Coating aluminum

6061 and 2024 are not pure aluminum. In order to obtain the desired
strength
properties, other metals are added to the aluminum. I believe 2024 has
something of the order of a couple percent of copper. The surface will not
be pure aluminum oxide, since there are "impurities" within the metal. You
are now open to pitting corrosion as well as granular corrosion.


2024

Cu 3.8 - 4.9
Mg 1.2 - 1.8
Mn 0.30 - 0.9
Fe = 0.50
Si = 0.50
Zn = 0.25
Zr+Ti = 0.20
Total Other = 0.15
Ti = 0.15
Cr = 0.10
Other Elem = 0.05
Al Remainder



6061

Mg 0.40 - 0.8
Si 0.30 - 0.6
Fe = 0.35
Cu = 0.25
Cr = 0.20
Mn 0.05 -0.20
Total Other = 0.15
Zn = 0.15
Ti = 0.10
Other Elem = 0.05
Al Remainder

All compositions in wt%.

"alclad" sheets have a thin layer of pure aluminium on the surface to
improve corrosion resistance.

see http://aluminium.matter.org.uk/aluse...ion_browse.asp for
corrosion and anodizing properties.


--
Geoff
the sea hawk at wow way d0t com
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