材料力学性能进行了测试。结果表明,随着La₂O₃含量的增加,(Ni+La₂O₃)/Al复合材料的组织和性能先变好后变差。当La₂O₃添加量达到5%时,复合材料中Al₃Ni增强颗粒分布均匀、颗粒数量最多,块状的Ni粉团聚减少,其抗拉强度达到最大值215MPa,相比Ni/Al复合材料(抗拉强度176MPa),其抗拉强度提高了22%;当La₂O₃的添加量为7%时,复合材料中Al₃Ni增强颗粒含量减少,块状Ni粉团聚重新出现,抗拉强度下降至201MPa。     

Fabrication of Al/Al2Cu in situ nanocomposite via friction stir processing

The aim of present work is fabrication of Al/Al₂Cu in situ nanocomposite by friction stir processing (FSP) as well as investigation of FPS parameters such as rotational speed, travel speed, number of FSP passes, and pin profile on the microstructure, chemical reaction, and microhardness of Al based nanocomposite. The Al₂Cu particles were formed rapidly due to mechanically activated effect of FSP as well as high heat generation due to Al-Cu exothermic reaction. The microstructure of the nanocomposites consisted of a finer grained aluminium matrix (～15 µm), unreacted Cu nanoparticles (～40 nm), and reinforcement nanoparticles of Al₂Cu. Irregular morphology of Al₂Cu is attributed to the local melting during FSP. Pin diameter has a higher effect on the microstructure and hardness values. The hardness measurements exhibited enhancement by 57% compared with the base metal.     

Microstructure and wear performance of Al5083/CeO2/SiC mono and hybrid surface composites fabricated by friction stir processing

Friction stir processing (FSP) was utilized to produce surface composites by incorporating nano-sized cerium oxide (CeO₂) and silicon carbide (SiC) particles individually and in combined form into the Al5083 alloy matrix. The study signified the role of these reinforcements on microstructure and wear behavior of the resultant surface composite layers. The wear characteristics of the resultant mono and hybrid surface composite layers were investigated using a pin-on-disc wear tester at room temperature. The microstructural observations of FSPed regions and the worn out surfaces were performed by optical and scanning electron microscopy. Considerable grain refinement and uniform distribution of reinforcement particles were achieved inside the nugget zone. All the composite samples showed higher hardness and wear resistance compared to the base metal. Among the composite samples, the hybrid composite (Al5083/CeO₂/SiC) revealed the highest wear resistance and the lowest friction coefficient, whereas the Al5083/SiC composite exhibited the highest hardness, i.e., 1.5 times as hard as that of the Al5083 base metal. The enhancement in wear behavior of the hybrid composites was attributed to the solid lubrication effect provided by CeO₂ particles. The predominant wear mechanism was identified as severe adhesive in non-composite samples, which changed to abrasive wear and delamination in the presence of reinforcing particles.     

Microstructural and mechanical properties of Al-Mg/Al2O3 nanocomposite prepared by mechanical alloying

The effect of milling time on the microstructure and mechanical properties of Al and Al-10 wt.% Mg matrix nanocomposites reinforced with 5 wt.% Al₂O₃ during mechanical alloying was investigated. Steady-state situation was occurred in Al-10Mg/5Al₂O₃ nanocomposite after 20 h, due to solution of Mg into Al matrix, while the situation was not observed in Al/5Al₂O₃ nanocomposite at the same time. For the binary Al-Mg matrix, after 10 h, the predominant phase was an Al-Mg solid solution with an average crystallite size 34 nm. Up to 10 h, the lattice strain increased to about 0.4 and 0.66% for Al and Al-Mg matrix, respectively. The increasing of lattice parameter due to dissolution of Mg atom into Al lattice during milling was significant. By milling for 10 h the dramatic increase in microhardness (155 HV) for Al-Mg matrix nanocomposite was caused by grain refinement and solid solution formation. From 10 to 20 h, slower rate of increasing in microhardness may be attributed to the completion of alloying process, and dynamic and static recovery of powders.     

Modification of thermally sprayed cemented carbide layer by friction stir processing

The modification of a thermally sprayed cemented carbide (WC-CrC-Ni) layer by friction stir processing (FSP) was studied. The cemented carbide layer was successfully modified using a sintered cemented carbide (WC-Co) tool. The defects in the cemented carbide layer disappeared and the hardness of the cemented carbide layer increased to ∼ 2000 HV, which was about 1.5 times higher than that of the as-sprayed cemented carbide layer. Additionally, the cemented carbide layer was bonded to the SKD61 (Nominal composition: 0.35-0.42 mass% C, 0.8-1.2 mass% Si, 0.25-0.5 mass% Mn, 4.8-5.5 mass% Cr, 1.0-1.5 mass% Mo, 0.8-1.2 mass% V, balance Fe) substrate by diffusion of the metallic elements and the distortion of the coating-substrate interface producing a mechanical interlocking effect.     

《搅拌摩擦加工制备GNPs/Al复合材料的微观结构与力学性能》

本文以纯铝为基体,利用搅拌摩擦加工(FSP)制备GNPs/Al复合材料,研究了复合材料基体组织、增强相与界面等微观结构与力学性能,探讨了其增强机理。结果表明,添加GNPs并经FSP后复合材料基体晶粒得到明显细化且晶界由小角度为主转变为大角度为主;FSP制备过程致使GNPs片层一定程度剥离的同时,较大片径的GNPs被破碎而形成众多边缘缺陷,使其易发生Al-C原子扩散,结果在GNPs边缘与基体形成界面过渡;GNPs加入量约1.8vol%时,复合材料的屈服强度和抗拉强度达到72MPa和147MPa,较同等条件FSP的基体分别提高了89.5%和79.3%,理论计算界面载荷传递、Orowan和细晶强化依次是复合材料的主要增强机制;随着GNPs加入量的增加,复合材料屈服强度实验值与理论值的增长趋势一致,且偏差也略有提高,但可能因GNPs在复合材料中的杂乱排布,界面载荷传递强化不能充分发挥,实际的复合材料屈服强度与理论值尚有差距。     

Enhanced mechanical properties of Mg-Gd-Y-Zr casting via friction stir processing

Mg-10Gd-3Y-0.5Zr casting was subjected to friction stir processing (FSP) at a tool rotation rate of 800 rpm and a traverse speed of 50 mm/min. FSP resulted in the fundamental dissolution of the coarse network-like β-Mg₅(Gd,Y) phase and remarkable grain refinement (∼6.1 μm), thereby significantly improving the strength and ductility of the casting. Post-FSP aging resulted in the precipitation of fine β′′ and β′ particles in a fine-grained magnesium matrix, producing an ultimate tensile strength of 439 MPa and a yield strength of 330 MPa. FSP combined with aging is a simple and effective approach to enhancing the mechanical properties of Mg-Gd-Y-Zr casting.     

Microstructure and magnetic properties of Co/Al2O3 nanocomposite powders

Nanocomposite powders of magnetic cobalt nanoparticles dispersed by nonmagnetic Al₂O₃ particles have been prepared by planetary ball milling. Ball milling of the CoO and Al mixture powder after a certain milling duration reduces CoO to (fcc and hcp) Co completely and oxidizes Al to -Al₂O₃ simultaneously. The average grain sizes of the nanocomposite powders are 19 nm for Co and 28 nm for -Al₂O₃ after the completion of the reduction reaction. By direct ball milling of the mixture of Co and Al₂O₃, the allotropic phase transformation of Co was observed and the average grain size of Co is reduced to 5 nm. For both the samples of the mechanochemical series and the direct milling series, the saturation magnetizations of the nanocomposite powders decrease with decreasing average grain size of Co. This may be due to the enhancement of the interface effects and the increase of the superparamagnetic particles with decreasing Co grain size. The coercivities of the Co/Al₂O₃ nanocomposite powders increase up to 380 Oe. The increasing grain boundaries with decreasing Co grain size result in the domain wall pinning which predicts the coercivity enhancement. In addition to the grain size effects, the reduction of the particle size toward the size region of single domain also contributes to the increase of coercivity.     

搅拌摩擦加工制备镁基铝覆层材料的组织与性能

在采用多道次搅拌摩擦加工成功地在镁合金表面覆合一层铝层的基础上,利用光学显微镜、透射电子显微镜、扫描电子显微镜、能谱分析和电子万能材料试验机对界面组织、元素成分分布、界面结合力和断口形貌进行了分析,并分析了不同焊接速度对重叠区界面组织和性能的影响规律.结果表明,界面由N道次区、重叠区和N+1道次区组成,重叠区界面过渡层的厚度随着焊接速度的降低而增加.其过渡层由Al+Al₃Mg₂相和Mg+Al₁₂Mg₁₇相组成.重叠区界面的剪切力随着速度的降低而增加,断裂方式为塑性断裂.     

Fabrication of A356 composite reinforced with micro and nano Al2O3 particles by a developed compocasting method and study of its properties

Aluminum/alumina composites are used in automotive and aerospace industries due to their low density and good mechanical strength. In this study, compocasting was used to fabricate aluminum-matrix composite reinforced with micro and nano-alumina particles. Different weight fractions of micro (3, 5 and 7.5 wt.%) and nano (1, 2, 3 and 4 wt.%) alumina particles were injected by argon gas into the semi-solid state A356 aluminum alloy and stirred by a mechanical stirrer with different speeds of 200, 300 and 450 rpm. The microstructure of the composite samples was investigated by Optical and Scanning Electron Microscopy. Also, density and hardness variation of micro and nano composites were measured. The microstructure study results revealed that application of compocasting process led to a transformation of a dendritic to a nondendritic structure of the matrix alloy. The SEM micrographs revealed that Al₂O₃ nano particles were surrounded by silicon eutectic and inclined to move toward inter-dendritic regions. They were dispersed uniformly in the matrix when 1, 2 and 3 wt.% nano Al₂O₃ or 3 and 5 wt.% micro Al₂O₃ was added, while, further increase in Al₂O₃ (4 wt.% nano Al₂O₃ and 7.5 wt.% micro Al₂O₃) led to agglomeration. The density measurements showed that the amount of porosity in the composites increased with increasing weight fraction and speed of stirring and decreasing particle size. The hardness results indicated that the hardness of the composites increased with decreasing size and increasing weight fraction of particles.     

Formation of Al2O3-Bi4Ti3O12 nanocomposite oxide films on low-voltage etched aluminum foil by sol-gel processing

A water-based bismuth titanate Bi₄Ti₃O₁₂ (BTO) sol was synthesized by mixing bismuth nitrate, tetra-n-butyl titanate, lactic acid, acetic acid and distilled water. The sol was applied to low-voltage etched aluminum foil by dip-coating. The crystallization process of Bi₄Ti₃O₁₂ on low-voltage etched aluminum foil was measured by thermal gravimetry-differential scanning calorimetry (TG-DSC) and high-temperature X-ray diffraction (HT-XRD). It was found that Bi₄Ti₃O₁₂ sol first converted into intermediate phase Bi_1.74Ti₂O_6.624, then transformed into perovskite phase Bi₄Ti₃O₁₂. After annealed at 600 °C for 30 min in air, the low-voltage etched aluminum foil covered with Bi₄Ti₃O₁₂ sol was anodized galvanostatically in 15 wt.% ammonium adipate solution. The voltage-time variation during anodizing was monitored and recorded. The structure and composition of samples were investigated by field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDAX). Results showed that the anodic composite oxide film was composed of an inner Al₂O₃ layer and an outer Bi₄Ti₃O₁₂ layer. The specific capacitance and the product of specific capacitance and withstanding voltage of samples with a BTO coating were about 56.64% and 43.77% larger than that without a BTO coating.     

Friction stir processing of Al/SiC composites fabricated by powder metallurgy

Friction stir processing (FSP) was applied to modify the microstructure of sintered Al–SiC composites with particle concentrations ranging from 4 to 16 vol%. Two SiC particle sizes (490N and 800 grades) were examined. Following FSP, the hardness of the 4 and 8 vol% of 490N grade SiC composites increased from 130 HV and 145 HV to 171 HV and 177 HV respectively. The increase was accounted for by the severe deformation occurring during FSP which uniformly distributed the SiC particles. The composites containing 16 vol% SiC could not be fully consolidated using FSP, and contained residual pores and lack of consolidation which originated from the as-received sintered microstructure. The hardness correlated well with the mean inter-particle spacing for the SiC particles in the case of composites containing 4 and 8 vol% SiC.     

Laser-assisted friction stir processing of IN738LC nickel-based superalloy: stir zone characteristics

Friction stir processing (FSP) of high softening-temperature materials such as nickel-based superalloys is considered to be difficult. Laser heating of a localised area ahead of the FSP tool was used to provide sufficient plasticity during the FSP of IN738LC nickel-based superalloy. The stir zone (SZ) microstructure of the friction stir processed and laser-assisted friction stir processed were characterised. Laser-assisted friction stir processing (LAFSP) produced a defect-free pass, but FSP resulted in generation of a discontinuity in the SZ. Both lower volume fraction of partially dissolved γ′ precipitates and coarser grain structure of SZ in LAFSP led to more ductility of the SZ material and elimination of the defects.