18 replies to this topic

[desmo]

I found this on Ford Racing's website:

"The next year[1994], Benetton received the latest engine creation from Ford and Cosworth, the Zetec R V8. This one incorporated all the latest technology, including the application of ceramics to the cylinder head, hollow titanium valves, titanium connecting rods and magnesium alloy pistons."

Now I know back in pre WWII days Mg alloy pistons were pretty normal stuff in racing engines, but is anyone aware of any other instances of Mg pistons in more modern F1 applications? And why is the material so feared by most engineers for structural applications other than wheels? Mario Ilien in his recent Racetech interview basically said he wanted nothing to do wih Mg.

[FordFan]

I know that Mg is pretty flammable (thinking back to high school chemistry experiements). With thousands of explosions going on per minute, might scare someone away. I would have thought it would be straight forward to make a safe alloy, though.

[blkirk]

In large pieces, Mg isn't really any more flammable than other metals. The trouble comes in machining the stuff. Magnesium cuttings are considered hazardous waste because they are so easy to ignite and very hard to extinguish. There was a group doing a magnesium design contest back when I was at school. They had over 100 small fires break out while they were machining their parts. When they finished they took the bucket of cuttings out into a field and set it on fire because no waste disposal company would touch it with a 10' pole.

As far as structural applications go, Mg has no fatigue limit. This means that every Mg part will eventually fail through fatigue. To make matters worse, machined or polished Mg has a lower fatigue life than cast, forged, coated, or bead-blasted Mg. So, if the part needs a good surface finish (such as any internal engine part) Mg will not have a good fatigue life.

Magnesium is also half as stiff as aluminum. With the high loads and tight tolerances of modern F1 engines (and chassis, too), I'd rather not have to worry about parts flexing and stretching.

[desmo]

Given the downsides of Mg alloys stated, it is strange to me that they are still universally used for wheels and commonly used for gearbox cases, which have significant suspension loads fed into them.

I also believe that similar flammibility (non)issues exist with Ti as well, so I don't think this is a major factor in Mg's limited application in F1.

[blkirk]

Both wheels and gearboxes can be cast or forged with only a minimum of machining required on the final part. Cast parts last longer, and with only a small amount of machining to do, there's less risk from small shavings catching fire. Also, with it's low density (about 2/3 that of aluminum), it can do wonders for unsprung mass and polar moment of inertia.

I think this is why the teams persist in using magnesium in the wheels and gearboxes. The downsides are fairly well minimized and it can reduce mass in two of the most critical areas of the car.

PS. Desmo, your sig is rather appropriate for this thread.;)

[Halfwitt]

A few years ago I had a leaflet somewhere from a magnesium company in the UK , and it shows a V10 engine block and a motorcycle piston. I don't know if anyone ever used a magnesium piston or block in recent times, but vertainly the capability to manufacture these components exists even if nobody wants them.

[desmo]

I don't see machining or flammability issues as germane to why we don't see more use of Mg alloys for pistons or engine blocks. Fatigue life or elastic modulus or the basic conservatism of race engineers when it comes to new materials seem more likely reasons to me. Mg alloys have a pretty good track record in these applications actually. Questions of modulus or strength could potentially be addressed by the addition of reinforcements- Mg alloy matrix MMCs. BMW engineers have published research into this.

F1 has been very slow to adopt new or innovative materials (not that Mg really falls into either category) when it comes to engines.

[desmo]

On the apparent conservatism of F1 engineers when it comes to innovative materials I posted this in a mirror thread over on TNF on this topic. I posted over on that forum to tap the considerable knowledge base that exists over there and unfortunately little intellectual cross-pollination occurs between the fora.


John Judd from Racetech magazine 1998:

"I think that still universal in F1 are nitrided steel cranks, Ti two-bolt con rods, multi-phased bolts, RR58 [an alloy developed by Rolls-Royce for the WWII Merlin aero engine!] Al pistons and steel gudgeon pins retained by round wire circlips.

"People say that current performance is possible due to advances in materials but I don't think that is the case. If you look at what we couldn't have before the war, I don't suppose you could of had the PTFE seals for the airsprings, so the airsprings wouldn't have worked back then. Multi-phased bolts would not have been around.

"Ti? Maybe not but it was certainly around in the 60s. We had some Ti rods for the Coventry Climax engine in 1963. It is quite likely that that by 1963 the other things I mentioned were available."

I think that with the current ban on AlBeMet, those words are substantially still true today, although I don't think superior alpha/beta Ti alloys currently used such as 6Al/4V were available for non-military use then, the Ti rods of the 60s being CP (Commercially Pure) or similar spec.

I just find it astonishing that at least as of a couple of years ago, F1 engines, these paragons of high tech, were being assembled from materials that are substantially similar to those in use 30, 40 years or even longer ago!

[GrooveJet]

Desmo, exceuse my ignorance, but can you explain what "multi-phased bolts" are.

[desmo]

Multi-phase alloys are microscopically inhomogeneous with differing crystalline structures contained within them. They exhibit superior ductility and plasticity properties as well as excellent strength. Some exhibit transformation of the phases within the alloy in response to strain or deformation. Maraging steels which you might be familiar with as they are used in golf clubs are a multi-phase alloy. Those metal frames for glasses that will snap back after severe deformation are another multi-phase alloy. The con rod bolts and other fasteners used in an F1 engine are likely to be of this type of steel. There are actually people who invest on these steels as one would precious metals as a speculative investment. Seldom seen in common use they are most apt to be found in aerospace applications.

[Cory Padfield]

Desmo,

The reasons Mg is not used more extensively include:

low elastic moduli

low strength

high thermal expansion coefficient

low wear resistance

loss of elastic moduli and strength at elevated temperatures - this one is Mario Illien's main reason to avoid Mg.

ignorance of properties, alloys, etc.

lack of wrought alloy development - most Mg is used for die castings, which is great for high volume, low cost passenger vehicle applications, but not for low volume F1 uses.

Personally, I think all of these can be overcome. One need look no further than the success of wheels to show how high strength, low mass components can be made.

Cory

[desmo]

Obviously the people at Cosworth agreed with you when the chose Magnesium Nickel Copper alloy pistons for their 1994 F1 engine.

[Halfwitt]

Originally posted by desmo
Obviously the people at Cosworth agreed with you when the chose Magnesium Nickel Copper alloy pistons for their 1994 F1 engine.

Are we to assume from that comment that with hindsight that they now no longer agree and are using more conventional alloys? I don't think that Cosworth have in recent years (upto the advent of the initial CR-1 design) proiduced the best engines.

Listening to the arguments for why aluminium beryllium is used for pistons, it would seem that all of magesium's properties run counter to this, other than density of course. They offer low strength, low fatigue resistance, low thermal conductivity as so on. I can see its benefit for low temperature applications and ones where fatigue is less of an issue, but when somebody like Mario Illien avoids a material such as magnesium there has to be quite compelling reasons. Ilmor / Mercedes as a single entity have, if they see a significant benefit to using Mg, the expertise and the money to carry it off. The fact that they make no effort or very little means that they forsee no great advantage.

[david_martin]

Originally posted by Cory Padfield
Personally, I think all of these can be overcome. One need look no further than the success of wheels to show how high strength, low mass components can be made.

Cory

Well all of them except perhaps the low elastic modulus and high thermal expansion coefficient, both of which are the biggest problems in reciprocating engine internals like pistons and conrods. The obvious way to solve this is to go to a Mg based MMC, but going down this route it not particularly easy either. Powder metallurgy with Mg is really not a viable option, and the castability and wetability of Mg melts makes pressure casting the parent Mg around a fibre pre-form pretty difficult too. Mg Alloys are notorious for extremely poor room temperature ductility, which makes precision machining and surface polishing, even in near-net shaped parts, rather difficult. Cold forging and other room temperature forming processes are basically impossible.

I think Mg alloys offer a lot more promise in "bulk" applications, where larger cast sections can be used - stuff like casings, bulkheads, wheels, space frame locators. We will see a large ramp up in Mg Alloy applications for road cars over the next few years, but in racing engines I believe there are superior alternatives.

[desmo]

The fact that they were used successfully as recently as that in a top-line F1 engine suggests to me that they are not intrinsically unsuitable for the application. The fact that they are apparently no longer used suggests that the upside was apparently deemed insufficient to justify further development effort at the time.

Given that Goto once stated that each gram taken off per piston is potentially worth 10bhp in top end and that alloys developed prior to WWII are still in widespread use in F1, I can only conclude that materials technology for pistons is astonishingly stagnant. I am told that MMCs are the next logical step and that Mg alloy matrix MMCs address many of the downsides of straight Mg alloy pistons, although the focus of development appears to be Al/ceramic composites. Al alloys presently used have pretty dismal high temp properties too, and cooling oil jet sprays are necessary to keep them from failure in F1 engines. Another possibility with considerable potential is carbon/carbon, but carbon and aramid reinforced materials are excluded by the tech regs.

[david_martin]

Originally posted by desmo
The fact that they were used successfully as recently as that in a top-line F1 engine suggests to me that they are not intrinsically unsuitable for the application. The fact that they are apparently no longer used suggests that the upside was apparently deemed insufficient to justify further development effort at the time.

That is certainly one interpretation, and one I would mostly agree with. I do, however, suspect a rather important fact has been overlooked in this discussion. That Cosworth Zetec R engine was a 3.5 litre V8, with a redline which is probably about 3.5k rpm lower than the current 3.0 litre Cosworth V10. I would expect piston thermal and mechanical duty cycles in the two engines to be rather different - and the current V10 would be a lot more severe. I think it is not an accident that the increase in F1 engine speeds and the use of high specific stiffness, low thermal expansion materials like Be alloys and Al MMC's are coincident......;)

[desmo]

If we are still on the subject of piston materials how does that square with Ilien's comment in his recent Racetech interview that Ilmor was still recently using RR58 "Merlin" alloy for pistons? Or was he just misleading us on that score? Or is RR58 still a near state of the art material?

Are steel pistons out of the question? Some of the "rocket motor" maraging alloys have pretty astounding physical properties.

So many questions!

[david_martin]

Originally posted by desmo
If we are still on the subject of piston materials how does that square with Ilien's comment in his recent Racetech interview that Ilmor was still recently using RR58 "Merlin" alloy for pistons? Or was he just misleading us on that score? Or is RR58 still a near state of the art material?

Are steel pistons out of the question? Some of the "rocket motor" maraging alloys have pretty astounding physical properties.

So many questions!

Nope I reckon Mario is telling the truth.

RR58 "Hiduminium" or 2618 to give it its modern name, it still very much with us and widely used in elevated temperature structural applications - it is one of the classic aerospace Al alloys. It is an Al-Cu alloy (nominally Al-2.3Cu-1.6Mg-1.1Ni-0.18-0.07Ti) which exhibits an excellent percipitation hardening response (T61 temper is pretty normal) giving high yield strengths, is very easy to forge, has good machining properties and excellent (by Al standards anyway) stability of properties at elevated temperatures. Which is why it is an ideal piston material, although it is used for lots of other things too - Concorde is made almost entirely from it. It is also becoming a popular parent alloy for using in Al MMC's, especially SiC particle reinforced ones for aerospace structures - I would not be suprised if some of the MMC's in F1 engines are 2618 based

Steel pistons is an issue for another day

[david_martin]

Originally posted by desmo
Are steel pistons out of the question? Some of the "rocket motor" maraging alloys have pretty astounding physical properties.

Steel probably is out of the question, but not necessarily for the reasons you might imagine. While the specific stiffness of ferrous alloys is inferior to what could be achieved with light metals or light metal composites, the kind of yield strengths achievable do make for some very impressive specific strength values.

The biggest problem with ferrous alloys in an application like pistons is manufacturing them. To exploit the high specific strength would require extremely thin sections which are going to be very hard to make. Pressure die casting and powder metallurgy are really great ways to make complex 3D shapes from low melting temperature materials, but neither are really ideal for iron - it has a liquidus temperature of over 1375 degrees Celcius. Near net shaped forging and machining are the best route for processing ferrous alloys, but getting down to kinds of sections necessary to achieve the low mass is going to be really tough. Iron also has the complicating factor of the FCC to BCC transformation - maintaining geometrical integrity after hot working and heat treatment can be really very difficult. So I suspect that ferrous alloys are probably a less attractive proposition for pistons than the light metals.