Page 19 - Welding of Aluminium and its Alloys

Welding metallurgy 11

Weld face Heat affected zone

Weld toes Single sided butt weld
face and
Weld root
passes or Root pass or
runs
penetration bead

st
1 side welded

Fusion Double sided weld
boundary

nd
2 side welded

Weld toe
Weld
face
Root Fillet weld

2.1 Definition of weld features.

2.2.1 Structure of metals

Before discussing the principles by which metals achieve their mechanical
strength it is necessary to have an appreciation of their structure and how
these structures can be manipulated to our benefit. The simple model of an
atom is of a number of electrons in different orbits circling a central nucleus.
In a metal the electrons in the outer orbit are free to move throughout the
bulk of the material. The atoms, stripped of their outer electrons, become
positively charged ions immersed in a ‘cloud’ of negatively charged elec-
trons. It is the magnetic attraction between the positively charged ions and
the cloud of mobile, negatively charged electrons that binds the metal
together. These atomic scale events give metals their high thermal and