Today, cars have a history of over a hundred years and are an indispensable means of transportation in our daily lives. The lightweight and high-strength properties of titanium have long been a focus of attention for automobile manufacturers. Titanium valley titanium has been used in racing for many years, and almost all current racing cars use titanium materials. However, the general automotive industry is an emerging market for titanium development.

The advantages of using titanium as a material for automotive components include high strength, low density, elastic modulus about half that of steel, low coefficient of thermal expansion about half that of stainless steel and aluminum, non-magnetic, low thermal conductivity, and no pollution to the environment. In addition, the use of titanium in the automotive industry can greatly reduce the weight of cars, lower their fuel consumption, improve their work efficiency, and reduce noise.

1. Application of titanium alloy in automobiles

Typical titanium alloy parts on automobiles include rotor blades of turbine chargers made of TiAl, connecting rods, valves, etc. made of Ti-6A1-4V alloy, etc. In order to achieve cost reduction, TiB particle dispersed titanium based MMC was added to the Ti-6A1-4Sn-4Zr-1Nb-1Mo-0.2Si-0.3C alloy matrix using powder metallurgy method to manufacture engine valves. In addition to connecting rods and engine valves, the suspension spring made of low-cost β - type titanium alloy TImetalLCB was also the initial application example. Recently, progress has been made in the development of low-cost titanium alloys for engine valves and exhaust. Especially with the increasing demand for titanium alloys in the exhaust system (muffler) of motorcycles, the development of low-cost alloys for exhaust systems has become more popular at the Titanium Valley Nonferrous Metals Trading Center.

Table 1 Application Status of Titanium Automotive Standard Components



In 1956, General Motors (GM) and its suppliers assembled an ideal exhibition car with a body made entirely of titanium. Since then, GM has been wanting to use titanium in engines, including exhaust valves and connecting rods. At present, some car manufacturers have used small amounts of titanium parts in certain models of cars. Titanium Valley Nonferrous Metals Trading Center, such as Honda Motor Company in Japan, used forged titanium connecting rods in the NSX racing 3.0L24 valve V-6 engine in 1994; The high-capacity, four cylinder engine manufactured by Mitsubishi Motors uses titanium valve spring seats; Porsche cars also use titanium connecting rods. With the increasing development of titanium, it has been widely used as a high-end automotive component for special purposes in automobiles.

1.1 Valve

Using titanium alloy to make car valves not only reduces weight and extends service life, but also has high reliability and can save fuel. The exhaust valve should not only be heat-resistant and wear-resistant, but also free of lead and cobalt. It is common for American manufacturers to use titanium alloy to make intake and exhaust valves. The intake valve uses Ti-6A1-4V alloy, while the exhaust valve uses Ti-6A1-2Sn-4Zn-2Mo alloy. The sintered intake valves manufactured by Hitachi in Japan have been supplied to the automotive industry market in Japan.

Howmet Foundry Company in the United States produces valves using continuous casting method, with each valve containing 1/4 of its weight in titanium. It is estimated that there is a potential market of 200 million valves per year for new cars, and an annual replacement market of 80 million valves.

1.2 Valve seat

The most widely used titanium component in racing and sports cars is the valve seat, which is produced over 250000 times a year and is generally made of Ti-6A1-4V alloy. Japan also uses Ti-5A1-2Cr-1Fe alloy for production. Due to its simple and compact shape, mechanical additive manufacturing is easy and cost-effective. It does not necessarily require special surface treatment, and compared to steel valve seats, it can reduce weight by 10-12 grams.

1.3 Connecting rod

Using titanium alloy to manufacture connecting rods is the most effective way to reduce engine weight and greatly improve performance. The main material used for the connecting rod is Ti-6A1-4V, while other materials such as Ti-4A1-2Sn-4Mn and Ti-7A1-4Mo are also under development.

1.4. Crankshaft and other engine components

Japan is currently developing Ti-5A1-2Cr-Fe alloy crankshafts, which require anti adhesive treatment and have not yet been put into practical use. Other engine components such as rocker arms, valve springs, and lower bolts of connecting rods can also be manufactured using Ti-6A1-4V alloy.

The free cutting Ti-3A1-2.5V alloy crankshaft specially developed in Japan has been used in the Honda 280 horsepower 3.0-liter V6NSX luxury racing car. Compared with steel crankshafts with the same fatigue strength, it reduces weight by 30% and increases engine speed by 700r/min. These research and application results indicate that titanium has been accepted and its usage has been expanded in racing cars.

1.5. Return pipe

The use of titanium tailpipe/return pipe components is not affected by corrosion caused by the discharge of chloride salts and sulfur in the exhaust gas. The exhaust system does not show pitting corrosion, and even corrosion does not occur at the welding points. Compared with traditional exhaust system materials - stainless steel, the Titanium Valley Nonferrous Metals Trading Center can reduce weight by 40%, while improving fuel economy, with faster acceleration ability and shorter braking distance. Due to the high cost of titanium, the American titanium company Timet has developed a special surface treatment method, which helps produce parts that meet the cost standards of automotive manufacturers. The new Chevrolet Corvette Z06 car has adopted a titanium return pipe.

1.6 Suspension spring

Compared with steel springs used in ordinary cars, titanium springs have light weight, good corrosion resistance, and low shear modulus (which can reduce the turning of spring coils). Timet has developed a titanium alloy specifically to meet the cost and component assembly requirements of automotive suspension spring manufacturers. This material retains the excellent performance of titanium alloy springs used in aviation and greatly reduces costs. The initial production quantity was very small, and it was used for the gear suspension spring of Volkswagen's new Lupo FSI car in Europe. Timet and Volkswagen announced in January 2001 that titanium suspension springs would be used in the 2001 model of Lupo FSI, with an expected production of 3500 units of this model.

Springs made of titanium can reduce weight by 60-70% compared to steel. In a typical American made 5-6 seater family car, by using 4 suspension springs, each car can reduce weight by 9kg to 13.6kg.

1.7 Muffler

The titanium muffler weighs only 5-6kg, which is much lighter than stainless steel and other mufflers, and is easy to operate. The demand for titanium in the Japanese automotive industry (actual demand reached 457 tons in 1999) is mainly used for mufflers, mainly for large cars (above 900cc). Four major Japanese manufacturers, including Honda and Suzuki, have adopted titanium mufflers. Titanium mufflers are mainly used for large cars and some medium-sized cars. The corrosion resistance, strength, and surface finish of titanium are currently being evaluated.

GM has replaced the original 20kg stainless steel system with an 11.8kg titanium muffler and exhaust pipe system on the 2000 Chevrolet Corvette 206 model, while maintaining the same strength. Weight reduction of 41%, increased vehicle speed, flexible operation, and fuel savings.

1.8. Vehicle body and other components

Timet believes that titanium can be used in other forms of components in household vehicles to greatly reduce weight and improve durability, including engine components, drive gear train parts, suspension systems, and structural components. Such as shock absorber center rod, hanging ear nut and bolt, control rod, fastener, driven shaft, gear bracket, door protrusion beam, brake caliper piston, engine connecting rod, pin bolt, valve, valve spring and seat, etc.

Using titanium alloy Ti-6A1-4V to manufacture clutch plates, pressure plates and other transmission components, and recently starting to use high spin forming to manufacture titanium alloy shells, compared with steel shells, can greatly reduce the impact damage of flywheels and make buffering easier. Japanese scholars have designed a new combination sliding die and developed another type of automotive sprocket using bottom punch forming.

1.9 Fasteners

For many types of fasteners, titanium can be used instead of steel. Titanium fasteners are feasible or necessary in future light transportation vehicles.

2. Research status of titanium and titanium alloys for automobiles

2.1 United States

The countries that use the most titanium in cars are the United States and Japan. Firstly, the United States attaches great importance to the application of titanium in automobiles, such as Timet's establishment of a car factory to develop titanium automotive components. Titanium Valley is losing money. The United States has produced titanium intake valves, exhaust valves, valve retainers, connecting rods and other components for racing cars, with 50 tons of titanium used annually for automobiles. In 1996, at the International Titanium Association exhibition held in Las Vegas, Timet showcased its titanium automotive exhaust system made of industrial pure titanium. Subsequently, Chrysler and GM produced a commercial prototype of the pure titanium exhaust system, and large-scale production evaluation is underway. At the same time, GM is also conducting research on Timetal-62S and Timetal-LCB axles, and is considering putting this alloy into mass production. In addition, the high-performance car NSX Acura in the United States also uses titanium connecting rods, which is an example of mass production of titanium for automotive connecting rods. Ford Motor Company has confirmed several titanium alloy components suitable for use in automobiles, including Ti-3A1-8V-6Cr-4Mo-4Zr springs, Ti-6A1-4V intake valves and valve retainers, Ti-6A1-2Sn-4Zr-2Mo, and Ti-6A1-2Sn-4Zr-2Mo-0.1Si exhaust valves. The titanium springs produced by the company around 1989 weighed only one-third of the weight of equivalent steel springs, and were even smaller and more compact. The intake and exhaust valves produced could extend the mileage of a car on a gallon of gasoline by 3-4%. When combined with titanium springs, this valve can reduce the fuel consumption of the engine.

The United States has developed a series of low-cost titanium alloys. Timet and GM have developed Timetal 62S (Ti-6A1-2Fe-0.1Si) alloy for automotive engine components, which has better performance than Ti-6A1-4V and lower cost by 15% to 25% compared to Ti-6A1-4V. The newly developed titanium alloy Timetal Exhaust XT for motorcycle and automobile exhaust systems by Timet Company is a Ti-Fe-Si-O alloy, with the highest mass fraction of alloy elements being 0.5% Fe and 0.6% Si; 0.15% O. The company produced 3.2t flat ingots using electron beam melting, which were hot-rolled and cold-rolled into coils with specifications ranging from 1.65 to 0.91 mm.

The American titanium smelting company has developed the Timetal1100 (Ti-6Al-2.7Sn-4Zr-0.4Mo-0.45Si) alloy exhaust valve, which has creep resistance and oxidation resistance at 6000 ℃. Timet's Timetal LCB (Ti-4.5Fe-6.8Mo-1.5A1) alloy is specially developed to enter the automotive market. Its comprehensive performance is excellent, especially its fatigue resistance, which is superior to any other titanium alloy. Timetal LCB is a low-cost metastable β - titanium alloy, and its main alloying element is the low-cost Fe Mo alloy. The yield strength is higher than 900Mpa and the elongation is about 18%. Its performance is not inferior to high-strength steel. Compared with using aluminum molybdenum intermediate alloys, using molybdenum iron can reduce costs by about 25% to 33%. LCB suspension springs have been used on off highway racing trucks, which not only reduce vehicle weight but also have two advantages: faster response speed than steel springs, making driving smoother; Weight reduced by 60%, volume reduced by 25%, and lifespan exceeding four times that of steel springs. Manly High Performance Products Company in the United States has produced two types of titanium valves, Ti-1000 and Ti-6A1-2Sn-4Zr-2Mo, which have participated in various types of motorcycle races.

2.2 Japan

Japan applied titanium to racing cars and some sports cars as early as 20 years ago, but it has not yet been used for cost conscious general passenger cars. The Nissan R382 won the Japanese Grand Prix due to its use of titanium alloy valves. At present, the applications of titanium and its alloys in automobiles mainly include engine components such as springs, rods, connecting rods, standard parts, wheels, power valves, etc. According to Japan's experience, using 0.8-0.9kg/set of titanium in automotive power valves is equivalent to reducing weight by 20kg/set.

Japan has conducted extensive research on the application of titanium in automobiles. The Future Technology Research Institute has developed titanium alloys for automobiles such as SAT64AW, SAT64HM, SAT325HM, Ti-20V-4A1-lSn, etc. AT64HM and SAT325HM alloys have good hot workability, drillability, and fatigue resistance, and can be used for components such as connecting rods with multiple drilling holes, resulting in lower cutting costs. The Ti-2V-4A1 alloy developed by Mitsubishi Motors in Japan has good cold workability and is suitable for manufacturing valve stems. The intake and exhaust valves made of Ti-6Al-4V by Toda Manufacturing in Japan have improved the performance of the engine and increased the speed of the car by 10-15% due to the Titanium Valley fraud. It is worth mentioning that at the 29th International Automobile Exhibition held in Tokyo, Japan in 1992, titanium body panels and titanium energy-saving and low pollution engine cars were exhibited for the first time, attracting attention from all aspects of the attendees. In 1996, titanium was used on the structural components of solar powered cars manufactured in Japan, and it won a place in the Fourth World Solar Car Championship. Titanium was initially used in the mass-produced high-end car NSX V-6, followed by the valve class of the Toyota two door convertible sedan that won an award in Japan in 1998. The intake valve of the car uses Ti-6A1-4V/TiB alloy produced by powder metallurgy method, and the exhaust valve uses heat-resistant Ti Al Zr Sn Nb Mo Si/TiB alloy. The engine of this car is 2000cc, equipped with one 279 intake valve and eight 249 exhaust valves. The total weight of titanium used in one car is 408g. When the raw material is steel, the weight of each is 40.Og and 44.6g, respectively. The total weight of the valves is more than twice that of titanium. The valve springs of this car also use titanium, reducing its weight from 43g to 36g. Toyota initially produced 4000 units of this new type of car, half of which were made of titanium.

Japan's Daido Steel Company has developed a new type of titanium aluminum alloy, which can be used to manufacture exhaust valves for automotive engines and greatly improve engine performance. The composition of this new titanium aluminum alloy is Ti-33.5A1-1Nb-0.5Cr-0.5Si (wt%), in which Nb and Si are added to improve the oxidation resistance and creep resistance. Compared with the commonly used martensitic heat-resistant steel and nickel based alloys for exhaust valves, the outstanding feature of this alloy is its small specific gravity (only half of martensitic heat-resistant steel) and good thermal conductivity. The Japan Institute of Metal Materials and the Korea Institute of Machinery and Metals have collaborated to use element mixing method to uniformly mix alloy powder and strengthening powder, vacuum sintering, and hot isostatic pressing to produce two low-cost alloys with excellent tensile, creep, and fatigue properties, which are expected to be used to make automotive parts.

The characteristics required for titanium alloys used in automotive exhaust systems must meet the following four points: (1) sufficient strength at high temperatures above 600 ℃, with little decrease in strength after long-term use. (2) The reduction in wall thickness caused by oxidation at high temperatures above 700 ℃ is very small. (3) At room temperature, it has the same or higher formability (bending, bulging characteristics, deep drawing, etc.) as JIS Class 2 and ASTM Gr.2 pure titanium (hereinafter referred to as Gr.2). (4) At high temperatures above 600 ℃, a certain load with a yield strength below 0.2% of the temperature is difficult to deform even when applied for a long time, indicating excellent creep resistance. The design concepts and excellent characteristics of Ti lCu and Ti-1Cu-0.5Nb for automotive exhaust systems developed by Nippon Steel Corporation in Japan, including room temperature formability, high temperature strength, oxidation resistance, and creep resistance. These alloys have achieved low oxidation through the addition of Cu, and the necessary addition of Nb has given rise to new concepts that were not originally thought of in alloy design, such as Super TIX 10CU and Super TIX 1OCUNB, which have been widely used as automotive exhaust system materials. Since 2007, Super TIX 10CU has been used in parts of Suzuki GSX series mufflers that require heat resistance. It has been used in Nissan GT-Rspec-V since 2009 and in GT-R EGOIST mufflers since 2010 (Figure 1 (a)), with a weight reduction of approximately 30% compared to stainless steel. Super TIX 10CUNB, the largest exhaust system component manufacturer in Europe, Akrapovic not only uses it on motorcycles, but also on some parts of car mufflers (Figure 1 (b)), fully utilizing the high workability, high temperature strength, high oxidation resistance, and creep resistance of these alloys at room temperature. The alloy design and manufacturing conditions are set appropriately.

2.3 China

China is vigorously promoting the use of titanium in automobiles. Firstly, through websites, newspapers, magazines, and promotional events, knowledge of titanium applications will be disseminated to every corner of society, and then titanium will be linked to automobiles to promote its application in the automotive industry. The research on titanium for automobiles has been ongoing, such as the study of powder metallurgy titanium and TiAl.