Application Of Titanium Alloys in Lightweight Automobile Manufacturing
Titanium and titanium alloys have the characteristics of low density, excellent mechanical properties, good biocompatibility, corrosion resistance, high temperature resistance, and good low-temperature toughness. They have been widely used in the field of automobile manufacturing. The density of titanium alloy is only 60% of that of steel, while the strength can reach more than 800MPa. It still maintains good mechanical properties at around 500℃, and has good welding and forming properties. It has been used in the manufacture of racing cars more than 20 years ago, greatly reducing the weight of racing engines and improving engine performance.
At present, titanium alloy parts used in automobile manufacturing are mainly distributed in automobile exhaust systems, engine systems, transmission and vibration reduction systems, and body frames.
1. Exhaust system
The materials of automobile exhaust systems are required to have good high-temperature mechanical properties and resistance to corrosion by S and Cl elements. Traditional exhaust valve components are made of stainless steel, but people have found that titanium alloys are more suitable for use as exhaust valve materials in terms of performance.
The titanium return pipe used in the new Chevrolet Corvette Z206 effectively avoids the pitting and weld rust problems that occur on stainless steel pipes, while also improving fuel combustion efficiency and acceleration capabilities, and shortening braking distances.
Timet, the largest titanium manufacturer in the United States, has been committed to the research and development and manufacturing of titanium alloy exhaust systems. Many Japanese companies have also carried out related research and development work. At present, Fuji Heavy Industries, Ltd. has limited production of 440 sets of titanium alloy automotive exhaust pipes.
2. Engine system
The automobile engine system is the part that uses the most titanium alloy in the automotive field. The application of titanium alloy in the engine system mainly includes valves, connecting rods, crankshafts, valve seats and other parts.
Honda Motor Corporation of Japan uses forged titanium connecting rods in the NSX racing V-6 engine; Mitsubishi Motors uses titanium valve spring seats in high-capacity, four-cylinder engines, and titanium connecting rods are also used in Porsche cars.
(1) Valve
In terms of titanium alloy valves, the United States and Japan have conducted a lot of research work. The United States currently generally uses Ti-6Al-4V alloy to make intake valves and Ti-6Al-2Sn-4Zr-2Mo alloy to make exhaust valves; while Toyota of Japan uses Ti-6Al-4V/Ti B alloy to make intake valves and Ti-Al-Zr-Sn-Mo-Nb-Si/Ti B alloy to make exhaust valves. These types of titanium alloys have good high-temperature mechanical properties, oxidation resistance and creep resistance, which effectively improve engine performance and increase vehicle speed.
(2) Valve seat
Titanium alloy valve seats have been widely used in racing cars and sports cars, with an annual production of more than 250,000 sets. They are mainly made of Ti-6Al-4V or Ti-5Al-2Cr-1Fe alloy. Since the shape of the valve seat is relatively simple, it does not require high requirements in terms of machining and does not require special surface treatment. It is relatively cheap and has a significant effect on reducing the weight of the car.
(3) Connecting rods
The use of titanium alloy connecting rods can effectively reduce the weight of the engine and improve the performance of the car. The main preparation material is Ti-6Al-4V alloy. Japan's Daido Co., Ltd. is currently developing a two-phase titanium alloy Ti-3Al-2V-0.2Si-0.47Ce-0.27La. This alloy has good machinability and is also excellent in mechanical properties, fatigue properties and corrosion resistance. It is expected to be used in the connecting rod parts of the engine that are subject to rapid acceleration and deceleration.
(4) Crankshafts
Although titanium alloy crankshafts have not been widely used at present, the Ti-3Al-2.5V alloy specially developed by Japan has been verified on Honda racing cars. While effectively reducing the weight, it has increased the engine speed by 700r/min, proving the superiority of titanium alloy crankshafts. At the same time, Japan has been trial-producing Ti-5Al-2Cr-Fe alloy crankshafts, hoping that titanium alloys will be more widely used in crankshaft parts.
3. Vibration reduction system
The core component of the automobile vibration reduction suspension system is the suspension spring. Compared with general automobile spring steel, titanium alloy has higher specific strength and lower shear modulus, and higher fatigue strength, making it more suitable for manufacturing automobile shock-absorbing springs. Since the deflection of the spring is proportional to the number of turns and inversely proportional to the shear modulus of the material, titanium alloy springs require fewer turns than steel springs to achieve the same spring response, effectively reducing the spring mass and saving space.
At the same time, titanium alloy springs can also effectively increase the resonant frequency of the spring and increase its service life. At present, most titanium alloy springs are made of single-phase β titanium alloy. Volkswagen has used Lupo FSI titanium alloy gear springs on some cars, with a usage of about 3,500 vehicles.
4. Body frame
In terms of body frame components, titanium alloy's higher specific strength, lower density and good corrosion resistance all indicate that it is a good material for preparing body frames. At present, some automobile companies have used titanium alloys on parts such as gear brackets and brake caliper pistons. Among the transmission parts, Japan is currently developing a process for preparing titanium alloy shells by high-speed spinning. Compared with steel shells, titanium alloy shells can better reduce the impact of flywheels and have better buffering effects.
In addition, titanium alloys have also been used in automotive fasteners and other parts. With the continuous development of titanium alloy preparation technology and the automotive industry, titanium alloys will surely be used more in automotive parts.
5. The significance of titanium alloys to lightweight vehicles
Foreign research institutions have calculated that when the curb weight of a car decreases by 10%, fuel consumption can be reduced by 6% to 8%. Other studies have shown that for every 91kg weight reduction, the average vehicle can travel 0.43km more per liter of fuel. Therefore, with the continuous development of my country's economy and the continuous increase in the number of cars, lightweighting of cars has become one of the important ways to reduce energy consumption and reduce air pollution.
Titanium and titanium alloy materials are currently widely used in automotive parts due to their excellent physical and chemical properties. The use of titanium materials not only effectively improves the performance and safety factor of the car, but also plays an important role in lightweighting the car, effectively reducing the curb weight of the car and reducing fuel consumption.
Compared with the traditional stainless steel system, the titanium tail nozzle-return pipe assembly used in the automobile exhaust system can reduce the weight by about 8.2kg. The use of titanium alloy products instead of traditional steel and cast iron materials in the engine parts such as valves and connecting rods can effectively reduce the weight of the engine.
According to research in the Japanese automobile industry, the use of about 0.8kg of titanium parts in the power valve of an automobile is equivalent to the effect achieved by 20kg of steel parts; each titanium valve seat can reduce the weight of about 10g compared with the steel valve seat; the use of titanium alloy for connecting rods and crankshafts is most effective in reducing the weight of the engine.
In the vibration reduction system, each titanium alloy spring can reduce the weight of more than 60% compared with the steel spring. Calculated based on 4 suspension springs per vehicle, after replacing the titanium alloy spring, each vehicle can reduce the weight by 9~13.6kg. In addition, the weight of the titanium alloy muffler is only 5~6kg, which is 40% lighter than the stainless steel muffler.
Taking an ordinary mid-sized car as an example, if the existing titanium alloy auto parts are used to replace the traditional parts, the vehicle's curb weight will be reduced from about 1500kg to about 1000kg, with a weight reduction rate of 30%, and the comprehensive fuel consumption can be reduced by more than 20%, which will greatly reduce the world's fuel consumption and effectively alleviate the problems of energy shortage and environmental pollution.
The above data show that the use of titanium alloys has a significant effect on lightweighting of automobiles. In the modern automobile industry, the application technology of titanium and titanium alloys in automobile parts should be continuously developed to increase the application ratio of titanium alloys in automobiles. Therefore, the main task in the future should be to reduce the price of titanium alloy parts by developing cheap titanium alloy materials and reducing the production cost of titanium alloy raw materials, and to improve the processing efficiency of titanium alloy parts by improving the processing technology.
