WO Mounting Plate

[Visionary]

Today I took delivery of a magnificently machined William Optical Mounting plate. Once out of it's packaging it felt oddly heavy, far too heavy to be Aluminium.
I check on the WO website, and the plate was described as Anodised Aluminium. My son an undergraduate engineer immediately "poo-whoed" the suggestion that the plate was Aluminium, suggesting it is either stainless steel or machine steel.
Does the ultra-high grade Aluminium used by WO, weigh more than garden variety steel? Is there an alloy of Aluminium that weights more than standard Aluminum?

[pdalek]

My plate has mass 540 g and volume 200 ml by displacement (or 224 ml less holes -> ~ 200 by physical measurement)
Density works out at 2.7 which is the expected value for pure aluminium.

It just seems to be heavier than you expect.

[Visionary]

My Son is a pedant, he looked into it further and came up with a possible explanation

Aluminum bronze (3-10% Al) 7700 - 8700 Density (kg/m3)

Steel 7850 Density (kg/m3)

That sort of makes some sense and explains the weight of the mount. He lifted the weight/density description from the Engineering Toolbox (website) http://www.engineeringtoolbox.com/metal-alloys-densities-d_50.html
The weight of the mount is explained with Bronze as an alloy. The alloy must contain a heap of Bronze. Given OW's description, this seems to be the only sensible explanation.

[Dennis]

I have a couple of these from say, 5 or 6 years ago and have drilled and tapped holes in them to fit accessories. The material certainly behaved like aluminium, soft, easy to drill and tap.

Cheers

Dennis

[Visionary]

Denis, I have not drilled the plate but it sure is tricky. I think I will take the scope off and weight the thing I worked in fishing tackle, so I have handled an seen machined blocks of aluminium, the weight of this material has the heft of steel.
I think I will email WO and see what there answer is...
Cheers
David

[SteveInNZ]

As an engineer, I would have hoped that your son would have weighed and measured the offending piece of metal but I don't see that mentioned.

Steve.

[Visionary]

Steve,

He is in the full flower, a third year undergraduate. In his defence, his first impulse was to grab a magnet to determine ferrous/non ferrous he called it for steel prior to the magnet test.
My money is on the alloy of Aluminium-bronze, apparently this alloy is used for precision milling and applications where the customer can withstand the cost, it really does sound like an Astro application for the alloy. In addition the high bronze content would certainly explain the weight of the mounting plate.

David