Page 76 - Welding of Aluminium and its Alloys

66 The welding of aluminium and its alloys

4.9 Typical pickling shop. Courtesy of R. Andrews.

thoroughly cleaned of any foreign metals before being used on aluminium
alloys.

4.7 Cleaning and degreasing

Components for welding may be flat, preformed, sheared, sawn or milled
to give the desired shape or to provide the weld preparation. Lubricants
used during these processes must be removed if weld quality is to be main-
tained. Degreasing may be accomplished by wiping, brushing, spraying or
vapour degreasing with commercially available solvents. This is best done
before any mechanical cleaning takes place. Mechanically cut edges may
carry burrs along the cut edge that will trap dirt and grease. These burrs
should therefore be removed from weld preparations by scraping with a
draw tool – do not wire brush only as this may fail to remove them com-
pletely. Scraping is also an excellent method for removing the oxide film.
Stainless steel wire brushes, stainless steel wire wool or files may also be
used to remove the oxide. As mentioned above in Section 4.6, under no
circumstances should carbon steel, brass or copper brushes be used. Make
sure that any cleaning tools are segregated and are used only on aluminium,
otherwise cross-contamination can occur.
In certain cases, particularly when striving to achieve freedom from
porosity, chemical cleaning or pickling may be required. A pickling shop is
illustrated in Fig. 4.9 and a schedule of chemical cleaning treatments is given
in Table 4.4.