Welding and metallurgical weldability of metals

By way of introduction, and to avoid any misunderstanding, it is useful to recall the definitions of the terms which appear in the title of this text. For this purpose, please refer to the document entitled "Terms and definitions used in welding and related techniques" published by Publications de la Soudure Autogène and the Conseil International de la Langue Française [1] .

• Welding: operation consisting in joining two or more constituent parts of an assembly, in such a way as to ensure continuity between the parts to be assembled (continuity in the nature of the materials assembled: metallic material, plastic, etc.), either by heating, pressure or both, with or without the use of a filler material whose melting temperature is of the same order of magnitude as that of the base material.

• Weldability: a metal material is considered to be weldable to a given degree by a given process and for a given type of application, when it lends itself, subject to the precautions corresponding to this degree, to the realization of a construction between the elements of which it is possible to ensure metallic continuity by the constitution of welded joints which, by their local characteristics and the global consequences of their presence, satisfy the properties required and chosen as a basis for judgment.

  The fundamental notion of "continuity in the nature of the materials assembled", and more specifically "metallic continuity", is emerging. This requirement implies the use of interatomic bonding forces of the metallic type (for metals) between the elements to be assembled. These forces require the absence of any foreign body likely to act as a barrier to their action.

  These considerations already allow us to note that :

  • the chemical identity of the assembled metals is not fundamentally necessary;

  • mechanical joining techniques (riveting, bolting, stapling, etc.) or adhesive bonding do not meet the definition of welding.

  In this text, we will look at the following topics in turn:

  • the installation conditions of the metal connection ;

  • the processes used to achieve this bond;

  • the metallurgical phenomena involved and their consequences ;

  • definitions of weldability ;

  • tests to assess metallurgical weldability;

  • the possibility of post-welding actions to improve assembly performance,...