In recent years, with the rapid development of the automotive industry, the issues of fuel consumption, environmental protection, and safety generated by automobiles have increasingly attracted people's attention. Looking ahead to the future development direction of the automotive industry, lightweight, low fuel consumption, and low emissions are the main themes of development. According to statistics from international authoritative departments, 60% of the combustion energy of automotive fuel is consumed by its own mass. Although high-strength steel sheets, aluminum, magnesium, metal matrix composites, and plastic resin materials have played a role in reducing the weight of automobiles, the emergence of industrial titanium materials has provided better choices for automotive manufacturing.
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 body weight, reduce fuel consumption, improve engine efficiency, improve the environment, and reduce noise. However, due to the high price, titanium alloys can only be used in luxury and sports cars in the automotive industry, and are rarely used in ordinary cars. Therefore, researching and developing low-cost titanium alloys that meet market needs is the key to promoting their application in ordinary household cars.
The current application status of titanium alloys in the automotive industry
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 1956, titanium automotive components 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 components developed rapidly. In 1990, the global titanium consumption in automobiles was only 50 tons. In 1997, it reached 500 tons, in 2002 it reached 1100 tons, and in 2009 it reached 3000 tons. It is expected that the global titanium consumption in automobiles will exceed 5000 tons by 2015. At present, there are several commonly used titanium alloy components.
1. Engine connecting rod
Titanium alloy is the ideal choice for connecting rod materials. Engine connecting rods made of titanium alloy can effectively reduce engine weight, improve fuel utilization, and reduce exhaust emissions. Compared to steel connecting rods, titanium connecting rods can reduce mass by 15% to 20%. The application of titanium alloy connecting rods was first demonstrated in Italy's new Ferrari sedan 3.5LV8 and Acura's NSX engine. The materials used in titanium alloy connecting rods mainly include 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-2Si-4Mn and Ti-7M-4Mo are also being developed for their applications in connecting rods.
2. Engine valves
The valve of a car engine made of titanium alloy can not only reduce weight and extend service life, but also reduce fuel consumption and improve the reliability of the car. Compared with steel valves, titanium valves can reduce mass by 30% to 40% and increase engine maximum speed by 20%. For current applications, Ti-6Al-4V is the main material for intake valves, and Ti-6242S is the main material for exhaust valves. Usually, Sn and Al are added together to achieve lower brittleness and higher strength; The addition of Mo can improve the heat treatment performance of titanium alloys, enhance the strength of quenched and aged titanium alloys, and increase hardness. Other titanium alloys with development potential include:
1) The intake valve can use Ti-62S, which has the same characteristics as Ti-6Al-4V and is relatively cheap.
2) The exhaust valve can use Ti-6Al-2Sn-4.0Zr-0.4-Mo-0.45Si. Due to its lower Mo content, its resistance to creep is better than Ti-6242S, and its oxidation temperature can reach 600 ℃.
3) The exhaust valve can be equipped with γ- TiAl has the characteristics of high temperature resistance and light weight, but it is not suitable to use traditional forging methods during processing. It is only suitable to use casting and powder metallurgy methods for processing.
3. Valve spring seat
High strength and fatigue resistance are essential properties for valve spring seats, β Titanium alloy is a heat treated alloy that can achieve high strength through solid solution aging treatment. The corresponding suitable materials include 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 vehicles, which reduces the mass by 42% compared to the original steel lock buckle, reduces the inertia mass of the valve mechanism by 6%, and increases the maximum engine speed by 300r/min.
4. Titanium alloy spring
Titanium and its alloys have a lower elastic modulus compared to steel materials, σ The s/E value is large, suitable for manufacturing elastic components. Compared with steel car springs, under the same elastic work, titanium springs have a height of only 40% of steel springs and a mass of only 30-40% of steel springs, which is convenient for vehicle design. In addition, the excellent fatigue performance and corrosion resistance of titanium alloy can improve the service life of springs. At present, titanium alloy materials that can be used to manufacture automotive springs include Ti-4.5Fe6.8Mo-1.5Al and Ti-13V11C-3Al.
5. Turbocharger
Turbochargers can improve the combustion efficiency of engines and enhance their power and torque. The turbine rotor of a turbocharger needs to work in high-temperature exhaust gases above 850 ℃ 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 point. Although ceramic materials are widely used in turbine rotors due to their lightweight and excellent high-temperature resistance, their high cost and inability to optimize their shape limit their application. To address these issues, Tetsui et al. developed TiAl turbine rotors, which have been verified through multiple tests to not only have good durability and efficiency, but also improve engine acceleration. This design has been successfully commercialized in the Mitsubishi Lancer Evolution series of vehicles.
6. Exhaust system and muffler
Titanium is widely used in the exhaust system of automobiles. The exhaust system made of titanium and its alloys can not only improve reliability, prolong life, and improve appearance, but also reduce mass and improve fuel combustion efficiency. Compared to steel exhaust systems, titanium exhaust systems can reduce mass by about 40%. In the Golf series of cars, the mass of the titanium exhaust system can be reduced by 7-9kg. Currently, the titanium material used in the exhaust system is mainly industrial pure titanium.
The mass of titanium silencers is only 5-6kg, which is lighter than silencers made of stainless steel and other materials. The 2000 Chevrolet Corvette Z06 model replaced the original 20kg stainless steel system with an 11.8kg titanium muffler and exhaust pipe system, resulting in a 41% reduction in weight. The strength of the replaced system remains unchanged, making the car faster, more flexible to operate, and fuel-efficient. The titanium material used for silencers is mainly industrial pure titanium.
7. Vehicle 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 good material for manufacturing car body frames, which not only has high specific strength but also has good toughness. In Japan, car manufacturers choose to use pure titanium welded pipes to make body frames, which can provide drivers with sufficient sense of safety while driving.
8. Other titanium alloy components
In addition to the above components, titanium is also used in automotive parts such as engine rocker arms, suspension springs, engine piston pins, automotive fasteners, ear nuts, automotive door protruding beams, automotive gear brackets, brake caliper pistons, pin bolts, pressure plates, transmission buttons, and automotive clutch discs.
The application of titanium alloys
1. Advantages
Titanium alloy has advantages such as light weight, high specific strength, and good corrosion resistance, so it is widely used in the automotive industry. The most commonly used titanium alloy is in automotive engine systems. There are many benefits to using titanium alloy to manufacture engine parts, mainly manifested in:
1) Titanium alloy has a low density, which can reduce the inertia mass of moving parts. At the same time, titanium valve springs can increase free vibration, weaken vehicle vibration, and improve engine speed and output power.
2) Reduce the inertia mass of moving parts, thereby reducing friction and improving the fuel efficiency of the engine.
3) Choosing titanium alloy can reduce the load stress of related parts, reduce the size of parts, and thus reduce the weight of the engine and the entire vehicle.
4) The reduction of inertia mass of components reduces vibration and noise, improving engine performance.
The application of titanium alloy in other components can improve personnel comfort and the aesthetics of cars. In the automotive industry, titanium alloys have played an immeasurable role in energy conservation and consumption reduction.
2. Application limitations
Although titanium alloy components have such superior performance, there is still a long way to go before titanium and its alloys are widely used in the automotive industry. The reasons include high prices, poor formability, and poor welding performance.
With the development of near net forming technology of titanium alloys 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 their application. The main obstacle to the widespread application of titanium alloys in the automotive industry is still the high cost.
Whether it is the initial smelting or subsequent processing of metals, the price of titanium alloy is much higher than that of other metals. The cost of titanium parts that the automotive industry can accept is 8 to 13 US dollars/kg for connecting rods, 13 to 20 US dollars/kg for air valves, and less than 8 US dollars/kg for springs, engine exhaust systems, and fasteners. At present, the cost of parts produced using titanium materials is much higher than these prices. The production cost of titanium sheets is mostly higher than $33/kg, which is 6-15 times that of aluminum sheets and 45-83 times that of steel sheets.
Current research status of titanium alloys for automobiles
Currently, cost reduction is the main research direction for titanium alloys used in the automotive industry. In response to the cost distribution characteristics of titanium alloys used in the automotive industry, material research and development workers mainly aim to reduce 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 inexpensive alloy elements and alloy design improving processing characteristics. Representatives include Japan and the United States, and China has also successfully developed two low-cost titanium alloys, namely Ti8LC and Ti12LC. In the design of low-cost titanium alloy components for automobiles, cheap alloy elements commonly used include Fe, Cr, Si, Al, etc.
2. New processing and preparation technologies
The processing cost of titanium alloy materials accounts for over 60% of the total cost in the production process. Therefore, in terms of cost reduction, how to reduce the processing cost of titanium alloys has become a key research direction. The research in this area is mainly divided into two aspects: one is to improve traditional casting and forging processes, and the other is to use powder metallurgy near net forming technology.
In the development of new forging processes, cold forging is currently one of the most hopeful methods for manufacturing automotive parts using titanium alloys. β Titanium alloy has low deformation resistance at room temperature, good cutting and forming, and can be used for cold forging. Currently, Japan has developed three types of cold deformation materials β Titanium alloy. β Titanium alloy also has some shortcomings, as it is prone to uneven deformation and adhesion to the mold during cold forging. Therefore, cold forging technology is used for mass production β Further exploration and development are needed for titanium alloy components.
Powder metallurgy is an important technology in reducing the processing cost of titanium alloys. In the manufacturing of powder metallurgy automotive parts, traditional pressing sintering methods still dominate, mainly including elemental powder method (BE) and pre alloyed powder method (PA). At present, the elemental powder method is 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, which have been widely used in the trial production and production of complex automotive components, greatly shortening product development and production cycles, and further reducing costs.
epilogue
The new generation of car design places greater emphasis on lightweight body, low fuel consumption, low engine noise and light vibration to meet the increasingly stringent requirements of the environment. In this context, light metal titanium will become a major choice material for future automotive applications.
Taking into account the current research status of low-cost titanium alloys for automobiles, it can be found that in order to further reduce the cost of titanium alloys for automobiles, research should mainly focus on the following aspects:
1) In the development of low-cost alloy systems, efforts should be made to develop alloy systems that do not require or use expensive alloy elements as little as possible without affecting performance, while fully utilizing recycled titanium alloys.
2) In terms of casting and forging process development, we aim to β Develop the direction of titanium alloys and cold deformed titanium alloys, and conduct feasibility studies on their mass production.
3) In powder metallurgy, while ensuring low-cost advantages, it is also necessary to further improve the performance of titanium parts.
With the development of the economy and the reduction of titanium costs, more engineering designers will choose titanium parts as automotive components. Titanium alloys will eventually occupy an important position in the automotive industry production.
