On Nov 29, 10:04*am, wrote:

Greetings Dan,
Cast tooling plate is good for stability. So it won't move like a
similar wrought plate made from 6061. Threads pull out easier than
6061 so inserts are comminly used. The "precision machined" surface
actually isn't unless someone machined it after buying the plate. The
surface looks machined because the aluminum is cast against a machined
surface. I used to wonder how the factory got that shiny machined
surface when I never could quite match it myself. I figured they maybe
used diamond cutters running dry at very high speeds to save time.
Then I found out the stuff isn't machined afterall.
Eric

I did some looking around on the internet. And found this at
http://www.tquigley.com/mic-6.htm which says they do take off a few
thousandth.
The piece I have still has the protective film on it and looks as if
it was machined with some kind of big rotating cutter.

Dan


Ultimately, it was a process pioneered

by Hunter Engineering that led to today’s most advanced cast aluminum
plate. The

company, a forerunner of Alumax, developed a horizontal, continuous
caster to produce individual plate thicknesses. Alumax refined the
technology to bring dimensional control and stability to the next
level. The original product (named CC-70) has evolved to become the
state-of-the-art material known as Mic-6® Precision Machined Cast
Aluminum Plate. Alcoa, which acquired Alumax in 1998, now produces and
markets Mic-6® Precision Machined Cast Aluminum Plate at its Mill
Products facility in Lancaster, Pennsylvania.

The Mic-6® manufacturing technology involves a patented continuous
casting technique that allows precise casting to near net thickness -
the “as-cast” thickness is only a few thousands of an inch greater
than the final plate thickness. Using a continuous flow of molten
aluminum, casting speed and the rate of solidification are tightly
controlled. A spinning nozzle inert filtration (SNIF) unit provides
additional filtration and degassing, virtually eliminating internal
defects. Proprietary equipment removes heat from both plate surfaces
at a carefully balanced rate so thermal gradients are stabilized. As a
result, grain size and distribution are identical on both plate
surfaces!

This unique casting process gives Mic-6® a granular structure that
resembles a honeycomb (see Figure 1). In the solidification process,
aluminum (which has a higher melting point than the alloying
ingredients) forms the cell core with alloy elements concentrated
between the cells. This segregation of low and high melting point
compositions imparts characteristics that make Mic-6® highly
machineable, producing small, uniform chips in a variety of high speed
operations.

After casting, the Mic-6® plate is subjected to thermal treatment in
excess of 700 degrees F for up to 10 hours. The resulting product is
fully stress relieved (fully annealed), eliminating stresses that
developed during casting as well as any heat-treating effects that may
have occurred during or after solidification. The material is “dead
soft”, comparable to the “O” temper designation in wrought aluminum.

These steps result in a significant design benefit for Mic-6®…there is
no decrease in mechanical properties when the plate is exposed to
elevated temperatures. This is true for both extended periods of high
temperature and cyclical exposure (even an infinite number of thermal
cycles). Once the Mic-6® plate is returned to room temperature, its
tensile properties are the same as they were prior to exposure. There
is no over-aging, which occurs in solution heat-treated plate, or the
partial annealing that is characteristic of strain-hardened material.
Accordingly, Mic-6® is recommended for applications where high
temperature conditions would be a problem for wrought aluminum
tempers.