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Stainless magnesium breakthrough bodes well for manufacturing industries

By

August 29, 2013

2.5 liter V6 magnesium alloy engine block (Photo: US Department of Energy)

2.5 liter V6 magnesium alloy engine block (Photo: US Department of Energy)

Image Gallery (2 images)

Magnesium alloys are very attractive for a range of weight-sensitive applications. They have the largest strength-to-weight ratio of the common structural metals, are lighter than aluminum and are particularly favored for being easy to machine and for their ability to be die cast to net shape. Unfortunately, magnesium alloys tend to corrode too easily. A team at Monash University in Australia has now discovered a novel and potentially game-changing approach to the problem: poisoning the chemical reactions leading to corrosion of magnesium alloys by adding a dash of arsenic to the recipe.

Magnesium alloys are of great interest as lightweight replacements for aluminum, titanium, and steel components in a range of transportation and aerospace applications. However, such alloys corrode easily, and this often prevents their use as replacements for noncorroding metals, particularly in applications requiring high reliability over a range of environments. As a result, the use of magnesium alloys at present is less than a million tons per year, while nearly 50 million tons of aluminum alloys are used each year.

Research and development carried out over the past decade have solved certain problems presented by magnesium alloys. Their tendency toward high-temperature creep was tamed by inclusion of scandium and gadolinium, and their flammability has been greatly reduced by introducing a small amount of calcium into the mix.

Corrosion resistance in magnesium alloys has not improved to the same degree. The main discovery is that the presence of iron, nickel, copper, and cobalt in a magnesium alloy strongly activates corrosion. This is due to their low solid solubility limits (meaning that above a very small percentage they precipitate out as intermetallic compounds within the alloy structure) and the fact that they have the right electrochemistry to behave as active cathodic sites that reduce water while causing the loss of magnesium from the alloy.

If a magnesium alloy has small enough quantities of these metals, it will have improved corrosion resistance. Also, the presence of iron can be overcome by the presence of a larger amount of manganese. Maintaining such precise control over the composition of structural magnesium alloys, unfortunately, forces the price skyward, and doesn't really solve the corrosion problem.

Corrosion chemistry with and without arsenic as cathodic poison (Image: Monash University)

Led by Associate Professor Nick Birbilis, the Monash team attempted to apply an additive known as a cathodic poison to a standard magnesium structural alloy. Cathodic poisons act by capturing atomic hydrogen within the structure of a metal. This prevents the formation of free hydrogen gas which is required to balance the corrosive chemical processes. A number of alloying elements, including arsenic, antimony, sulfur, selenium, and tellurium, are known to act in this manner in other alloy systems.

The result was that addition of about one-third of a percent of arsenic to the magnesium alloy reduced its corrosion rate in a salt solution by a factor of nearly ten. In this initial study the intent was to prove the principle of the use of cathodic poisoning. Prof. Birbilis' lab is currently working with corporate sponsors on developing a series of commercially practical stainless magnesium alloys.

"This is a very important and timely finding," says Prof. Birbilis. "In an era of light-weighting for energy and emissions reductions, there is a great demand for magnesium alloys in everything from portable electronics to air and land transportation. Magnesium products are rapidly evolving to meet the demands of industry, but presently are hindered by high corrosion rates. The arsenic effect we discovered is now being trialed as a functional additive to existing commercial alloys. Our breakthrough will help develop the next generation of magnesium products, which must be more stainless.”

Considering the enormous impact of stainless steels on our society, the game-changing potential of stainless magnesium is clear.

The University of Wales and CSIRO also took part in the research, the findings of which are published in the journal Electrochemistry Communications.

Source: Monash University

About the Author
Brian Dodson From an early age Brian wanted to become a scientist. He did, earning a Ph.D. in physics and embarking on an R&D career which has recently broken the 40th anniversary. What he didn't expect was that along the way he would become a patent agent, a rocket scientist, a gourmet cook, a biotech entrepreneur, an opera tenor and a science writer.   All articles by Brian Dodson
24 Comments

Interesting stuff. Wonder whether the arsenic becomes less soluble when alloyed with the magnesium. And could you get arsenic poisoning if you cut yourself on a sharp corner made from this alloy? Might be a way to lock arsenic up into a non-toxic form. May sound strange, but nickel and chromium are toxic, and much less so when locked up in stainless steel alloys.

MBadgero
29th August, 2013 @ 05:17 am PDT

The foundry workers would probably get sick.

Anthony Parkerwood
29th August, 2013 @ 05:26 am PDT

This is indeed a potential game changer. Outboard motors, marine gas turbines (aircraft use mag but marine has to use aluminium) even gas weed trimmers would benefit. The list is really endless.

Grumpyrelic
29th August, 2013 @ 06:26 am PDT

"poisoning the chemical reactions leading to corrosion of magnesium alloys by adding a dash of arsenic to the recipe" ...and anybody who uses a grinder on it. This sounds like H&S nightmare for anyone processing it.

squigbobble
29th August, 2013 @ 06:37 am PDT

This is a great development. I have one question, can this alloy be extruded into structural components like aluminum?

Ken Tuck
29th August, 2013 @ 06:53 am PDT

@squigbobble, this is also true for sawing, milling or grinding stainless steel. That's why they give you the MSDS when you buy it in stock forms (sheet, tube, rod, etc.).

MBadgero
29th August, 2013 @ 07:25 am PDT

Would I want an engine block made of magnesium? I don't know how hot it would have to get to ignite, but I recall magnesium fires as being quite a thing.

limbodog
29th August, 2013 @ 07:31 am PDT

Promising discovery ...

Sergius
29th August, 2013 @ 08:25 am PDT

Cathodic poisoning sounds like a surface finishing process after processing via machining, casting, stamping and extruding..

Even lighter electric motors?

Will it allow a 3d laser sintered printing process?

What are the best alloys?

Immersive CAD machining?

George McGregor Wilson
29th August, 2013 @ 09:08 am PDT

@limbodog

Magnesium fires are quite a thing, but you have to have a very high surface area (like magnesium tape or shavings) to ignite it. As a block I believe it would melt before it burned. Aluminum burns, too, but so far as I know no Al engine blocks have spontaneously combusted.

One-third of one percent is 0.00333 repeating. That's not a whole lot of anything. I imagine if you worked around it long enough you might accumulate significant Arsenic exposure. Arsenic is encountered in copper smelting so it isn't as if industry doesn't have experience working with it in a (hopefully) safe manner.

PDS
29th August, 2013 @ 10:39 am PDT

Any machining on this material should be done with a soluble oil mixture which will control even the finest of grinding dust. Add ventilation and there is no issue. Conventional milling or lathe work would not be an issue provided you know what you are doing with a machine tool and don't attack a material such that it gets exceedingly hot. That is where amateurs get in trouble.

Our machinists do mill and lathe work on Berylium Copper often and it does not present a problem provided using a sharp tool and the correct speeds and feeds.

Any supplier that does grinding is going to have the ability to control dust to a safe level. We have ceramics containing BeO ground all the time.

All alloys have something in them that is bad for a human if exposed to that substance. Chromium is a prime example. Zinc is another. Yes, zinc is something that we all need but you can also get too much. Machinists work around these materials all day everyday yet you don't see them having any greater rate of exposure then anyone else.

I take it most of you guys have never worked on a machine more then just in high school metal shop. If you aren't qualified to comment on a subject you probably shouldn't!

Donzie
29th August, 2013 @ 11:01 am PDT

Based on my math if you made a water valve out of this stuff three pounds of it would have to dissolve into the average water consumption per year to reach the EPAs .01 ppm safety level.

n2liberty
29th August, 2013 @ 12:47 pm PDT

I think the arsenic in magnesium alloy will be less of o problem than mercury in light bulbs.

@ limbodog

What is the important difference between having an engine die a quit thermal death and having an engine die a spectacular thermal death.

Besides as the article mentioned a bit of calcium added to the mix reduces the problem.

Slowburn
29th August, 2013 @ 01:01 pm PDT

Arsenic is not as poisonous as most people think, that is people can handle trace amount of it with little side effects. I would be interested in how much -or how little- arsenic is required to make the metal corrosion resistant.

Johnny Kang
29th August, 2013 @ 05:58 pm PDT

Potentially a brilliant idea! Health fears have been covered before this comment. Future trouble will probably come from the scarcity of these "added ingredients" - It is no good having the ability to increase the manufacture of 'stainless' magnesium if it costs too much to get the additives! Doesn't China have the lion's share of a lot of these rare metals?

The Skud
29th August, 2013 @ 07:21 pm PDT

Arsenic has been used to treat wood for decades. Most, if not all exterior wood structures are made with arsenic-treated wood.

Christian Lainesse
30th August, 2013 @ 04:59 am PDT

Bah, enough talk of arsenic please. Exercise proper fabrication and end of life methodologies and all will be happy.

Just imagine the weight savings, better handling, improved fuel efficiency, longer tire lifetime of your car to name some with an engine block or chassis made out of magnesium. I'd buy it.

Fretting Freddy the Ferret pressing the Fret
30th August, 2013 @ 06:35 am PDT

@ Christian Lainesse

It is why I don't use treated wood.

Slowburn
30th August, 2013 @ 02:33 pm PDT

'Piston Engine" fossil fuel age is at its end, but many, even better uses for this "alloy" come to mind!

Bruce Miller
2nd September, 2013 @ 05:57 pm PDT

Donzie, I agree with you but you forgot to tell people about the toxicity of beryllium, my guess is that most people here are not aware of that fact.

We have a society of people who seem to scared of just about every thing especially things they know little about.

To the Skud, none of the elements listed are rare earth metals and even most of the rare earth metals are not that rare it is just that China produced them so cheaply that everyone else gave up because of the lack of profits. Just one of the many ways governments including the US can screw up the price of commodities.

katgod
2nd September, 2013 @ 06:32 pm PDT

@ Bruce Miller

Not unless batteries get a lot better, or governments take ill advised actions.

Slowburn
3rd September, 2013 @ 01:32 am PDT

Shouldn't they be concentrating on applications for graphene, practical production and utilisation.

Sadaf Dawar
3rd September, 2013 @ 04:33 pm PDT

@ Sadaf Dawar

The fundamental problem with graphene is the exorbitant cost of producing it. There are already plenty of uses lined up for when the price comes down to mere stratospheric levels.

Slowburn
5th September, 2013 @ 01:32 am PDT

Concerning the ill-informed comments expressing fear of catastrophic conflagration, it is worth pointing out that magnesium has been widely used in the automotive industry for decades, the most common use being VW Beetle crankcases, and as far as I know, there has never been a single recorded case of a Beetle engine spontaneously combusting.

Many racing car and motorcycle castings are magnesium, and it has been in common use in aviation since WWII.

However, corrosion has always been a problem, if this really has been eliminated or even substantially reduced, this will be a great advantage.

However, this susceptibility to corrosion has an up side, a great deal of magnesium is used for sacrificial anodes on marine equipment from outboard motors to oil rigs, you can practically watch an iron ship dissolving if its anode falls off!

Catweazle
12th September, 2013 @ 06:30 am PDT
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