Titanium Alloy Leads Automotive Technology

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 body mass, reduce fuel consumption, improve engine efficiency, improve the environment and reduce noise. However, the high price makes titanium alloys only have some applications in luxury models and sports cars in the automobile industry, and rarely used in ordinary cars. Therefore, research and development of low-cost titanium alloys that meet market needs is the key to promoting their application in ordinary household cars.

Although titanium alloys have been widely used in aerospace, petrochemical and shipbuilding industries, their application in the automotive industry has developed slowly. Starting from the successful development of the first all-titanium car 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, as the demand for luxury cars, sports cars, and racing cars increased year by year, titanium auto parts Manufactured parts have developed rapidly. In 1990, the amount of titanium used in automobiles around the world was only 50t. In 1997, it reached 500t. In 2002, it reached 1,100t. In 2009, it reached 3,000t. It is expected that the amount of titanium used in automobiles around the world will exceed 5,000t in 2015. At present, the following types of titanium alloy parts are commonly used.

1. Engine connecting rod
Titanium alloy is an ideal material for connecting rods. Engine connecting rods made of titanium alloy can effectively reduce engine mass, improve fuel efficiency and reduce exhaust volume. Compared with steel connecting rods, titanium connecting rods can reduce the mass by 15% to 20%. The application of titanium alloy connecting rods was first reflected in Italy's new Ferrari sedan 3.5LV8 and Acura's NSX engine. The main materials used in titanium alloy connecting rods are Ti-6Al-4V, Ti-10V-2Fe-3Al, Ti-3Al-2.0V and Ti-4Al-4Mo-Sn-0.5Si. Other titanium alloy materials such as Ti-4Al The application of -2Si-4Mn and Ti-7M-4Mo in connecting rods is also under development.
2. Engine valve
Automotive engine valves made of titanium alloy can not only reduce mass and extend service life, but also reduce fuel consumption and improve vehicle reliability. Compared with steel valves, titanium valves can reduce mass by 30% to 40%, and the engine's 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 properties of titanium alloys, enhance the strength of quenching and aging titanium alloys, and increase the hardness. Other titanium alloys with development potential include:
1) The intake valve can be made of Ti-62S, which has properties equivalent to Ti-6Al-4V and is cheaper.
2) The exhaust valve can be made of Ti-6Al-2Sn-4.0Zr-0.4-Mo-0.45Si. Because of its lower Mo content, its creep resistance is better than Ti-6242S, and its oxidation resistance 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 it is not suitable for traditional forging methods during processing. It is only suitable for casting and powder metallurgy processing.
3. Valve spring seat
High strength and fatigue resistance are must-have properties for the valve spring seat. Beta titanium alloy is a heat-treated 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 in its large-scale production vehicles, which reduces the mass by 42% compared with the original steel locks, reduces the inertial mass of the valve mechanism by 6%, and increases the maximum engine speed. 300r/min.
4.Titanium alloy spring
Titanium and its alloys have lower elastic modulus and larger σs/E value than steel materials, making them 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 steel springs, and the mass is only 30% to 40% of steel springs, which facilitates car body design. In addition, the excellent fatigue properties and corrosion resistance of titanium alloy can extend the service life of the spring. Currently, titanium alloy materials that can be used to make automobile springs include Ti-4.5Fe6.8Mo-1.5Al and Ti-13V11C-3Al.
5. Turbocharger
Turbochargers can improve engine combustion efficiency and enhance engine power and torque. The turbine rotor of the turbocharger needs to work in high-temperature exhaust gas above 850°C for a long time, so it requires good heat resistance. Traditional light metals such as aluminum alloys cannot be used due to their low melting points. Although ceramic materials are used in turbine rotors due to their light weight and good high temperature resistance, their application is limited due to their high cost and inability to optimize their shape. In order to solve these problems, Tetsui and others developed the TiAl turbine rotor. After many tests, it has been verified that it not only has good durability and efficiency, but also can improve the acceleration of the engine. This design has been successfully commercialized on the Mitsubishi Lancer Evolution series.
6. Exhaust system and muffler
Titanium is used extensively in automobile exhaust systems. 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 approximately 40%. In Golf series cars, the mass of the titanium exhaust system can be reduced by 7 to 9 kg. Currently, the titanium material used in the exhaust system is mainly industrial pure titanium.
The titanium muffler weighs only 5 to 6 kg, which is lighter than stainless steel and other mufflers. The 2000 Chevrolet Corvette Z06 uses an 11.8kg titanium muffler and exhaust pipe system instead of the original 20kg stainless steel system, reducing the mass by 41%. The replaced system maintains its strength and makes the car faster, more flexible and more fuel efficient. The titanium material used in the muffler is also mainly industrial pure titanium.
7. Body frame part
In order to improve the safety and reliability of automobiles, it is necessary to consider the design and manufacturing aspects, especially the manufacturing materials. Titanium is a very good material used to make car body frames. It not only has high specific strength, but also has good toughness. In Japan, automobile manufacturers choose pure titanium welded pipes to make body frames. This kind of frame can make drivers feel safe when driving.
8. Other titanium alloy parts
In addition to the above components, titanium is also used in engine rocker arms, suspension springs, engine piston pins, automotive fasteners, lug nuts, automotive door protruding beams, automotive gear brackets, brake caliper pistons, pin bolts, pressure Auto parts such as plates, shift buttons and automobile clutch discs.

1.Advantages

Titanium alloys have the advantages of light weight, high specific strength, and good corrosion resistance, so they are widely used in the automobile industry. The most common use of titanium alloys is in automobile engine systems. There are many benefits to using titanium alloys to manufacture engine parts, mainly reflected in:
1) The low density of titanium alloy can reduce the inertial mass of moving parts. At the same time, titanium valve springs can increase free vibration, weaken the vibration of the body, and increase the engine speed and output power.
2) Reduce the inertial mass of moving parts, thereby reducing friction and improving engine fuel efficiency.
3) Choosing titanium alloy can reduce the load stress of related parts and reduce the size of parts, thereby reducing the weight of the engine and the entire vehicle.
4) The reduction of the inertial mass of components reduces vibration and noise and improves engine performance.
The application of titanium alloys in other components can improve personnel comfort and the aesthetics of cars. In applications in the automotive industry, titanium alloys have played an immeasurable role in energy saving and consumption reduction.
2. Application restrictions
Although titanium alloy parts have such superior properties, there is still a long way to go before titanium and its alloys are widely used in the automotive industry. The reasons include high price, poor formability and poor welding performance.
With the development of titanium alloy near net shape technology and modern welding technologies such as electron beam welding, plasma arc welding, and laser welding in recent years, the forming and welding problems of titanium alloys are no longer the key factors restricting the application of titanium alloys. The main reason why it is widely used in the automotive industry is the high cost.
Whether it is the initial smelting of the metal or subsequent processing, the price of titanium alloys is much higher than that of other metals. The cost of titanium parts that the automobile industry can accept is 8 to 13 US dollars/kg for connecting rods, 13 to 20 US dollars for valves, and 8 for springs, engine exhaust systems, and fasteners. Below USD/kg. The current cost of parts produced with titanium materials is much higher than these prices. The production cost of titanium plates is mostly higher than 33 US dollars/kg, which is 6 to 15 times that of aluminum plates and 45 to 83 times that of steel plates.
Research status of titanium alloys for automobiles

picture
Currently, cost reduction is the main research direction of titanium alloys used in the automotive industry. In view of the characteristics of the cost distribution of titanium alloys used in the automotive industry, material research and development workers mainly achieve the purpose of reducing costs from the following two aspects: developing new low-cost alloy systems and using new processing and preparation technologies.

1. New low-cost titanium alloy system
Workers from various countries are developing new low-cost titanium alloy systems, mainly focusing on the following aspects: alloy design using cheap alloy elements and alloy design to improve processing characteristics. Among them, Japan and the United States are represented. my country has also successfully developed two low-cost titanium alloys, namely Ti8LC and Ti12LC. In the design of low-cost titanium alloy components for vehicles, commonly used cheap alloy elements include Fe, Cr, Si, Al, etc.
2. New processing and preparation technology
The processing cost of titanium alloy materials accounts for more than 60% of the total cost during the production process. Therefore, in terms of cost reduction, how to reduce the processing cost of titanium alloy has become a key research direction. Research in this area is mainly divided into two aspects: one is to improve the traditional casting and forging process, and the other is to adopt powder metallurgy near-net shape technology.
In the development of new forging processes, cold forging is currently one of the most promising methods for manufacturing automotive parts from titanium alloys. Beta titanium alloy has low deformation resistance at room temperature and is good in cutting and forming. It is a material that can be cold forged. Currently, Japan has developed three cold-deformed beta titanium alloys. Beta titanium alloy also has some shortcomings. It is prone to uneven deformation during cold forging and is easy to adhere to the mold. Therefore, mass production of beta titanium alloy parts using cold forging technology requires further exploration and development.
Powder metallurgy is a very important technology in reducing titanium alloy processing costs. In the manufacturing of powder metallurgy automotive parts, the traditional pressing-sintering method is still dominant, mainly including elemental powder method (BE) and pre-alloyed powder method (PA). At present, the elemental powder method is the most widely used in the field of low-cost automotive titanium alloy powder metallurgy due to its simple process and lower cost. In recent years, other powder metallurgy technologies have also emerged, including laser forming technology, metal powder injection molding (MIM) and other technologies. They have been widely used in the trial production and production of complex automotive parts, which can greatly shorten product development. and production cycle, further reducing costs.
Conclusion
The new generation of automobile design pays more attention to the lightweight body, low fuel consumption, low noise and light vibration of the engine to meet the increasingly demanding requirements of the environment. In this context, the light metal titanium will become a major application material for future automobiles.
Comprehensive consideration of the current research status of low-cost titanium alloys for vehicles can be found that in order to further reduce the cost of titanium alloys for vehicles, research should mainly focus on the following aspects:
1) In terms of the development of low-cost alloy systems, try to develop alloy systems that use no or less expensive alloy elements without affecting performance, and at the same time make full use of recycled titanium alloys.
2) In terms of casting and forging process development, develop in the direction of developing beta titanium alloys and cold deformed titanium alloys, and conduct feasibility studies on their mass production.
3) In terms of powder metallurgy, while ensuring the low-cost advantage, it is also necessary to further improve the performance of titanium parts.
With the development of the economy and the reduction of the cost of titanium, more engineering designers will choose titanium parts as automotive parts. Titanium alloys will eventually play an important role in automotive industry production.