Weldability of metal matrix composites (MMCs)

The most significant property gains are associated with long-fibre materials which are the most expensive to produce and few applications outside space and defence can bear the associated material costs. High volume applications are for particulate reinforced alloys for which relatively modest property enhancement is effected.

Most materials are unsuitable for fusion welding techniques because their carefully engineered structures are destroyed if melting occurs. Indeed, even elevated temperature exposure will degrade some materials. Thus, the most satisfactory joining techniques are often those which are carried out at lower temperatures, i.e. adhesive bonding, brazing or solid phase joining procedures, such as friction welding and diffusion bonding. Friction welding has proved particularly successful for joining particle reinforced aluminium alloys.

One of the exceptions to the general rule is aluminium alloys reinforced with alumina particulate. Alumina is stable in molten aluminium and MIG welding has been successfully applied to structures such as bicycle frames. The latter is a typical application for this class of materials since, in sporting goods, premium performance can command premium price and advanced technology can be a selling point rather than a cost burden.

Packaging for electronic devices is another area where the costs associated with the production of MMCs can be justified. A high volume fraction of silicon carbide particulate creates a packaging material which is matched in thermal expansion coefficient with the silicon devices. When these packages must be hermetically sealed, appropriate bonding or brazing technology must be applied.

The most relevant industry sectors are:

Aerospace
Defence
Sporting and Leisure goods
Automotive