Page 10 - Welding of Aluminium and its Alloys

2 The welding of aluminium and its alloys

alloys finding a ready use in the fledgling aeronautical industry. Since that
time a large range of alloys has been developed with strengths which can
match that of good quality carbon steel but at a third of the weight.A major
impetus to the development of aluminium alloys was provided by the two
World Wars, particularly the Second World War when aluminium became
the metal in aircraft structural members and skins. It was also in this period
that a major advance in the fabrication of aluminium and its alloys came
about with the development of the inert gas shielded welding processes of
MIG (metal inert gas) and TIG (tungsten inert gas). This enabled high-
strength welds to be made by arc welding processes without the need for
aggressive fluxes. After the end of the Second World War, however, there
existed an industry that had gross over-capacity and that was searching for
fresh markets into which its products could be sold. There was a need for
cheap, affordable housing, resulting in the production of the ‘prefab’, a
prefabricated aluminium bungalow made from the reprocessed remains of
military aircraft – not quite swords into ploughshares but a close approxi-
mation! At the same time domestic utensils, road vehicles, ships and struc-
tural components were all incorporating aluminium alloys in increasing
amounts.
Western Europe produces over 3 million tonnes of primary aluminium
(from ore) and almost 2 million tonnes of secondary or recycled aluminium
per year. It also imports around 2 million tonnes of aluminium annually,
resulting in a per capita consumption of approximately 17kg per year.
Aluminium now accounts for around 80% of the weight of a typical civil-
ian aircraft (Fig. 1.1) and 40% of the weight of certain private cars. If pro-
duction figures remain constant the European automotive industry is
expected to be consuming some 2 million tonnes of aluminium annually by
the year 2005. It is used extensively in bulk carrier and container ship super-
structures and for both hulls and superstructures in smaller craft (Fig. 1.2).
The new class of high-speed ferries utilises aluminium alloys for both the
super-structure and the hull. It is found in railway rolling stock, roadside
furniture, pipelines and pressure vessels, buildings, civil and military bridg-
ing and in the packaging industry where over 400000 tonnes per annum is
used as foil. One use that seems difficult to rationalise in view of the general
perception of aluminium as a relatively weak and soft metal is its use in
armoured vehicles (Fig. 1.3) in both the hull and turret where a combina-
tion of light weight and ballistic performance makes it the ideal material
for fast reconnaissance vehicles.
This wide range of uses gives some indication of the extensive number
of alloys now available to the designer. It also gives an indication of the
difficulties facing the welding engineer. With the ever-increasing sophis-
tication of processes, materials and specifications the welding engineer
must have a broad, comprehensive knowledge of metallurgy and welding