Tribological Behavior of A356/Al2O3 Surface Nanocomposite Prepared by Friction Stir Processing

Surface A356 aluminum alloy matrix composites containing micro and nanosized Al₂O₃ are prepared by a new approach utilizing high-velocity oxy-fuel spraying and friction stir processing (FSP). Optical and scanning electron microscopy, microhardness, and wear tests were used to characterize the surface composites. Results indicated that, the presence of Al₂O₃ in matrix can improve the mechanical properties of specimens. The microhardness of surface composites containing micro and nanosized Al₂O₃ were 89.8 ± 2.6 HV and 109.7 ± 2.5 HV, respectively, which were higher than those for the as-received (79.6 ± 1.1 HV) and the FSPed A356-T6 with no alumina powder (66.8 ± 0.9 HV). Surface composites revealed low friction coefficients and wear rates, which were significantly lower than those obtained for substrate. The wear mass losses of the as-received, the FSPed, and surface micro and nanocomposite specimens after 500-m sliding distance were 50.5, 55.6, 31, and 17.2 mg, respectively. Scanning electron microscopy tests revealed different wear mechanisms on the surface of the wear test specimens.     

Experimental Investigation of Magnesium-Base Nanocomposite Produced by Friction Stir Processing: Effects of Particle Types and Number of Friction Stir Processing Passes

In this research, nanosized SiC and Al₂O₃ particles were added to as-cast AZ91 magnesium alloy, and surface nanocomposite layers with ultrafine-grained structure were produced via friction stir processing (FSP). Effects of reinforcing particle types and FSP pass number on the powder distribution pattern, microstructure, microhardness, and on tensile and wear properties of the developed surfaces were investigated. Results show that the created nanocomposite layer by SiC particles exhibits a microstructure with smaller grains and higher hardness, strength, and elongation compared to the layer by Al₂O₃ particles. SiC particles do not stick together and are distributed separately in the AZ91 matrix; however, distribution of SiC particles is not uniform in all parts of the stirred zone (SZ), which causes heterogeneity in microstructure, hardness, and wear mechanism of the layer. Al₂O₃ particles are agglomerated in the different points of matrix and create alumina clusters. However, distribution of Al₂O₃ clusters in all parts of the SZ is uniform and results in a uniform microstructure. In the specimen produced by one-pass FSP and SiC particles, the wear mechanism changes in different zones of SZ due to the nonuniform distribution of particles. However, in the specimen produced by Al₂O₃ particles, the wear mechanism in all parts of the SZ is the same and, in addition to the abrasive wear, delamination also occurs. Increasing FSP pass number results in improved distribution of particles, finer grains, and higher hardness, strength, elongation, and wear resistance.     

Strain Rate Sensitivity,Work Hardening,and Fracture Behavior of an Al-Mg TiO2 Nanocomposite Prepared by Friction Stir Processing

Annealed and wrought AA5052 aluminum alloy was subjected to friction stir processing (FSP) without and with 3 vol pct TiO₂ nanoparticles. Microstructural studies by electron backscattered diffraction and transmission electron microscopy showed the formation of an ultra-fine-grained structure with fine distribution of TiO₂ nanoparticles in the metal matrix. Nanometric Al₃Ti and MgO particles were also observed, revealing in-situ solid-state reactions between Al and Mg with TiO₂. Tensile testing at different strain rates determined that FSP decreased the strain rate sensitivity and work hardening of annealed Al-Mg alloy without and with TiO₂ nanoparticles, while opposite results were obtained for the wrought alloy. Fractographic studies exhibited that the presence of hard reinforcement particles changed the fracture mode from ductile rupture to ductile-brittle fracture. Notably, the failure mechanism was also altered from shear to tensile rupture as the strain rate increased. Consequently, the fracture surface contained hemispherical equiaxed dimples instead of parabolic ones.     

Fabrications of Surface Nanocomposite by Friction Stir Processing to Improve Mechanical and Microstructural Properties of Low Carbon Steel

Friction stir processing was used to fabricate metal matrix composites on the surface of low carbon steel. In this research for making 2 mm surface MMC, the groove method was applied to fabricate TiB₂ nanocomposite via cylindrical tool made of tungsten carbide. Microstructural properties of FSPed samples were studied by optical microscopy and scanning electron microscopy. To evaluate mechanical properties, the micro hardness and tensile properties of MMC were measured. The results indicated that the surface nanocomposite produced by this method had excellent properties. The microstructure of surface MMCs became fine (ferrite grain size became about 1–2 µm) with no defect and porosity. Moreover by adding TiB₂ nanoparticles to the low carbon steel matrix alloy, mechanical properties were improved. Micro hardness can become 200HV higher than that of the base metal. The surface nanocomposite also exhibited better tensile strength when sample yield stress increased to about 28 %.     

Development of Al-Al3Ni Nanocomposite by Duplex Processing of Flame Spray and Friction Stir Processing,and Evaluation of Its Properties

Metallurgical and Materials Transactions A - In this study, Al-Al3Ni nanocomposite was fabricated by friction stir processing (FSP) of a nickel-deposited Al6061-T6 plate. X-ray diffraction results...     

Sub-zero Temperature Dependence of Tensile Response of Friction Stir Welded Al-Cu-Li (AA2198) Alloy

Mechanical properties at ambient and cryogenic temperatures of Al-Cu-Li alloy are required for design and fabrication of liquid hydrogen and liquid oxygen tanks of satellite launch vehicles. In the present work, bead-on-sheet, friction stir welding was carried out with three different rotation speeds. The yield and strain hardening behaviors of the welds were evaluated in temperature range of 20 K to 298 K. Both yield stress and strain hardening ability in the specimen increased with decrease in testing temperature. The dependence of yield stress on temperature was modeled on the basis of thermally activated dislocation mobility, while that of strain hardening was modeled on the temperature dependence of dynamic recovery rate parameter. The recovery parameter followed an Arrhenius-type relationship with temperature. The model parameters determined from the experimental data were further used to simulate the stress–strain curves at different sub-zero temperatures for the friction stir welds.

     

Fabrication of Wear-Resistant Ti3AlC2/Al3Ti Hybrid Aluminum Composites by Friction Stir Processing

Metallurgical and Materials Transactions A - Hybrid nanocomposites have potential as wear-resistant materials. However, synthesizing these nanocomposites by conventional molten state methods result...     

Microstructural Characteristics and Mechanical Properties of Friction Stir Welded Thick 5083 Aluminum Alloy

Metallurgical and Materials Transactions A - Joining thick sections of aluminum alloys by friction stir welding (FSW) in a single pass needs to overcome many challenges before it comes to...     

Control of Reaction Kinetics During Friction Stir Processing

Friction stir processing (FSP) was used to successfully embed galfenol particles into aluminum (AA 1100 Al) matrix uniformly. However, intermetallic layer of Al₃Fe was formed around the galfenol particles. Activation energy for Al₃Fe formation during FSP was estimated, and attempts were made to minimize the Al₃Fe layer thickness. By changing the processing conditions, FSP successfully eliminated the intermetallic layer. Hence, FSP, in addition to microstructural control, can successfully fabricate intermetallic-free embedded regions by controlling the reaction kinetics.     

A New Strategy for Preparation of NiAl Bronze/Zn Composite by Friction Stir Processing

In this work, we successfully prepared a NAB/Zn composite using Zn wires by friction stir processing (FSP). During FSP, Zn-containing α matrix and (Fe, Ni)Al phases and nano α and CuZn grains with the size of less than 10 nm are formed on the top surface. The average microhardness of the composite is increased by 15 pct compared with the alloy without Zn, which originates from fine grains, CuZn particles strengthening, and more β′ phase.

     

Effect of SiC Particles on Structure Property and Wear Resistance of AA6061/SiC Surface Composite Fabricated Via Friction Stir Processing

Powder Metallurgy and Metal Ceramics - In the present study, the effect of the tool travel and rotational speed on structural properties and wear resistance of 6061Al/SiC surface composites...     

ZrO2-MoSi2/Ni-Si-Mo FGM浸涂成形工艺

对采用粉浆浸涂工艺制备ZrO2-MoSi2／Ni-Si-Mo FGM进行了研究。研究结果表明，采用粉浆浸涂成形ZrO2-MoSi2／Ni-Si-Mo FGM时，每层预涂层的临界厚度为250μm，临界提出速度为0．05mm／s。脱脂、烧结工艺为：5℃／min升温到280℃保温10min，1℃／min升温到500℃保温4h，10℃／min升温到1300℃，5MPa热压1h；脱脂和烧结气氛为氩气气氛。     

Investigation of Bonding Behavior of AA1050/AA5083 Bimetallic Laminates by Roll Bonding Technique

In this study, 1-mm AA1050/AA5083 bimetallic laminates were produced using roll bonding (RB) process. The RB process was carried out with thickness reduction ratios of 25, 50 and 75%, separately. Finite element simulation was used to model the deformation of bimetallic laminates for various experimental conditions. Particular attention was focused on the bonding of the interface between AA1050 and AA5083 layers in the simulation. The optimization of thickness reduction ratios was obtained for improvement of the bond strength of bimetallic laminates during RB process. During the simulation, the mean equivalent strain at the interface zone between the layers was found to reach the maximum value with a high quality bond for the sample produced with 75% of thickness reduction. Moreover, the fracture surface of samples around the interface of laminates after the tensile test was studied to investigate the bonding quality by scanning electron microscopy.     

Friction Stir Processing of Aerospace Aluminum Alloy by Addition of Carbon Nano Tube

Aluminum 7075 is an aerospace alloy that has high strength to weight ratio and used most commonly in aeronautic structures. However, low surface properties such as poor wear resistance and surface hardness are the main weaknesses that limit its application in other areas of manufacturing. In the present work an attempt was made to fabricate aluminum based surface nano-composite reinforced with carbon nano tube (CNT) by means of single pass friction stir processing. Firstly, Microstructural evolution, tensile properties, hardness, wear rate and friction coefficient of fabricated surface composite was compared with pure friction stir processed metal and base material. Hereafter, parametric study based on response surface methodology was carried out to find the effect of tool rotary speed, feed rate and amount of MWCNT on tensile strength and wear rate. Optimization based on desirability approach function was also performed to find optimal parameter setting achieving maximum strength and minimum wear rate, simultaneously. The results revealed that the CNT particles significantly homogenized the microstructure of the composite, enhanced tensile properties and hardness and reduced the wear rate and friction coefficient in sliding test. By performing optimization through RSM, it was found that selection of 1250 RPM tool rotary speed, 40 mm/min feed rate and 0.6 g CNT weight caused 20% improvement in tensile strength and wear rate of fabricated composite when compared with base material.     

Recrystallization Phenomena During Friction Stir Processing of Hypereutectic Aluminum-Silicon Alloy

Microstructural evolution and related dynamic recrystallization phenomena were investigated in overlapping multipass friction stir processing (FSP) of hypereutectic Al-30 pct Si alloy. FSP resulted in the elimination of porosities along with the refinement of primary silicon particles and alpha aluminum grains. These alpha aluminum grains predominantly exhibit high angle boundaries with various degrees of recovered substructure and dislocation densities. The substructure and grain formation during FSP take place primarily by annihilation and reorganization of dislocations in the grain interior and at low angle grain boundary. During multipass overlap FSP, small second phase particles were observed to form, which are accountable for pinning the grain boundaries and thus restricting their growth. During the multipass overlap FSP, the microstructure undergoes continuous dynamic recrystallization by formation of the subgrain boundary and subgrain growth to the grain structure comprising of mostly high angle grain boundaries.     

Heat-Affected Zone Liquation Cracking Resistance of Friction Stir Processed Aluminum-Copper Alloy AA 2219

Metallurgical and Materials Transactions B - In the current work, the effect of friction stir processing on heat-affected zone (HAZ) liquation cracking resistance of aluminum-copper alloy AA 2219...     

Investigations on the Effect of Cyclic Heat Treatment on the Mechanical Properties of Friction Stir Welded Aluminum Alloys (AA5052 & AA6061)

Russian Journal of Non-Ferrous Metals - Friction stir welding is one of the promising techniques to join dissimilar aluminum alloys. In this study, the friction stir welding technique is...