In reply to a message from Roger Payne sent Fri 1 Feb 2013:
As promised, some pictures of an A head from William Mills
with C6733X and WM351 cast in, and DTD424 stamped
afterwards. Also a curious little 12 spoke sun stamp and a
few others.
http://www.jag-lovers.org/snaps/snap_view.php3?id=1359826032
Google turned up a 1955 article in Flight magazine about the
British light alloy aluminium industry, explaining that
DTD424 is a general purpose aluminium casting alloy invented
and patented in 1939 by Percy Pritchard, director of the
Birmingham Aluminium Casting Co., and was used in WW2
throughout the aircraft industry without payment of royalties.
Woldman’s Engineering Alloys says the composition of DTD424
is Silicon 5 percent, Copper 3 percent, Manganese 0.5
percent, balance Aluminum. For sand castings, tensile
strength is 20,200; 12,300 yield strength; elongation is 2.5
percent; Brinell hardness is 65 and it is supposed to be
corrosion resistant.
Another reference on a Vincent motorcycle site claimed the
composition of DTD424 was Silicon 3-6 percent, Copper 2-4
percent, Iron 0.8 percent, Manganese 0.7 percent, remainder
Aluminum.
I wonder if substandard metallurgy, traces of iron in there
would contribute to an increase in corrosion? Has anyone
noticed, is corrosion more frequently seen in a West
Yorkshire head vs a William Mills head?–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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