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.

The foundry workers would probably get sick.

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.

"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.

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

@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.).

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.

Promising discovery ...

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?

@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.