The two general requirements for forming good friction welds are, first, that the materials to be joined can be forged and, second, that the materials can generate friction at the weld interface. The relative ease of friction welding metals to themselves is related to the matching properties at the weld interface.
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Requirements of forming good friction welds:
- The first requirement eliminates similar-metal welds in brittle materials such as ceramics, cast irons, and cemented carbides. However, ductile materials can sometimes be joined to these materials.
- The second requirement eliminates materials that contain alloying that provide dry lubrication. Free-machining additives to steel, graphite-containing alloys such as cast iron, and lead alloys may suffer from this requirement.
Almost all other metal alloys can be welded to themselves by FRW techniques. Near full-strength metallurgical bonds can be produced for a very wide range of similar-metal alloy friction welds.
The microstructure and mechanical properties of inertia-welded similar-metal joints for the following alloys can be found in the sources listed:
(A) MOMENT OF INERTIA OF THE FLYWHEEL.
(B) TOTAL SHORTENING OF THE WORKPIECES DURING WELDING.
(C) SUM OF HEATING TIME PLUS WELDING TIME.
- The relative ease of friction welding metals to themselves is related to the matching properties at the weld interface.
- Because the materials properties are matched, heat is distributed uniformly on both sides of the joint, and the deformation characteristics are identical on both sides of the joint.
- This results in symmetric welds with good properties. In general, the process variables do not vary significantly for different alloys within a given class of materials.
- However, there can be a significant variation in processing variables between different classes of materials
- Because FRW generates localized heating at the interface, the HAZ is subject to rapid cooling due to heat transfer to the cold base metal. This rapid quenching may sufficiently alter the mechanical properties of the base metal in the HAZ region to require post weld heat treatment. For example, in order to restore ductility, stress relieving or tempering may be required to friction weld steels with hardenability greater than that of AISI 1035
- In addition, age-hardenable alloys will lose strength in the HAZ during welding and may require postweld solution heat treating and/or postweld aging to restore their strength. Other alloys, such as those that obtain their strength from cold working, will lose strength in the HAZ of the weld, and their properties cannot be restored with postweld treatments.