Tim Wescott wrote:



If I'm not mistaken, it's not that the work won't get hot enough to glow,
it's that aluminum is never emissive enough in the visible wavelengths
for it to glow. If you watch aluminum casting, you'll see that the
crucible is glowing a dull red, even though the aluminum inside is
shiny. If the aluminum were "black" (meaning, if it were emissive), it'd
be glowing that same dull red.

Hmmm! Very interesting! Well, aluminum has a high specific heat, so it
takes a lot of energy to raise the temp. So, it is possible that the
crucible gets hotter than the melt. I've watched some guys do aluminum
pours, and if you get the aluminum too hot, you get a lot of dross, so that
is to be avoided. Also, when welding, you want the work JUST hot enough to
fuse. Get it too hot, and it ends up on the floor. Due to the high thermal
conductivity of aluminum, the range between welding and melting the whole
piece is REALLY small. Much harder than with steel, for instance.

Jon