User:Watermelon24/sandbox/Friction stir processing

Friction stir processing is a process that allows changes to specific properties of metals. This occurs by using a rapidly rotating tool that traverses along the metal. The metal uses fine grain of a second metal, with the desired properties for the base metal to have, to be blended in to help improve the specific properties of the base metal. The rapid rotating tool is then navigated over the specific area desired to be improved and join the two metals into one. Friction stir processing is used commonly by mechanical engineers in the aerospace and automobile industry looking for new ways to improve durability in a material all the while maintaining a low cost.

Process

In friction stir processing (FSP), a rotating tool is used with a pin and a shoulder to a single piece of material to make specific property enhancement, such as improving the material’s toughness or flexibility, in a specific area in the micro-structure of the material via fine grain of a second material with properties that improve the first.(MA) Friction between the tool and workpieces results in localized heating that softens and plasticizes the workpiece. A volume of processed material is produced by movement of materials from the front of the pin to the back of the pin. During this process, the material undergoes intense plastic deformation and this results in significant grain refinement. (Misha) FSP changes physical properties without changing physical state which helps engineers create things such as “high-strain-rate superplasticity”. The grain refinement occurs on the base material improving properties of the first material, while mixing with the second material. This causes for the base material’s properties. This allows for a variety of materials to be altered to be changed for things that may require other difficult to acquire conditions. The processes branches off of friction stir welding (FSW) which uses the same process to weld two pieces of different materials together without heating, melting, or having to change the materials’ physical state.

Tool

The tool has a crucial part to creation of the final product. The tool consists of two main functions:

1. Localized heating
2. Material flow

The tool at its most simplest form consist of a shoulder, a small cylinder with a diameter of 50 mm, and a pin, a small threaded cylinder similar to a drill. The tool itself has been modified to reduce displaced volume of the metals as they merged together. Recently two new pin geometries have arose:

1. Flared-Trifute - introducing flutes(large carving vertically on the pin)
2. A-skew - the pin axis being inclined to the axis of the spindle.

Testing

Mg based nano-composites

FSP was used to modify a Mg alloy and insert nano-sized SiO2. The test was conducted a total four times with the average grain size varying from 0.5-2μm. This nearly doubled the hardness of the Mg and also increased the super-plasticity. At room temperature, the yield stress of the FSP composites was improved in the 1D and in the 2D specimens signifying a larger resistance of the product metal under high stress conditions without deforming. The tensile strength was shown to increase along with the yield stress.

Benefits

FSP has benefits for when two materials’ would be needed to be mixed. “FSP is a short route, solid state processing technique with one-step processing that achieves microstructural refinement densification and homogeneity”(MA) FSW helps modify materials so that metaling down or changing the material drastically does not have to take place. FSP, for example, can easily change the form of a piece of material as sheets of metal, where before it may have had to be melted down before and put into a mold for it to cool and form. (Smith,Mishra) “The microstructure and mechanical properties of the processed zone can be accurately controlled by optimizing the tool design, FSP parameters an active cooling/heating.”(MA) The same sheet of metal can be modified to fit various situations with the proper modification of the tool. FSP has shown to make metallic alloys bendable as for example an alloy modified with FSP would be able to bend to 30 degrees as before it could only bend to seven.

Negatives

Friction stir processing takes a toll on the metal. Due to the mixture with other materials, the product as a whole suffers a great loss in toughness and ductility. Due to this loss FSP has limited applications in the mechanical fields in which it is currently being used in(aerospace, automobile, etc.)

Uses

The FSP is used when metals properties want to be improved using other metals for support and improvement of the first. This is promising process for the automotive and aerospace industries where new material will need to be developed to improve resistance to wear, creep, and fatigue. (Misha)