Page 177 - Welding of Aluminium and its Alloys

160 The welding of aluminium and its alloys

8.11 Conventional rotary motion friction welding. Courtesy of TWI Ltd.

immediately the vapour has dispersed. This can be done extremely rapidly,
the weld pool remains molten and cavity formation is avoided. Although
some of the alloying elements, i.e. magnesium and zinc, are lost, this is gen-
erally insufficient to cause a loss of strength. Elongated cavities in the fade-
out region may be produced, particularly in circular components where a
run-off tab cannot be used. These may be avoided by careful control of the
travel speed and beam fade-out.
The non-heat-treatable alloys can be welded fairly readily without the
addition of filler wire but hot cracking problems may be encountered in the
more sensitive grades and in the heat-treatable alloys.As with laser welding,
wire additions may help. Heat affected zones are small and strength losses
are less than would be experienced in a similar thickness arc welded joint.

8.5 Friction welding

Unlike the other processes covered in this book friction welding is a solid
phase pressure welding process where no actual melting of the parent metal
takes place. The earliest version of the process utilised equipment similar
to a lathe where one component was held stationary and the other held in
a rotating chuck (Fig. 8.11). Rubbing the two faces together produces suf-
ficient heat that local plastic zones are formed and an end load applied to
the components causes this plasticised metal to be extruded from the joint,