Papers by Keyword: Friction Stir Processing (FSP)

Abstract: Friction stir processing (FSP) has successfully evolved as a technique in fabricating surface composite. An alternative technique on fabrication of a SiC-reinforced Al6061 aluminum matrix composite (AMC) by stirring copper-coated SiC particles into matrix to form a reinforced zone was developed. Copper film was deposited onto the SiC particles by electroless plating and by photodeposition processes. The copper coating serves as an adhesion and diffusion layer to enhance the cohesion between the particles and the matrix. It is to expect that the strength of the AMC could be improved. The uniformity of particle distribution in the stir zone (SZ) was improved by adjusting the location of particle insert and by a double-pass stir. T5 post weld heat treatment (PWHT) was conducted to retrieve the hardness and the strength of the SZ to the strength level of the matrix. While the submicron-thick Cu-coating was partially separated from SiC particles after FSP, photodeposition Cu-coating less than 100 nm thick exhibited a better adhesion to the SiC particles. The EPMA analysis across the interface shows evidence of interdiffusion between copper and aluminum which implies an enhanced cohesion between the particles and matrix. After PWHT, while the SZ containing photodeposition Cu-coated SiC exhibited the highest hardness among different SZs, the SZ containing electroless Cu-coated SiC exhibited the highest strength. The possible mechanisms for the improvement of the hardness and strength were discussed. In summary, the purpose of fabricating a locally particulate-reinforced Al6061 AMC by stirring Cu-coated SiC particles into Al6061 matrix was achieved. Keywords:Friction stir processing (FSP), particulate reinforced AMC, electroless plating, photodeposition, copper-coated SiC particles

Abstract: Grain size determines to a large degree the mechanical properties of the friction stir processed (FSP) material. Developed in this work is a numerical (FEM) based-model for predicting values of the Zener-Hollomon parameter (Z-parameter) as function of input process parameters during friction stir processing of AZ31B. Prediction of Z values is desirable given that direct relations exist between the Z-parameter and the average grain size in the dynamically recrystallized zone (DRX). For this purpose, utilized in this work is a robust finite element model with a suitable constitutive equation and boundary conditions the results of which have been previously validated against published experimental data. A virtual test matrix constituting of 16 cases (4 spindle speed, N, x 4 feed, f) was run. Based on resulting state variables of strain rates and temperatures at a representative point within the stir zone, a statistically-validated power equation model was developed that relates Z-parameter values to input parameters of speed and feed. The results of the numerically developed power equation were validated against experimental results. This model can be readily used in future control frameworks to FSP produce AZ31B sheets of a predefined target grain size.

Abstract: In this study, the high-temperature ductility of a fine-grained, polycrystalline 5083 solid solution alloy was investigated. The composition of the alloy in mass% was Al–4.5 Mg–0.68 Mn–0.19 Fe–0.13 Si–0.11 Cr. Grain refinement was effectively achieved in the stir zone by a friction stir process, and the grain size could be reduced to 3.7 μm. Tensile tests were performed at temperatures ranging from 643 to 743 K and strain rates ranging from 0.001 to 0.1 /s. The stress–strain curves showed that the flow stress continuously decreased until it reached a maximum value of stress and fractured after the initial strain hardening occurred. The value of elongation-to-failure was more than 100% when temperatures were greater than 693 K. The high ductility observed at this point can be referred to as superplastic-like elongation. This phenomenon has been reported in some Al–Mg alloys. The experimentally determined stress exponent (n value) and activation energy for deformation were about 2.5 and 123 kJ/mol, respectively. These results suggest that the grain boundary sliding, accompanied by solute drag motion of dislocations, was a rate controlling process for deformation.

Abstract: Utilizing a proper material model for describing the mechanical behavior of any material is key for a successful simulation of friction stir processing (FSP) where temperature, strain, and strain rate gradients vary abruptly within, and when moving away, from the stirring zone. This work presents a comparison of how faithfully do three different constitutive equations reproduce the state variables of strain, strain rate, and temperature in an FEM simulation of a test-case FSP (1000 rpm spindle speed, and 90 mm/min feed). The three material models considered in this comparison are namely: Johnson-Cook (JC), Sellars-Tegart (ST), and Zerilli-Armstrong (ZA). Constants for these constitutive equations are obtained by fitting these equations to experimental mechanical behavior data collected under a range of strain rates and temperatures of twin-rolled cast wrought AZ31B sheets.It is widely recognized that JC-based models over predicts stress values in the stir zone whereas ST-based models are incapable of capturing work hardening outside of the stir zone. Therefore, a ZA model, being a physical based-HCP specific model, is hereby investigated for its suitability as a material model that would overcome such drawbacks of JC-and ST-based models. The equations from the constitutive models under consideration are fed into an FEM model built using DEFORM 3D to simulate the traverse phases of a friction stir process. Amongst these three material models, comparison results suggest that the HCP-specific ZA model yield better predictions of the state variables: strain, strain rate, and temperature, and, consequently, the estimated values for flow stresses.

Abstract: Roller burnishing (RB) and friction stir processing (FSP) were applied to a cast aluminum alloy, AC4CH-T6 (equivalent to A356-T6), to improve the fatigue properties. In roller burnished specimens, Vickers hardness was increased until the depth of 60μm compared with that of the as-cast specimens, resulting in work-hardening by RB. The compressive residual stress on the surface of the roller burnished specimens was also increased from 35MPa to 132MPa. In order to investigate the effect of RB on the fatigue properties, rotary bending fatigue tests have been performed using the roller burnished and the as-cast specimens. The roller burnished specimens exhibited higher fatigue strength than the untreated specimens. It is due to the increase in hardness and compressive residual stress by RB. In addition, plane bending fatigue tests have been performed using the friction stir processed and untreated specimens. Fatigue strengths of the friction stir processed specimens were highly improved compared with untreated specimens as the results of the elimination of casting defects by FSP. However, the crack growth rates of the friction stir processed specimens were faster than those of untreated specimens. It is due to the softening of the material by heat input during the FSP.

Abstract: The AlN particles reinforced composite was fabricated on the surface of aluminum 6061-T6 alloy rolled plate by five passes friction stir processing (FSP). Microstructure of FSPed sample was characterized by optical microscope and scanning electron microscope. AlN particles in composite were verified by EDS and XRD. Microhardness and resistance to wear were also investigated. Results show that grains in composite were refined by dynamic recrystallization and uniformly dispersed AlN particles. Composite region bonded with the Al substrate well. No reaction occurred at the interface between AlN and Al matrix. By comparison with base metal, the FSP-produced composite exhibited improved microhardness and substantial wear weight loss reduction.

Abstract: The main aims of this study is to produce copper reinforced metal matrix composite (MMC) using micron sized chromium particles via friction stir processing (FSP) in order to studying effects of adding Cr particles to copper based matrix by FSP.Microstructures, microhardness and wear properties have been studied in order to evaluate the microstructures and mechanical properties of fabricated composites. the microstructure properties are evaluated by optical microscopy (OM) and field emission scanning electron microscopy (FESEM). The mechanical behaviors of the samples are determined by microhardness and wear tests. The results showed that the grain size of fabricated composite reduced. also it is indicated that in comparison to base copper microhardness of FSPed composites in stir zone (SZ) have been increased significantly. the results of wear test showed that in comparison with specimen with traverse speed of 80 mm/min , higher traverse speed of 160 mm/min increase wear rate of cylindrical pins.

Abstract: Recently, friction stir processing (FSP) was developed as an effective method to modify microstructural and mechanical properties of materials. During process, a rotating tool is inserted in a plate, providing frictional heating and mechanical mixing. In this investigation, the effect of annealing heat treatment on the microstructure characteristics of the nugget zone was investigated during friction stirs processing (FSP) of the pure copper. Plate with 4 mm thickness was friction stir processed at constant traverse speed of 45 mm/min and tool rotation speed of 700 rpm. Samples were processed in various annealing conditions. Results showed that by increasing the annealing duration from 45 to 180 minutes at annealing temperatures of 600°C and 800°C, the grain size and the hardness value of samples significantly decreased. At annealing temperature of 1000°C samples were exposed to extra heat, grains started to coarsen and hardness decreased. Ultrafine-grained microstructure in FSP samples was achieved using annealing heat treatment at annealing temperature of 600°C.

Abstract: mproving ductility in metals using friction stir processing (FSP) is a challenging effort and is made by means of a rotating tool inserted in a work piece providing heat transfer and plastic deformation. In this investigation, improving ductility during FSP was determined as a purpose and the microstructure and mechanical properties of nugget zone were investigated during friction stir processing (FSP) of pure copper. Ductility was measured using tensile elongations at a temperature of 20 °C. By varying the traverse speed from 40 to 100 mm/min at rotation speeds of 300 and 600 rpm, the ultrafine grain microstructure was achieved .Defects were observed in rotational speed of 300 rpm. By increasing traverse speed at constant rotational speed of 600 rpm grain size of the nugget zone decreased and ductility increased. Achievable ductility was limited by cavity formation due to lower heat input and deformation in samples with defects.

Abstract: Recently friction stir processing (FSP) was developed as a generic implement for microstructural modification based on the principles of FSW using a rotating tool inserted in a monolithic work piece which provides frictional heating and mechanical mixing. In this paper, the microstructural evolution characteristics of nugget zone were investigated during friction stir processing (FSP) of pure copper. Pure copper plates were friction stir processed to the depth of 3.4 mm at different process conditions by varying the traverse speed from 30 to 120 mm/min at rotation speeds of 400 and 600 rpm..Defects were observed in rotational speed of 400 rpm. Grain size of NZ depended significantly on plastic deformation and heat input value. By increasing traverse speed at constant rotational speed of 600 rpm grain size of the nugget zone decreased and the hardness increased. Ultimate tensile strength increased with decrease in grain size. FSP was found as an effective method to develop fine-grained microstructure in copper plates.