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A question for metallurgists


#1

While I’m trying to decide what to cast some plaques out of, I found
an interesting melting temperature according to this chart.

http://www.ganoksin.com/gnkurl/ep80gd

I want to use some kind of bronze since plain aluminum patinas will
fade.

(This project if for my palm tree arboretum project I mentioned).

According to The Engineer’s Tool Box on the above link,
Aluminum-Bronze alloy melts at only 1215 F. They can’t possibly be
talking about commonly used alloys of Aluminum-Bronze that I can find
because any Aluminum Bronze I know of has typical bronze melting
temperatures of over 2000 F.

I thought Aluminum-Bronze must be over 90% copper or the
Aluminum-Bronze would be too brittle? There are no 50/50 Aluminum
Bronze mixtures that would not be brittle. But to have a melting
temperature of only 1215 are they talking about an Aluminum Bronze
that is over 90% Aluminum and they just add a little copper?

Now if that’s the case, I am interested. (The lower melting
temperature would make my set up for casting large plaques easier)

If this is what they are talking about, (A large percentage of
aluminum with just a little bit of copper), will this 10 to 12% of
copper be enough for me to chemically patina and stay an interesting
color outdoors?

Thanks for any help.


#2

The aluminium bronze we used to sell was predominantly aluminium
with a little copper. and a few other elements thrown for different
purposes. Hard as the hobs of hell. CIA


#3
According to The Engineer's Tool Box on the above link,
Aluminum-Bronze alloy melts at only 1215 F. 

It is a typo.

James Binnion
James Binnion Metal Arts


#4

I wouldn’t think that link is correct. If you want a reliable alloy
use a silicon bronze alloy. The aluminum alloys you are referring to
are not really suited for small studio castings unless you have
platinum torches /high heat capabilities. The silicon bronzes are
about 95% copper, and 4% silicon, or a harder bronze with 92% copper
and equal parts zinc and Silicon (bronze “H” - melt 1600-1780
Fahrenheit and pour 1825-2050 F though less ductile than the Si
Bronze “Everdure"brand” Bronze D" with a higher melt:pour temp of
1590- 1790 F/1850 up to 2250 F).The harder bronze is lighter in
colour than Si bronze but less finishing is required and greater
detail is possible in castings, which is a trade off in ductility-
the greater ductility the better it will take a patina. or that’s the
theory as each patina is different and bottled branded patinas are
designed for consistent results by simply brushing them on (and
following any further instructions). Both silicon bronze casting
pieces run about ten dollars US from most sources in a ten lb.
quantity or better (cheapest in 50 lb. lots, but shipping is
significantly increased if you aren’t near a vendor from which you
can pick them up at a sales counter).

I am unclear what you mean by “aluminum patinas” - Any patinas I have
ever worked with can be put on any metal by various methods from
fuming to painting to direct colouration and then sealing. rer