It has taken about two to three years of trial and error, but one American manufacturer believes they have found a new family of aluminium metal matrix materials for use in piston manufacturing. Rather than the customary silicon carbide matrix, a material that has a tendency to wear out manufacturing tools and has extremely sharp edges, this exclusive material consists of spheroidal aluminium oxide AI203 particles, randomly distributed as its reinforcement.
This allows the machining characteristics of the new materials to be considerably closer to that of non-reinforced aluminium alloys using conventional carbide tools, when compared to the machining difficulties encountered with silicon carbide reinforced aluminium alloys. The aluminium matrix alloy can either be taken from the current 2000, 6000 or 7000 series chemistries. (The exact aluminium alloy chemistry used from any one of these three series is proprietary.)
According to Del West program director, Len Gibbs, “The 2000 series chemistry materials will be suitable for use in piston manufacturing because it has a lower thermal expansion than convention aluminium piston alloys such as 2618 and 4032, by as much as 25 percent in the case of 2618.
“The lower thermal expansivity of the new material will permit better sealing at the piston: cylinder wall, thereby enhancing performance. The new alloy composition also has better stiffness and elevated temperature strength than 2618 and heat transfer similar to 4032,” he said.
“The lower thermal expansion of the new metal should lead to a benefit in piston ring life,” Gibbs mused. “More than anything else, I think the piston ring will gain longer life and a better seal, in particular because this material expands more slowly than the conventional aluminium alloys. The four important properties of this material are its better machinability, low rate of thermal expansion, its high tensile strength and its greater stiffness.”
There has been extensive testing on a 7000 series matrix alloy using Spintron to ensure validity of the material under the highly stressed condition associated with a valve spring retainer. “I’d say we’ve had about six million cycles on a retainer using a Michigan (International Speedway) NASCAR Sprint Cup track loading profile. What is interesting, Gibbs said, “is that retainers made of this material weigh about 20 percent less than titanium retainers.”
With the capability to blend its own alloys, the company can vary the amount of AI203 reinforcement volume in the process, according to Gibbs. “We can vary the percentage of reinforcement and work with the properties to increase strength and stiffness for use in piston manufacture,” he said.
Work continues with several partners to determine proper piston design using the new material, which is made on-site in Valencia, California. The material is applicable for racing series that permit metal matrix materials, and Gibbs can envision diesel applications for the products.
It has taken a long time to develop the alloy and modify the chemistry for use in piston manufacture, as well as to standardise the manufacturing process. “There are many requirements we have to meet for the manufacturing of this alloy.” When will it be available to customers? Gibbs is not ready to make any promises, but more information is expected in the coming months.
Written by Anne Proffit.