why do manufacturers use "magnesium" in camera bodies

Just wondered, in an idle moment, why camera bodies are commonly

cast from a magnesium alloy? What is it about that metal that makes

it superior for this type of application?

I'm no metallurgist, but Canon's own description is "a <i>super tough</i> and <i>light weight</i> magnesium alloy body".

Alloying magnesium and something like aluminum gives a strong metal with a low cost compared with a body made from something cool and expensive like titanium. Also the magnesium can be machined, so they'll start with a block of the stuff and machine the camera body, making it easier for production and reducing manufacturing costs. Another popular application for magnesium alloy parts is in car production, where cutting costs is even more important than in cameras.

1. Magnesium is an element. As such, the first "M" is always a capital letter.

 

 

2. Magnesium is 1/3rd lighter than Aluminum, and, if I understand metals correctly, is the lightest metal that can be used in structural components.

 

 

3. When alloyed, Magnesium takes well to casting (e.g. structural body parts for cameras).

Magnesium is much lighter than Titanium.

Titanium is as strong as steel but almost as light as aluminium. It is also very expensive and difficult to work with. Magnesium is lighter still and has working properties closer to aluminium. It can be cast, extruded and milled. With better cameras weight vs strength is critical. With cheaper cameras the issue becomes strength vs cost; hence plastic.

Magnesium is only about 50% as dense as aluminum (not capitalized!), but not as strong. For the same strength, magnesium parts are about 1/3 lighter than aluminum. Both magnesium and aluminum can be cast and machined easily.

 

Titanium is nearly twice as dense as aluminum, but is extremely strong and can be fabricated into structures about 20% lighter than aluminum. Titanium is extremely difficult to fabricate because of its strength and hardness, and is generally limited to sheets, tubing and simple castings. With a melting point over 1700 degrees C (aluminum and magnesium about 650C), it is highly resistant to heat, fatigue and oxidation, as in the skin of military aircraft. Its use in cameras has been limited to shutters, prism covers and base plates.

Note that magnesium burns in air. In fact early "flash powder" was, I think, magnesium.

 

It's difficult to ignite in a large block, but once it gets going, pretty much nothing will stop it. It will happily burn in nitrogen, carbon dioxide and water.

 

Magnesium/aluminum alloys are strong, light, inexpensive, easy to machine and non-combustible!

In addition to all of the above listed attributes, magnesium is also very easy to cast very precisely with relatively low cost tooling, and is very stiff for it's weight. This stiffness makes for a very solid feeling camera at a lighter weight than aluminum or titanium. A titanium camera of equal strength and weight would feel very flexy. A titanium camera of equal stiffness would be very heavy ( and super strong )

 

VW and Porsche both used to use magnesium for their engine blocks for all these reasons, and their was even a ski boot made of magnesium in the 70s called the Dale boot.

I have a Canon Digital Rebel which has a plastic body at first this didn't cause me any problems and it was fine. Until I put a big 70-200 f2.8 lens. now it feels like the whole camera flexes from the weight of the lens.

Magnesium alloys are very easy to machine with standard tools. Titanium is a PITA. It is very hard to machine. It has a tendency to move around.

 

At one time I had a machine shop and the machinists hated working on titanium. We had to make very high precision parts, and had to be very careful with tool pressures as the titanium would compress very slightly under pressure. When the part was QC'd it didn't match the print because the metal had expanded back out.

 

This meant we had to develop programs that took into account the amount the metal would deform under "hogging" passes, work on another area of the piece and then come back and do very light pressure cleanup passes.

 

Tooling was expensive. We tried tool steel, carbide, ceramic, titanium nitride coated, and finally settled on cobalt-steel alloy tools. All of the others either wouldn't make the finish required, or would dull rapidly.

 

Magnesium alloy on the other hand machines much like aluminum with the caveat that the chips can catch on fire. A flood of coolant to keep the part/cutting tool lubricated and cool and it machines like 'butta.

Perhaps the single best reason is that a magnesium alloy resists corrosion to a degree that aluminum or steel do not. I think that is the number one reason why it's so popular in the camera market.

To Eric (and others) - I did a little research on the capital letter thing for elements, as the stated rule seemed a little questionable. What I found is that when you use the whole name (such as magnesium), you do NOT need to capitalize the first letter of the word. When you use the abbreviation, though, the first letter of the abbreviation is capitalized. Example for magnesium is Mg. Reference site: http://scidiv.bcc.ctc.edu/wv/1/0001-05-element-symbols.html

 

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So if the electronics short out & the camera catches on fire it will burn with a really bright flame. Magnesium makes for great flares.