Forged Titanium Alloys for Automotive Crankshafts

Forged Titanium Alloys for Automotive Crankshafts

When a race car engine reaches its peak performance, the rods that support the pistons are subjected to enormous forces.forged titanium alloy automobile crankshaft These forces are generated by the reciprocating motion of the crankshaft, resulting in bending and torsional stresses. Consequently, the selection of connecting rod material is a critical decision. While steel is a solid choice, titanium can provide unmatched responsiveness and acceleration.

For the enthusiast seeking to maximize power output, forged titanium is an excellent option.forged titanium alloy automobile crankshaft Titanium is 30% lighter than its steel counterpart, reducing the weight of the crankshaft by nearly a third. This can significantly increase the power of a racing engine without compromising durability or strength.

Titanium is also very difficult to machine, requiring specialized machining tools and procedures.forged titanium alloy automobile crankshaft In addition, it is very expensive, often four to five times the cost of a set of steel racing rods. For these reasons, titanium rods are typically reserved for high-performance cars that are capable of generating extreme amounts of horsepower and torque.

The most popular titanium alloy used in automotive connecting rods is Ti-6Al-4V, also known as ATI T-5. This titanium-aluminum-vanadium (Al-V) alloy has good mechanical properties at elevated temperatures and good corrosion resistance. It is heat treatable to achieve very high levels of tensile and fatigue strength. Additionally, it has good ductility at high strengths.

However, the A-V-Ti alloy cannot be used in engines that require a high level of torsional stiffness. The torsional stiffness of a rod journal increases with the square of its length and its diameter. Therefore, in order to obtain a high-strength, high-torsional-stiffness titanium alloy, it is necessary to make the rods shorter and larger in diameter.

For this reason, a titanium MMC alloy is being explored for use in high-performance rods. It is made from powder processed titanium containing 12% wt TiC, and it has very high strength, toughness, and modulus, as well as excellent wear resistance. Unlike traditional forged titanium, it has good machinability and weldability, even at high temperatures.

In particular, one manufacturer has developed a process that allows it to produce a deep case nitride layer in its A-V-Ti alloy, with a hardness of over 60 HRc at the surface and 40 to 45 HRc in the core. The depth of this case nitride layer is said to reduce the sharp hardness gradient, which in turn enhances fatigue resistance.

Although the development of titanium connecting rods is a promising step forward, it is unlikely to become mainstream in automobiles. Currently, titanium and its all-metal matrix composites are banned under the FIA's Formula One rules for the manufacture of crankshafts, so a titanium MMC crankshaft is not likely to be seen in top-level motorsport racing. However, the fact that a prototype has been run successfully with such a crankshaft suggests that the technology may eventually be brought to commercial production.

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