Aluminium Design and Construction John Dwight

AC.51400
This is another non-heat-treatable alloy. It finds application instead of
AC.44100 when appearance is critical, because of its exceptional corrosion
resistance and suitability for anodizing. But, against this, it has inferior
fluidity, ruling out its use for thin intricate castings. Good foundry
practice is important.
AC.42000
This heat-treatable alloy, in the T6 condition, is chosen when higher
strength is needed. Like AC.44100, it has excellent fluidity and good
corrosion resistance. Also it is more readily machined.
4.6 ALLOYS USED IN JOINTS
4.6.1 Fastener materials
Chapter 11 includes design data on four typical alloys for use as fasteners,
namely 6082, 6061, 5154A and 5056A. The first three have already been
mentioned above (Section 4.3). The fourth is an alloy containing a nominal
Mg 5.0 and Mn 0.35% that produces fasteners as strong as 6082. Because
of its high magnesium content it is unsuitable for prolonged use in hot
environments.
Stronger alloys are employed for the fasteners used in aeronautical
construction. These can be in 2xxx-series alloy (T4 or T6 temper), or in
a strong 7xxx-series material such as 7075-T6. In the USA strong fasteners
in these materials also find use outside the aero field.
4.6.2 Weld filler wire
Alloys for use as welding wire are divided into four types (Section
3.3.4). Table 4.8 lists, with their nominal compositions, the alloys of
each type that are covered in BS.8118.
4.7 CORROSION
4.7.1 Corrosion of exposed surfaces
Any aluminium surface exposed to air develops a thin oxide film, which
is hard, chemically stable and tightly keyed to the metal. Though very
thin (typical thickness 0.005 mm), this layer prevents further oxidation.
When damaged, it immediately reforms, provided oxygen is available,
and it is this that gives aluminium its good durability.
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