Why Magnesium isn't Used Much for Engine Castings

[wolram]

Why is magnesium not used much for engine castings? the old air cooled VW engines were light enough (bare) to be easily lifted by one person surely there is a big power to weigh ratio to be gained.
If i remember correctly added copper reduced corrosion to after market castings.

 

[brewnog]

Cost, generally. A few of the German OEMs have started playing with it again recently, I think the new BMW I6 engines have a magnesium alloy block (albeit with an aluminium alloy cylinder liner).

 

[Savant13]

Magnesium is flammable. I'm not sure if engine temperatures would be high enough for ignition, but it is definitely something to consider.

 

[LURCH]

A friend of mine had his engine catch fire in a parking lot. No way you can extinguish them once they get started. Also no way Gary is ever buying another engine with a magnesium block.

 

[Proton Soup]

magnesium is a common "firestarter". you shave a bit of Mg off a block, strike a spark to it, and voila, you've got fire.
https://www.amazon.com/dp/B0002X1IOM/?tag=pfamazon01-20

 

[mgb_phys]

Magnesium is flammable but so is aluminium (ever heard of thermite?) Mg is 30% lighter than Al and 75% ligther than steel.
You can put out a Mg fire - you just need the right sort of extinguisher (the same dry powder you need for Al), however if a fire is hot enough to burn an engine block you are generally better off just standing back and watching from a safe distance.
Its generally failry safe in big blocks - it's very scary to machine though!
I visited a contractor machining Mg gearboxes for Apache helicopters, you have to high speed machine parts without letting any chips touch air!
You use a lot of coolant and they are very careul about sweeping the swarf.

Generally it isn't used much becase the weight of cars hasn't mattered much, there's no point in saving 50Kg off the weight of the engine block if you put it in a 3000kg SUV.

 

[Topher925]

Isn't Magnesium also not very malleable? Wouldn't it give some issues with temperature gradients and cracking under high stress operation?

 

[mgb_phys]

If you have the right alloy it can be worked pretty much the same as Aluminium.
Not sure I would want to weld it though ;-)

 

[mender]

Welding magnesium just requires ensuring that a shielding gas surrounds the piece being welded with a short period of gas flow after the weld is completed.

 

[mgb_phys]

Welding magnesium just requires ensuring that a shielding gas surrounds the piece being welded with a short period of gas flow after the weld is completed.

In general yes - the danger is that sparks from an arc welding robot landing on the car.

http://wwwdelivery.superstock.com/WI/223/2139/PreviewComp/SuperStock_2139-559043.jpg