Under the microscope
The article on Advanced Metals last month briefly touched on some materials which have been tried and tested in Formula One with varying degrees of success, and in this article we shall look a little deeper at some of the materials currently being used or under investigation, and examine how these differ from the more traditional grades used.
Whilst Formula One is frozen at present in terms of introduction of new materials owing to the homologation
of the engines, we should not fool ourselves into thinking that the materials departments of these organisations are asleep or redundant. There is much to be gained from being prepared for any new regulation change, and the Formula One engine manufacturers will be very busy testing and evaluating improved materials.
The general trend is always for an increase in a certain mechanical or physical property of the material, and with the increased number of races that a Formula One engine must now run before being replaced without penalty, increased fatigue resistance is probably now more important than ever.
For structural castings over the years, we have seen the foundries pushed to move from the old LM alloys such as LM25 (a 7% silicon alloy which has an aerospace equivalent called L99, also equivalent to A356) to higher strength alloys such as L169 (equivalent to A357), which is distinguished by its higher magnesium content. Other A35x specification alloys have also found widespread use in Formula One and some other formulae, owing to better fatigue resistance, but there is a concerted push by some to move to more exotic aluminium casting alloys which promise outstanding fatigue behaviour. These exotic alloys have particular difficulties in producing the quality of castings required but, once casting development is completed, they promise large gains, so we can expect their use to become widespread as time goes on, especially under new engine regulations.
There have been many attempts to improve upon the traditional piston alloys over the years, but still many keep returning to the old favourite RR58 / 2618A or something only slightly modified from this specification. RR58, containing 1.9 – 2.7% of copper, has a good combination of properties that have seen it used from World War II (it was developed for the Rolls-Royce Merlin engine) until the current Formula One era. Not only does it have good hot-strength, but it maintains excellent fatigue behaviour and ductility making it resistant to minor damage from debris and even unexpected collisions with valves. I have seen a piston with a failed valve-head embedded in it without causing a catastrophic piston failure. The high-silicon 4032 alloy has also been used for Formula One pistons in recent years. However, these traditional materials should not expect that their place at the top table is guaranteed for much longer. Manufacturers have for many years looked to find something with better properties and now some feel that they are close to finding something considerably better. I have seen results of trials of pistons run in Formula One engines which look very promising. The alloy in question has excellent strength and exceptional fatigue resistance, but lacks slightly in ductility meaning that it has very little tolerance to minor damage, but also any contacts have to be very carefully designed indeed. Whilst this material is probably a little too risky to be introduced at present, work is ongoing to find something with a little more elongation.
I have been in contact with an engine materials expert recently who has access to a new piston alloy which is claimed to be a big step forward from the traditional alloys. We can certainly expect to see this undergoing trials in the near future with a view to introducing this under new Formula One engine regulations. Those who are unrestricted in this way (MotoGP and other formulae such as ALMS) might do well to avail themselves of this material. With much increased fatigue resistance, it may well be that rarest of commodities – a money-saver!
Written by Wayne Ward.