Page 79 - Welding of Aluminium and its Alloys

68 The welding of aluminium and its alloys

Once degreased and cleaned the parent material should be welded within
a short period of time; typically four hours would be regarded as reason-
able. The component must be maintained in a clean condition during this
time and this may require the item to be covered with polythene sheets or
brown paper. If the item is left standing overnight the joints may require
an additional cleaning operation so it is advisable to clean only those parts
that can be welded within a four or five hour production period.
There are a couple of points concerning cleanliness that are worth men-
tioning. If the chemical cleaning has been extremely good then it is possi-
ble to leave the components for a longer period of time, perhaps overnight
if the storage conditions are clean and dry. It has also been noticed that
when the items are ‘super clean’ the TIG or MIG welder can experience
arc starting and stability problems. The reason for this is not clear but is
probably associated with the complete absence of any oxide. It is thought
that a small amount of oxide assists in the formation of an active anode
spot, resulting in a more stable arc.
The aluminium fabrication area ideally should be separated physically
from other fabrication areas. For example, dust from activities such as
grinding, settling on the surface will cause problems, particularly if this is
from the grinding of steel items in adjacent bays. Aluminium and steel
should never be welded in the same welding booth. It cannot be empha-
sised too strongly how important attention to cleanliness is if sound, defect-
free welds are to be made consistently.