Vahid Rezazadeh

Bio: Vahid Rezazadeh is an academic researcher from University of Tabriz. The author has contributed to research in topics: Friction stir processing & Physics. The author has an hindex of 4, co-authored 7 publications receiving 60 citations.

Modified Friction Stir Channeling: A Novel Technique for Fabrication of Friction Stir Channel

Abstract: Friction stir channeling (FSC) is a simple method for fabrication of a continuous, integral channel in a monolithic plate, which is carried out in a single pass. The fabricated channels can be applied in heat exchanger industry. In this study, a novel technique was introduced to produce channels in 6061 aluminum alloy which is named as Modified Friction Stir Channeling (MFSC). This technique is derived from Friction stir processing. In this technique, the tool profile and position of tool pin against work piece were designed differently from FSC process. Channels were fabricated with a very regular shape such as rectangular. Comparison between MFSC and FSC showed that fabricated channels, using MFSC process, had better properties relative to fabricated channels by FSC.

Channel Formation in Modified Friction Stir Channeling

Abstract: Modified friction stir channeling (MFSC) is a new approach for fabrication of a continuous, integral channel in monolithic Al plate, which is carried out in a single pass. This technique is derived from Friction Stir Processing (FSP). Tool profile and position of tool pin against work piece were designed differently from conventional Friction Stir Channeling (FSC) process. In MFSC, Fabricated channel with more regular shape than FSC process shows that the channel formation mechanism is different from FSC. So, in this study, in order to understand the formation of channel, material flow in MFSC is investigated using weakened tool pin technique. Moreover, one of the most important channel properties is width of channel. This characteristic affected the channel area and shape of the channel. Width of channel was unknown in FSC process. But in MFSC, a new region is investigated which determines the channel width.

Fracture Mechanism in Friction Stir Processed Annealed Pure Copper Samples

Abstract: Fracture mechanism in metals using Friction Stir Processing (FSP) is a challenging investigation and is made by means of a rotating tool inserted in a work piece providing heat transfer and plastic deformation. In this paper, improving ductility during FSP was determined as a purpose and the microstructure and fracture mechanism of samples were investigated during Friction Stir Processing (FSP) of pure copper. Ductility was measured using tensile elongations at 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. Despite the cavity formation during process, friction stir processing technique was successfully applied to acquire samples with high ductility and certain minimum grain sizes for copper plates.

Microstructural Refinement of Pure Copper by Friction Stir Processing

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.

An effective anisotropic visco-plastic model dedicated to high contrast ductile laminated microstructures: Application to lath martensite substructure

Abstract: In particular types of layer- or lamellar-like microstructures such as pearlite and lath martensite, plastic slip occurs favorably in directions parallel to inter-lamellar boundaries. This may be due to the interplay between morphology and crystallographic orientation or, more generally, due to constraints imposed on the plastic slip due to the lamellar microstructural geometry. This paper proposes a micromechanics based, computationally efficient, scale independent model for particular type of lamellar microstructures containing softer lamellae, which are sufficiently thin to be considered as discrete slip planes embedded in a matrix representing the harder lamellae. Accordingly, the model is constructed as an isotropic visco-plastic model which is enriched with an additional orientation-dependent planar plastic deformation mechanism. This additional mode is activated when the applied load, projected on the direction of the soft films, induces a significant amount of shear stress. Otherwise, the plastic deformation is governed solely by the isotropic part of the model. The response of the proposed model is assessed via a comparison to direct numerical simulations (DNS) of an infinite periodic two-phase laminate. It is shown that the yielding behavior of the model follows the same behavior as the reference model. It is observed that the proposed model is highly anisotropic, and the degree of anisotropy depends on the contrast between the slip resistance (or yield stress) of the planar mode versus that of the isotropic part. The formulation is then applied to model the substructure of lath martensite with inter-layer thin austenite films. It is exploited in a mesoscale simulation of a dual-phase (DP) steel microstructure.The results are compared with those of a standard isotropic model and a full crystal plasticity model.

High temperature characteristics of Al2024/SiC metal matrix composite fabricated by friction stir processing

Abstract: In the present study, friction stir processing (FSP) is used for the synthesis of an aluminum metal matrix composite (MMC) reinforced by SiC particles. MMC specimens with reinforced microstructures exhibited significant improvement in hardness (near 50%). Isothermal uniaxial tensile tests were employed for the as-received, friction stir processed and composite microstructures at ambient and high temperatures under strain rates ranging from 10−2 to 10−4 s−1 to investigate the effect of deformation rate on the mechanical behavior. At ambient temperature, notable improvement of the yield strength was observed reaching about 240% of the as-received samples while the ductility was reduced near to 4%. Elevated temperature flow curves were perceptibly sensitive to strain rate, especially for FSPed and MMC samples. Fracture surface observations hinted at the distribution of second phase particles along with possible damage mechanisms.

Influence of machine parameters on material flow behavior during channeling in modified friction stir channeling

Abstract: Material flows during friction stir processes are very complex and not fully understood. Although the most literature reviews are presenting for material flow path, but Modified Friction Stir Channeling (MFSC) is a novel process based on Friction Stir Processing (FSP), which is being utilized to produce internal channel in Monolithic plates. A new flow pattern, in this study, is proposed to investigate material flow path and channel formation mechanism. The validity of this model is demonstrated by observing the cross-section and created keyhole using stop-action technique. The main difference between Friction Stir Channeling (FSC) and MFSC is the tilt angle. The effect of tilt angle and process parameters such as rotational speed and traverse speed on material flow path is studied. The results indicate that the tilt angle is an effective factor on forging of material behind of pin in the Advancing Side (AS) and also in the upper portion of channel roof imperfections. The rotational speed is an effective parameter on extruded material around the tool pin body and the extracted material in front of tool pin, because of the changing in the slip–stick condition and generated heat by tool. Traverse speed was an effective parameter on forging action of material and to keep material nearby tool pin in the behind of pin.