Showing papers on "Friction stir processing published in 2016"

Fabricating Superior NiAl Bronze Components through Wire Arc Additive Manufacturing.

Abstract: Cast nickel aluminum bronze (NAB) alloy is widely used for large engineering components in marine applications due to its excellent mechanical properties and corrosion resistance. Casting porosity, as well as coarse microstructure, however, are accompanied by a decrease in mechanical properties of cast NAB components. Although heat treatment, friction stir processing, and fusion welding were implemented to eliminate porosity, improve mechanical properties, and refine the microstructure of as-cast metal, their applications are limited to either surface modification or component repair. Instead of traditional casting techniques, this study focuses on developing NAB components using recently expanded wire arc additive manufacturing (WAAM). Consumable welding wire is melted and deposited layer-by-layer on substrates producing near-net shaped NAB components. Additively-manufactured NAB components without post-processing are fully dense, and exhibit fine microstructure, as well as comparable mechanical properties, to as-cast NAB alloy. The effects of heat input from the welding process and post-weld-heat-treatment (PWHT) are shown to give uniform NAB alloys with superior mechanical properties revealing potential marine applications of the WAAM technique in NAB production.

Influence of Friction Stir Processed Parameters on Superplasticity of Al-Zn-Mg-Cu Alloy

Abstract: Friction stir processing (FSP) is a novel technique for refining the microstructure. In this study, the effect of FSP process parameters such as tool rotation, traverse speed and tool tilt on resulting grain size, microstructure and superplastic behavior of high-strength thick Al-Zn-Mg-Cu alloy is reported. The microstructure examination of the stir zone (SZ) was performed by optical as well as scanning electron microscope. Microstructure variation attributed to different process parameters is reflected in the SZ. It is observed that grain size increases with increasing tool rotation speed, and decreases with increasing traverse speed. However, tool tilt has no significant effect on grain size. Moreover, at higher tool tilt distorted grains were observed in microscopic images. The highest average value of hardness in the SZ is obtained for low heat input value corresponding to higher tool rotation and traverse speed. In this study, hardness has shown no dependency on the grain size of the SZ due to the st...

Influence of multi-pass friction stir processing on the microstructure and mechanical properties of Al-5083 alloy

Abstract: Samples with one through three passes with 100% overlap were created using friction stir processing (FSP) in order to locally modify the microstructure and mechanical properties of a cold-rolled Al-5083 alloy. A constant traverse speed and two different rotational speeds were used for processing. The results indicated that single-pass FSP caused dynamic recrystallization in the stir zone, leading to equiaxed grains with high angle grain boundaries. The grain size increased with increasing the rotational speed. The product of ultimate tensile strength and total elongation of the stir zone was significantly enhanced compared with that of the base metal. During the annealing heat treatment, abnormal grain growth (AGG) occurred throughout the stir zone when a low rotational speed was adopted. The stir zone produced with a high rotational speed was found to be more resistant to AGG. The application of multiple process passes did not change the grain size and mechanical properties of the stir zone significantly. The expanding of AGG in the stir zone was inhibited as the number of passes was increased.

Fabrication of a new Al-Al2O3-CNTs composite using friction stir processing (FSP)

Abstract: A new Al-Al 2 O 3 -CNTs Composite has been successfully fabricated using friction stir processing. Uniform dispersion of nano-particles in the metal matrix was observed. Significant improvement in the micro-hardness and tensile strengths were obtained through the addition of nano particles. In particular the yield strength of the composites increased 70% compared with that of friction stir processed Al when both Al 2 O 3 and CNTs were added in the matrix. The improvement in the mechanical properties is mainly attributed to grain refinement and Zener pinning effect caused by the addition of nano-sized particles. Al 2 O 3 particles were observed at the bottom of the dimples at the fracture site, suggesting voids initiation at the Al/Al 2 O 3 interfaces regions. The reinforcing mechanism with multiple nano-particles addition was discussed therein.

Superplasticity of a nano-grained Mg–Gd–Y–Zr alloy processed by high-pressure torsion

Abstract: While most of the reports on Mg–Gd–Y–Zr alloys report superplasticity after extrusion or friction stir processing, it is important to investigate superplasticity in these alloys after other severe plastic deformation processes having greater grain refinement capability. Accordingly, superplasticity was studied in an Mg–9Gd–4Y–0.4Zr (GW94) alloy after different high-pressure torsion (HPT) conditions. The HPT was performed at room temperature under an applied pressure of 6.0 GPa for up to 16 turns. TEM microstructural characterization revealed that the grain size was reduced from an initial value of ~8.6 μm in the extruded condition to ~95±10 and ~85±10 nm after 8 and 16 turns, respectively. A shear punch testing method was used for evaluation of superplasticity at 573, 623, 673 and 723 K. Maximum strain rate sensitivities of ~0.51±0.05 and ~0.48±0.05 were obtained at 623 K for the material processed through 16 and 8 turns, respectively. This strain rate sensitivity and an activation energy of ~100±5 kJ mol –1 suggests the occurrence of grain boundary sliding in the superplastic region.

Evaluation of the microstructure and wear behaviour of AA6063-B4C/TiB2 mono and hybrid composite layers produced by friction stir processing

Abstract: Friction stir processing (FSP) was used to produce mono and hybrid surface composite layers of aluminium matrix containing B 4 C and TiB 2 particles. For this purpose the AA6063 was used as the base material. Different fractions of milled B 4 C and in situ TiB 2 –10 wt.%Al composite powder produced by mechanical alloying were incorporated into the matrix by FSP. The effect of different ratios of TiB 2 and B 4 C reinforcing particles on the microstructure and wear resistance of surface layers was studied. Microstructural evaluation of the samples was conducted by optical microscopy and field emission scanning electron microscopy (FESEM) of the cross-sections of surface composite layers. Microhardness testing was conducted across the cross-sections of FSPed samples to obtain hardness profiles and pin on disk dry sliding wear test was conducted on FSPed samples. The results showed that the incorporation of B 4 C and TiB 2 reinforcing particles to the surface increased the hardness and wear resistance of composite layers in comparison with FSPed AA6063 alloy. Moreover, 100%TiB 2 surface composite layer exhibited the highest hardness and best wear behaviour compared to other fractions.

Friction-stir processing of an AA8026-TiB2-Al2O3 hybrid nanocomposite: Microstructural developments and mechanical properties

Abstract: In this study, micro- and nano-sized TiB 2 and Al 2 O 3 particles were incorporated separately and simultaneously through the AA8026 aluminum base alloy during multi-pass friction stir processing (FSP) with 100% overlapping to fabricate metal matrix mono and hybrid nanocomposites. Various FSP conditions including different rotational speeds ( w ), traverse velocities ( v ), and processing pass numbers were assessed to attain a homogenous distribution of reinforcing particles through the Al-metal matrix. Moreover, the impacts of size (micro or nano) and type of reinforcement particles (TiB 2 and Al 2 O 3 ) on the process-ability of single and hybrid nanocomposite systems were examined. Microstructures of different zones and distributions of reinforcing ceramic particles through the Al-matrix under various processing conditions were studied and characterized by using optical (OM), scanning (SEM), and transmission electron microscopy (TEM) techniques, respectively. The main mechanical characteristics of the prepared nanocomposites, such as, indentation Vickers hardness, tensile properties, and wear resistance were measured and compared for all of the various processing conditions. By optimization of the FSP parameters, as a rotational speed of 1600 rpm and a traverse velocity of 40 mm/min after 4 passes, a uniform AA8026-TiB 2 -Al 2 O 3 hybrid nanocomposite was attained with significant improvements (~70–100%) in the different mechanical properties. As a result, the tensile yield strength of ~270 MPa, elongation of ~4.5%, and indentation Vickers hardness of ~141 HV were obtained. Also, the average wear rate was reduced from the 21×10 −3 mg/m value for the AA8026 base alloy down to 2.6×10 −3 mg/m for the best processed nanocomposite. A direct relationship between the wear rate and the indentation hardness resistance was demonstrated. Finally, effects of FSP processing conditions and reinforcement particles (type and size) on the microstructure and mechanical properties of the FSPed Al-matrix nanocomposites were addressed and discussed.

Modification of a cold sprayed SiCp/Al5056 composite coating by friction stir processing

Abstract: The SiC particles reinforced Al5056 composite coating was deposited onto a pure Al substrate by cold spraying (CS) of a powder mixture having 45 vol.% SiC, and then modified by friction stir processing (FSP) with a threaded stir tool probe aiming to study the changes in microstructure and tribological behavior of the composite coating before and after the FSP treatment. Results showed that the coatings consisted of two phases of Al and SiC, and no other diffraction peaks were detected in FSPed coating. The sizes of reinforcement particles in the FSPed composite coating were substantially refined from 12.2 μm to 4.4 μm due to the severe stir effect of the tool at a rotating speed of 1400 rpm. The refined SiC particles exhibited a homogenous distribution in the FSPed coating. A dramatic increase in microhardness from 92.5 HV to 185.7 HV was observed due to the redistribution and refinement of reinforcements in the FSPed coating. The average coefficients of friction (COF) of the as-sprayed and FSPed coatings were 0.25 and 0.39, respectively. The higher COF of the FSPed coating was the effect of increased microhardness and friction force which originated from the uniformly dispersed SiC particles embedding the matrix.

Friction Stir Processing as a Novel Technique to Achieve Superplasticity in Aluminum Alloys: Process Variables, Variants, and Applications

Abstract: This article provides an overview of the potential for superplasticity of aluminum alloys using friction stir processing (FSP). FSP is a variant of friction stir welding (FSW), and FSP is an effective technique to alter the metallurgical and mechanical properties of the material, which results in superplastic properties at high strain rate and low temperature. This makes FSP as an attractive and cost-effective method to produce superplastic materials. A detailed summary of previously reported superplasticity in all aluminum alloys using FSP is tabulated in this review. It reveals the influence of tool design, machine variables, number of passes, active cooling, grain size, superplastic temperature, strain rate, and elongation on the superplastic properties of FSP aluminum alloys. Variants of FSP to achieve superplasticity at optimized conditions are proposed based on dual rotation of tool and additional cooing during the process. Applications of superplastic forming in aerospace and automotive are discussed. The direction of research in friction stir-processed superplasticity is covered in future scope.

Effect of ceramic particulate type on microstructure and properties of copper matrix composites synthesized by friction stir processing

Abstract: Friction stir processing (FSP) has been established as a novel solid state technique to produce bulk and surface metal matrix composites. The present work aim to produce copper matrix composites (CMCs) using FSP and analyze the effect of ceramic reinforcement type (SiC, Al 2 O 3 , B 4 C and TiC) on the evolving microstructure, microhardness and wear resistance behavior. A groove was made on 6 mm thick copper plates and packed with various ceramic particles. A single pass FSP was carried out using a tool rotational speed of 1000 rpm, travel speed of 40 mm/min and an axial force of 10 kN. The microstructure and distribution of the ceramic particles were studied using optical and field emission scanning electron microscopy. The sliding wear behavior was evaluated using a pin-on-disk apparatus. The results indicate that the variation in the stir zone, distribution, grain size, hardness and wear resistance of CMCs were within a short range. Nevertheless, Cu/B 4 C CMC exhibited superior hardness and wear resistance compared to other CMCs produced in this work under the same set of experimental conditions.

Friction Stir Processing Strategies for Uniform Distribution of Reinforcement in a Surface Composite

Abstract: Friction stir processing (FSP) is an important technique for preparing surface composites. Fabricating defect-free surface composites with uniform particle distribution by FSP is a challenging task. In this study, silicon carbide particles reinforced AA5083 alloy surface composites was fabricated using different FSP strategies including variation in process parameters, dual-tool processing and tool offset overlapping. Material flow of the processed material with reinforcement particles demonstrated that the distribution of particles was influenced by the stirring action of the probe as well as the extrusion of the plasticized material due to the movement of the tool. Process parameters, particularly rotational speed, showed a dominant influence on the distribution of silicon carbide particles.

Fabrication of tungsten particles reinforced aluminum matrix composites using multi-pass friction stir processing: Evaluation of microstructural, mechanical and electrical behavior

Abstract: In this paper, tungsten particles were dispersed into 1060 Al matrix by multi-pass friction stir processing (FSP) to fabricate W/1060Al composites. The effects of the number of FSP passes on the microstructure, mechanical properties and electrical resistivity were investigated. Microstructural observations revealed that increasing the number of FSP passes contributed to W uniform distribution and grain refinement without changing the size and morphology of W particles. Detailed interfacial microstructure analysis indicated that an excellent metallurgical bonding consisting of an element solid solution was formed at the W/Al interface. The mechanical test results showed that, as the number of FSP passes increased, the microhardness values were remarkably enhanced with a more uniform distribution and at the same time both the strength and ductility of FSPed composites were also improved. The maximum microhardness, strength and ductility were achieved in 5-pass FSPed composite reaching to approximate 86 HV, 126 MPa and 24%, respectively. It was also found that the W particles reinforced Al composites exhibited excellent electrical conductivity and increasing the number of FSP passes caused a negligible enhancement in the electrical resistivity of FSPed composites.

The influence of multipass friction stir processing on the corrosion behavior and mechanical properties of zircon-reinforced Al metal matrix composites

Abstract: Zircon-reinforced Al metal matrix composites were fabricated by friction stir processing (FSP). Composite materials were analyzed to characterize their microstructure, mechanical properties and corrosion resistance. The number of FSP passes was found to have a significant effect on the microstructure and strength of the composite specimens. Multipass friction stir processing of the composite specimens promoted grain refinement in the base metal and resulted in a uniform dispersion of the reinforcement particles. In addition, increasing the FSP pass number from one to three increased the composite density. Also, corrosion resistance of the composites was severely influenced by the number of FSP passes and presence of reinforcement particles. While, corrosion performance of the composite materials was significantly enhanced as the number of FSP passes increased to two and three passes, a more number of FSP passes reduced the corrosion resistance of composite materials. It was found that process parameters could be easily optimized to enhance the mechanical properties and corrosion resistance of the zircon-reinforced Al metal matrix composites during FSP.

Wear properties of Al–Al2O3/TiB2 surface hybrid composite layer prepared by friction stir process

Abstract: In this study, surface hybrid composite was fabricated on Al6061 base sheets using friction stir processing (FSP). Samples were subjected to various numbers of FSP passes from one to four with Al2O3/TiB2 powder. Influence of number of FSP passes was studied on distribution of Al2O3/TiB2 particles in aluminium matrix, microstructure, hardness, and wear properties of specimens. The results showed that increase in the number of passes causes a more uniform dispersion of composite particles and thus, decreases particles clustering. In addition, an increase in the number of FSP passes was found to decrease the matrix grain size of the surface hybrid composite. It was observed that the hardness increased as the number of passes increased due to presence and pinning effect of hard Al2O3/TiB2 particles. Also, at higher number of passes, the surface hybrid composite wear resistance was increased.