Page 12 - Welding of Aluminium and its Alloys

4 The welding of aluminium and its alloys

1.3 Warrior armoured fighting vehicle (AFV) utilising Al-Zn-Mg alloys.
Courtesy of Alvis Vehicles.

processes. It is hoped that this book will go some way towards giving the
practising shop-floor engineer an appreciation of the problems of welding
the aluminium alloys and guidance on how these problems may be over-
come. Although it is not intended to be a metallurgical textbook, some
metallurgical theory is included to give an appreciation of the underlying
mechanisms of, for instance, strengthening and cracking.

1.2 Characteristics of aluminium

Listed below are the main physical and chemical characteristics of
aluminium, contrasted with those of steel, the metal with which the bulk of
engineers are more familiar.As can be seen from this list there are a number
of important differences between aluminium and steel which influence the
welding behaviour:

• The difference in melting points of the two metals and their oxides.The
oxides of iron all melt close to or below the melting point of the metal;
aluminium oxide melts at 2060°C, some 1400°C above the melting point
of aluminium. This has important implications for the welding process,
as will be discussed later, since it is essential to remove and disperse this
oxide film before and during welding in order to achieve the required
weld quality.