The applications of titanium and titanium alloy on automobiles

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The applications of titanium alloy on automobiles and its specialty

Titanium alloy is a kind of new structure and function material which has excellent comprehensive performance, low density and high specific strength. The density of titanium is 4.51g/cm3 which ranges between the density of aluminum (2.7g/cm3) and iron (7.6g/cm3). Titanium also has higher specific strength than aluminum alloy and steel and same tenacity with steel. Titanium and titanium alloy have good corrosive resistance which is better than stainless steel, especially in the marine atmospheric environment, it can resist the chloride erosion and under micro oxidizing atmosphere, it will have good corrosion resistance. Titanium alloy has wide operating temperature, for example, cryogenic titanium alloy can still keep good plasticity at -253 degrees Celsius, while the operating temperature of heat resistant titanium alloy can reach to about 550 degrees Celsius, which shows that its heat resistance is obviously higher than aluminum alloy and magnesium alloy. Meanwhile, it also has good machinability and welding performance.

The excellent performance of titanium and titanium alloy has caught a lot of attention to many advanced industry since titanium began its industrial production. With the start of titanium industry, titaniumtim entered the automobile industry in the mid 1950’s. Since 1990’s, due to the global energy shortage and the strenghthening of people’s environmental protection consciousness, especially in the automobile industry, the United States, Japan, European and other countries successively issued a series of ecological laws and regulations in which the higher requirements are put forward on the fuel efficiency, CO2 emissions, vehicle weight loss, the safety and reliability of automobile, etc. Many developed countries and famous automobile manufacturers all actively develop and increase the research and invest on the automotive use of titanium, which will provide strong impetus on the automotive use of titanium. China’s titanium industry also has gradually stepped into the automobile field since 21st century.

In current automobile market, titanium parts are also increased by year with the increasing demand of luxury cars, sports cars and racing cars year by year. In 1990, the global automotive use of titanium was only about 50 tons/year, in 1997 the use was 500 tons/year, in 2002 the use was 1100 tons/year and in 2009 the use was 3000 tons/year. It can be seen that the application of titaniumtim on automobile industry has entered the acceleration stage.

Titanium parts used on automobiles

The main usage of titanium on automobiles can be divided into two categories: firstly, it can reduce the mass of internal combustion engine reciprocating motion piece (for the internal combustion engine parts that has reciprocating motion, it is important to reduce even a few grams of mass); secondly, it can reduce the total mass of automobiles. According to the design and material characteristics, titanium is mainly distributed in the engine components and chassis parts in the new generation automobiles. In the engine system, titanium can be made into valves, valve springs, valve spring sockets, connecting rods and other parts; in the chassis parts, it can be mainly made into springs, exhaust systems, semiaxis, fastenings and so on.

According to the data, except for the above important point, titanium also has other usage on automobiles: the rockers of engine parts, suspension springs, turbine rotors, fasteners, trunnion nuts, bumper brackets, brake caliper piston, pin plugs, clutch discs, pressure plates, variable speed buttons and so on.

Approaches to reduce the titanium alloy cost

Although titanium and titanium alloy entered the automobile manufacturing field in 1950’s, it still develops very slowly due to the price factor. In order to meet the demand of titanium on automobile industry, titanium manufacturers do a mountain of work on smelting, processing, manufacturing and other aspects.

Metal titanium has very high melting point and active chemical property. It has very strong chemical affinity with O, H, N, C and other elements, which leads to the difficult extraction of pure titanium. Titanium sponge is often produced by using Kroll magnesium reduction process in the industry, but it has complex process, high energy consumption and long cycle length, besides, it cannot conduct continuous production and needs a lot of magnesium as reducing agents. Its production cost is also high.

High price of alloying element is another factor that causes the high price of titanium.

With the progress of titanium smelting technology, the effective ways of reducing raw material cost mainly include disposing the defective materials such as offcut and sweeps that are generated in the production and processing procedure of titanium and using them as furnace charge, which will implement the cycle production. Practice also shows that by using 1 percent of residual titanium, the titanium ingot production cost can be reduced by 0.8 percent. If the smelting is conducted in electron beam cold hearth melting and plasma cold hearth melting furnace, the metallurgy quality of titanium ingots will be improved as well as using a large number of recycled furnace charge and reducing the cost of ingot casting effectively.

Reducing finished cost

The finished cost which occupies more than 60 percents of total cost has become the studying focus of the countries to reduce the cost. In the production process of titanium parts, due to the   complex process, large amounts of residual titanium generated in the process and its long production cycle, the units production cost is increased, which will hinder its wider popularization and application.

Casting is a kind of (near) net shape technique, in which the parts is produced without machining or has few machining, thus it will save a lot of metals. The parts produced by traditional process method will have more complex process and higher production cost compared with parts   produced by casting and having complex shape, especially for the titanium that has high material price. At present, titanium castings are used a lot in the aviation industry. In the automobile industry, parts produced by casting method include valves, turbochargers and so on.

Powder metallurgy, served as a kind of advanced technology of modern metallurgy and material processing, has played an important role in titanium industry. By using titanium powder metallurgy near shape technique, the finished products parts or the parts that are close to finished size can be directly made, which will reduce raw material consumption, shorten the processing cycle and save 20 percents to 50 percents of the cost compared to conventional process. In the automobile industry, titanium powder metallurgy near shape technique is especially important. In Japan, the automobile powder metallurgy parts are widely used in engines and gearbox. Among them, connecting rods, valve seats, valves, belt wheels, synchronizer hubs and synchronizing rings are all the critical parts that are complex and have high requirements. Currently the titanium powder metallurgy research is under rapid development stage which mainly includes several aspects: the first aspect is about the preparative technique of producing high quality and low cost titanium powder and its industrialization; the second aspect is about the preparative technique of producing titanium powder and its application on automobile industry.

Except for the above technology, the laser forming technology (intergrating the latest achievements of laser technique, CAD/CAM technique and materials technology) can one-step form the final parts that has complex shape by directly using the alloy powders based on the computer models. The performance of titanium parts generated by this technique ranges between casting and forging, besides, the cost is reduced in the range of 15 percents to 30 percents and the delivery time is shortened in the range of 50 percents to 70 percents. Metal powder injection molding technology (MIM) is a kind of titanium powder metallurgy (near) net shape technique that develops fast, which can be used to make high quality and high precision complex parts and is also regarded as one of the molding technology that has most advantages; besides, the titanium coating technology is also a kind of new technique that can reduce cost. It can be seen that in order to reduce the titanium material cost, we should start from developing new alloy system which has low cost and improve the production process, thus we can truly solve the automobile demand of titanium problem that caused by the high cost of titanium material, in addition, the application of titanium on automobiles will become more competitive and have better development prospects.