Showing papers on "Friction stir processing published in 2003"

Friction stir processing: a novel technique for fabrication of surface composite

Abstract: A novel surface modifying technique, friction stir processing (FSP), has been developed for fabrication of surface composite. Al–SiC surface composites with different volume fractions of particles were successfully fabricated. The thickness of the surface composite layer ranged from 50 to 200 μm. The SiC particles were uniformly distributed in the aluminum matrix. The surface composites have excellent bonding with the aluminum alloy substrate. The microhardness of the surface composite reinforced with 27vol.%SiC of 0.7 μm average particle size was ∼173 HV, almost double of the 5083Al alloy substrate (85 HV). The solid-state processing and very fine microstructure that results are also desirable for high performance surface composites.

High strain rate superplasticity in a commercial 2024 Al alloy via friction stir processing

Abstract: A novel technique for producing high-strain-rate-superplastic (HSRS) microstructure via friction stir processing (FSP) in a commercial 2024 Al has been demonstrated. A maximum ductility of ∼525% has been achieved at a strain rate of 10 −2 s −1 and 430 °C. Current results suggest that friction stir processing can be developed as a simple yet effective technique for producing microstructure amenable for superplasticity at high strain rates and/or lower temperatures and at lower flow stresses.

High strain rate superplasticity in friction stir processed Al–Mg–Zr alloy

Abstract: Al–4Mg–1Zr extruded bar was subjected to friction stir processing (FSP), resulting in generation of a fine microstructure of 1.5 μm grain size. Superplastic deformation behavior of FSP Al–4Mg–1Zr alloy was investigated in strain rate range of 1×10−3 to 1 s−1 and temperature range of 350–550 °C and compared with that of as-rolled one. It is indicated that the FSP alloy exhibited significantly enhanced superplasticity at a high strain rate of 1×10−1 s−1, and a maximum elongation of 1280% was obtained at 525 °C and 1×10−1 s−1. Further, the FSP Al–4Mg–1Zr alloy exhibited excellent thermal stability at high temperature, and a large elongation of 1210% was observed at 550 °C and 1×10−1 s−1. Moreover, FSP resulted in a significant decrease in the flow stress in Al–4Mg–1Zr alloy. At a strain rate of 1×10−2 s−1, the flow stress (∼7 MPa) of FSP Al–4Mg–1Zr at 450 °C was comparable to that of as-rolled alloy at 550 °C.

A new route to bulk nanocrystalline materials

Abstract: Despite their interesting properties, nanostructured materials have found limited use as a result of the cost of preparation and the difficulty in scaling up. Herein, the authors report a technique, friction stir processing (FSP), to refine grain sizes to a nanoscale. Nanocrystalline 7075 Al with an average grain size of 100 nm was successfully obtained using FSP. It may be possible to further control the microstructure of the processed material by changing the processing parameters and the cooling rate. In principle, by applying multiple overlapping passes, it should be possible to produce any desired size thin sheet to nanostructure using this technique. We expect that the FSP technique may pave the way to large-scale structural applications of nanostructured metals and alloys.

Thick-section metal forming via friction stir processing

Abstract: Friction stir processing (FSP) modifies the surface microstructure of metals so that thick-section metal workpieces can be bent over large angles without formation of surface cracks. A thick 2519-T8 aluminum plate (25.4 mm thick and 50.8 mm wide) was friction stir processed across the pre-tensile surface to a depth of 6.3 mm, and was then bent at room temperature over a punch with radius 38.1 mm into a v-shaped die to an 80° bend angle. Whereas unprocessed workpieces of this type exhibited surface cracking at 31° bend angle and failed at 40° bend angle, no cracking was evident for the friction stir processed workpiece up to 80° bend angle.

Stir forming apparatus and method

Abstract: An apparatus and method for forming a workpiece to a desired, non-planar configuration are provided. At least one friction stir forming tool, having a shoulder and a pin, is used to urge the workpiece to the desired configuration and friction stir form the workpiece. The forming tool can urge the workpiece against a contour surface of a die or a shoulder that is opposite the structural member from the tool. Thus, the forming tool plasticizes a portion of the workpiece and urges the workpiece to the desired configuration. In addition, the material properties of the workpiece can be improved by the friction stir processing.

Characterization of Microstructure and Microtexture in Longitudinal Sections from Friction Stir Processed Nickel-Aluminum Bronze

Abstract: : Cast nickel-aluminum bronze (NAB) is the material of choice for propellers in both surface ships and submarines. New designs require a material with improved strength and hardness while retaining NAB's corrosion resistance. Friction stir processing (FSP) represents a new technology for surface hardening of as-cast NAB by means of severe plastic deformation induced by a rotating tool that is traversed across the surface of a material. FSP can convert a microstructure from a cast to a wrought condition without altering the overall shape of the object being worked. The purpose of this study is to apply recently developed orientation imaging microscopy (OIM) methods to evaluate the influence of FSP on microstructure and microtexture of an as-cast NAB material. Processed material was examined in planes having both longitudinal and transverse orientations with respect to tool motion. Shear textures in the thermomechanically-affected zone (TMAZ) were of particular concern. Results of the analysis of this work will be described and the implications to FSP of NAB propeller materials will be delineated.

The Effects of Isothermal Deformation and Annealing on the Microstructure of Nickel-Aluminum-Bronze Propeller Material

Abstract: : This thesis is a study of annealing and deformation characteristics of cast Nickel-Aluminum Bronze (NAB) in relation to Friction Stir Processing (FSP) of this material. Cast NAB is widely utilized by the U.S. Navy as material used in the production of propellers for surface vessel and submarines. FSP is a novel method of deformation processing that is conducted by use of a rotating tool that is forced onto the surface of a material under load such that sliding and sticking friction result in a combination of frictional and adiabatic heating due to plastic deformation. A stirring effect results in the formation of a zone of severe shear deformation and local temperatures approaching 90% of the melting temperature. FSP results in local homogenization of the cast microstructure and conversion of it to a wrought condition, but also in steep strain, strain rate and temperature gradients. In this thesis microstructures achieved through controlled isothermal deformation and annealing processes will be compared with microstructures resulting from FSP. The use of Friction Stir Processing is envisioned as a way to improve the surface characteristics of the material through localized microstructural modification. Studies of warm rolling, channel die compression and various annealing schedules were completed.

Microtextural characterization of shear textures in the thermo-mechanically affected zone of friction stir processed nickel aluminum bronze

Abstract: : Cast nickel-aluminum bronze (NAB) is used in the production of the Navy's marine propellers for both surface and submersible platforms. Improving the properties of NAB will facilitate new designs. Friction Stir Processing (FSP) is a solid state, thermo-mechanical process to achieved surface hardening of cast NAB by use of a rotating tool that is plunged into and traversed across the material surface. The subsequent "stirring" action produces local yielding/softening of the material by frictional as well as adiabatic heating. The softened regions experience extensive shear deformations resulting in refinement and homogenization of the local microstructure. In essence, FSP can be used to achieve a wrought microstructure from as-cast nickel-aluminum bronze in the absence of macroscopic shape change. There is a region known as the Thermo-mechanically Affected Zone, or TMAZ, in material that has experienced FSP. This region, similar to the heat affected zone (HAZ) common in fusion welding, displays a microstructure characteristic of one affected by diffusion of heat, as well as deformation induced by the rotating tool resulting in the development of shear textures. Using Orientation Imaging Microscopy (OIM) these shear textures were analyzed and characterized for two separate FSP conditions. Through OIM, shear textures in the TMAZ were characterized to be of the C-type, with varied lattice orientations. Shear directions were predominately in the direction of tool advance for one processing condition, while tangent to the tool interface for the other.