Metal Foams: A Design Guide

15.3 Joining of metal foams
Cutting, finishing and joining 195
Metal foams can be soldered and welded. Foams have a cellular structure
resembling, in some ways, that of wood. Because of this they can be joined
in ways developed for wood, using wood screws, glue joints or embedded
fasteners. Figure 15.1 summarizes joining methods.
Wood screws
Gluing
Glue line
Embedded fastening
Solder
Soldering/brazing
Welding
Figure 15.1 Ways of fastening and joining metal foams
Welding, brazing and soldering
Welding and brazing are best used for foams with integral skins. Studies of
laser welding (Burzer et al., 1998) show promise, but the technique requires
careful control. Brazing of Al-based foams with aluminum–eutectic alloys
is practical. The soldering of aluminum foams requires a flux to remove the
oxide film. If the flux penetrates the foam it causes corrosion, so soldering is
only practical for sandwiches or skinned structures, restricting the solder to
the outer surface of the skin. Soldered joints weaken the foam, which fails at
a stress less that the tensile strength of the foam itself.
Adhesives
Foams can be glued with the same adhesives used to bond the base metal
(Olurin, et al., 1999). The glue joints are usually stronger than the foam itself.
There are some drawbacks: low thermal stability, mismatch of expansion coefficient
and the possible creation of a thermal and electrical isolation barrier.
Provided these are not critical to the design, adhesives (particularly epoxies)