Magnesium cylinder heads
Magnesium cylinder heads
(OP)
What are the main problems with using magnesium for cylinder heads? It is much lighter than aluminum, and has a thermal expansion close to that of aluminum. Aprilia has made a cylinder head out of magnesium, but no one else seems to want to take advantage of the much lighter weight.





RE: Magnesium cylinder heads
FWIW I know that for one particular engine there is a minimum stiffness we want, and it is somewhere between that supplied by the minimum castable thickness of cast iron, and that of the minimum castable wall thickness of aluminium.
Having said that I can see that in certain cases magnesium would have advantages.
Cheers
Greg Locock
RE: Magnesium cylinder heads
I have seen carbon fibre reinforced aluminium castings - most notably pistons! I would imagine these are cast in the absence of oxygen, to avoid carbon burning up. Any kind of stiff fibre reinforced component (head or otherwise) strikes me as a more practical proposition.
Maybe I'm wrong - who knows...
Mart
RE: Magnesium cylinder heads
RE: Magnesium cylinder heads
As sreid suggests, creep is a problem with magnesium at elevated temperatures. In our testing of magnesium casting alloys from the 1970's the material begins to lose tensil strength at approximately 100 degrees C. At 120 degrees C creep is a serious factor. Screw threads are at risk and can fail at 120 C. The compressibility of the alloy at elevated temperatures is dramatic. There goes the fastener per-load.
There is a new magnesium alloy (can't recall the vendor) that has much better elevated temperature properties. Supposedly anyway . . . I sure wouldn't use magnesium for a cylinder head until I saw some very convincing life cycle tests!
WH
RE: Magnesium cylinder heads