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Introduction to the welding of aluminium
Introduction
The existence of aluminium (Al) was postulated by Sir Humphrey Davy
in the first decade of the eenth century and the metal was isolated in
1825 by Hans Christian Oersted. It remained as somewhat of a labora-
tory curiosity for the next 30 years when some mercial pro-
duction began, but it was not until 1886 that the extraction of aluminium
from its ore, bauxite, became a truly viable industrial process. The method
of extraction was invented simultaneously by Paul Heroult in France
and Charles M. Hall in the USA and this basic process is still in use today.
Because of its reactive nature aluminium is not found in the metallic
state in nature but is present in the earth’s crust in the form of different
compounds, of which there are several hundreds. The most important
and prolific is bauxite. The extraction process consists of two separate
stages, the first being the separation of aluminium oxide, Al2O3 (alumina),
from the ore, the second the electrolytic reduction of the alumina at
between 950°C to 1000°C in cryolite (Na3AlF6). This gives an aluminium,
containing some 5–10% of impurities such as silicon (Si) and iron (Fe),
which is then refined either by a further electrolytic process or by a
zone-melting technique to give a metal with a purity approaching %.
At the close of the twentieth cent