Application Status Of Titanium Alloys in The Automobile Industry
In recent years, with the rapid development of the automobile industry, the fuel consumption, environmental protection and safety issues generated by automobiles have attracted increasing attention. Looking forward to the future development direction of the automobile industry, lightweight, low fuel consumption and low emissions are the themes of development. According to statistics from international authoritative departments, 60% of the energy of automobile fuel combustion is consumed by its own weight. Although high-strength thin steel plates, aluminum, magnesium, metal-based composite materials and plastic resin materials have played a role in reducing the weight of automobiles, the emergence of industrial titanium materials has made automobile manufacturing a better choice.
Titanium metal has the advantages of low density, high specific strength and good corrosion resistance. The use of titanium materials in automobiles can greatly reduce the weight of the car body, reduce fuel consumption, improve the working efficiency of the engine, improve the environment and reduce noise. However, the expensive price makes titanium alloys only have some applications in luxury models and sports cars in the automobile industry, and rarely in ordinary cars. Therefore, research and development of low-cost titanium alloys that meet market needs is the key to promoting its application in ordinary household cars.
Current application status of titanium alloys in the automobile industry
Although titanium alloys have been widely used in aerospace, petrochemical and shipbuilding industries, their application in the automobile industry has developed slowly. Since the first all-titanium car was successfully developed by General Motors in the United States in 1956, titanium auto parts did not reach the level of mass production until the 1980s. In the 1990s, with the increasing demand for luxury cars, sports cars and racing cars, titanium parts have developed rapidly. In 1990, the amount of titanium used in automobiles worldwide was only 50 tons, which reached 500 tons in 1997, 1100 tons in 2002, and 3000 tons in 2009. It is expected that the amount of titanium used in automobiles worldwide will exceed 5000 tons in 2015. At present, the following titanium alloy parts are commonly used.
1. Engine connecting rod
Titanium alloy is an ideal choice for connecting rod materials. Engine connecting rods made of titanium alloy can effectively reduce engine weight, improve fuel efficiency and reduce exhaust volume. Compared with steel connecting rods, titanium connecting rods can reduce 15% to 20% of the weight. The application of titanium alloy connecting rods was first reflected in the new Ferrari 3.5LV8 and Acura NSX engines in Italy. The materials used for titanium alloy connecting rods are mainly Ti-6Al-4V, Ti-10V-2Fe-3Al, Ti-3Al-2.0V and Ti-4Al-4Mo-Sn-0.5Si, and other titanium alloy materials such as Ti-4Al-2Si-4Mn and Ti-7M-4Mo are also being developed for use in connecting rods.
2. Engine valves
Automobile engine valves made of titanium alloys can not only reduce weight and extend service life, but also reduce fuel consumption and improve automobile reliability. Compared with steel valves, titanium valves can reduce weight by 30% to 40%, and the engine limit speed can be increased by 20%. As far as current applications are concerned, the material of the intake valve is mainly Ti-6Al-4V, and the material of the exhaust valve is mainly Ti-6242S. Usually Sn and Al are added together to obtain lower brittleness and higher strength; the addition of Mo can improve the heat treatment performance of titanium alloys, enhance the strength of quenching and aging titanium alloys, and increase hardness. Other titanium alloys with development potential are:
1) The intake valve can be made of Ti-62S, which has the same characteristics as Ti-6Al-4V and is cheaper.
2) The exhaust valve can be made of Ti-6Al-2Sn-4.0Zr-0.4-Mo-0.45Si. Due to its lower Mo content, its creep resistance is better than that of Ti-6242S, and its oxidation resistance temperature can reach 600°C.
3) The exhaust valve can be made of γ-TiAl, which has the characteristics of high temperature resistance and light weight, but is not suitable for processing by traditional forging methods, and is only suitable for casting and powder metallurgy.
3. Valve spring seat
High strength and fatigue resistance are the properties that valve spring seats must have. β titanium alloy is a heat-treatable alloy that can obtain high strength through solid solution aging treatment. The corresponding more suitable materials are Ti-15V-3Cr-3Al-3Sn and Ti-15Mo-3Al-2.7Nb-0.2Si. Mitsubishi Motors uses Ti-22V-4Al titanium alloy valve spring seats on its mass-produced cars, which reduces the mass by 42% compared to the original steel lock, reduces the inertial mass of the valve mechanism by 6%, and increases the maximum engine speed by 300r/min.
4. Titanium alloy springs
Titanium and its alloys have a lower elastic modulus than steel materials, a large σs/E value, and are suitable for manufacturing elastic components. Compared with steel automobile springs, under the premise of the same elastic work, the height of titanium springs is only 40% of that of steel springs, and the mass is only 30% to 40% of that of steel springs, which is convenient for body design. In addition, the excellent fatigue performance and corrosion resistance of titanium alloys can increase the service life of springs. At present, titanium alloy materials that can be used to manufacture automobile springs include Ti-4.5Fe6.8Mo-1.5Al and Ti-13V11C-3Al.
5. Turbocharger
Turbochargers can improve the combustion efficiency of engines and enhance the power and torque of engines. The turbine rotor of the turbocharger needs to work in high-temperature exhaust gas above 850℃ for a long time, so it is required to have good heat resistance. Traditional light metals such as aluminum alloy cannot be used due to their low melting point. Although ceramic materials are used in turbine rotors because of their light weight and good high-temperature resistance, their application is limited due to high cost and the inability to optimize the shape. In order to solve these problems, Tetsui et al. developed the TiAl turbine rotor. After many tests and verifications, it not only has good durability and efficiency, but also can improve the acceleration of the engine. This design has been successfully commercialized in the Mitsubishi Lancer Evolution series.
6. Exhaust system and muffler
Titanium is used in large quantities in the exhaust system of automobiles. Exhaust systems made of titanium and its alloys can not only improve reliability, extend life and improve appearance, but also reduce mass and improve fuel combustion efficiency. Compared with steel exhaust systems, titanium exhaust systems can reduce mass by about 40%. In the Golf series of cars, the weight of the titanium exhaust system can be reduced by 7 to 9 kg. Currently, the titanium used in the exhaust system is mainly industrial pure titanium.
The weight of the titanium muffler is only 5 to 6 kg, which is lighter than stainless steel mufflers. The 2000 Chevrolet Corvette Z06 uses an 11.8 kg titanium muffler and tailpipe system to replace the original 20 kg stainless steel system, reducing the weight by 41%. The strength of the replaced system remains unchanged, and the car is faster, more flexible and fuel-efficient. The titanium used in the muffler is also mainly industrial pure titanium.
7. Body frame
In order to improve the safety and reliability of the car, it is necessary to consider the design and manufacturing aspects, especially the manufacturing materials. Titanium is a good material for making body frames. It not only has a high specific strength, but also has good toughness. In Japan, car manufacturers choose pure titanium metal welded pipes to make body frames, which can make drivers feel safe enough when driving.
8. Other titanium alloy parts
In addition to the above parts, titanium is also used in engine rocker arms, suspension springs, engine piston pins, automotive fasteners, lug nuts, automotive door protrusion beams, automotive stop brackets, brake caliper pistons, pin bolts, pressure plates, shift buttons and automotive clutch discs and other automotive parts. The new generation of automotive designs pays more attention to the lightweight body, low fuel consumption, low noise and light vibration of the engine to meet the increasingly stringent environmental requirements. In this context, light metal titanium will become a major application material for future automobiles.
