Automotive materials mainly contribute to the improvement of fuel economy through light weight of automobiles. Both theoretical analysis and experimental results show that lightweight is an effective way to improve the fuel economy of automobile. In order to meet the requirement of lightweight, some new materials came into being and expanded the scope of application.
In passenger cars, the proportion of nonferrous alloys used in each car in 1973 was 5%, up from 5.6% in 1980, compared with 9.6% in 1997. The rapid growth of the use of non ferrous alloys in automobiles is a major trend in the development of automotive materials.
The density of aluminum is about 1/3 of steel, and it is the most widely used lightweight material. Automotive products in the United States, for example, were only 39kg per vehicle in 1976 and 62kg in 1982, compared with 100kg in 1998.
(1) cast aluminium alloy
Many kinds of elements can be used as alloy elements for casting aluminum alloy, but only Si, Cu, Mg, Mn, Zn and Li are important in mass production. Of course, it is not the simple two element alloy that is widely used in automobiles, but many kinds of elements are added at the same time to obtain good comprehensive properties.
The automotive industry is the main market for aluminium castings, such as Japan, 76% of aluminium castings, and 77% of aluminium die castings for automobile castings. Aluminum Alloy casting is mainly applied to the engine cylinder body, cylinder cover, piston, intake manifold, rocker arm, engine mounting bracket, connecting rod, clutch shell, air compressor clutch, brake parts, wheels, handles and cover shell parts etc..
There are unavoidable defects in aluminum castings, and die castings can not be heat treated, so they are limited in the production of high strength castings with aluminium alloy. Therefore, the casting process has been improved. Casting, forging and semi-solid forming will be used in the future.
(2) wrought aluminium alloy
The deformation of Aluminum Alloy refers to Aluminum Alloy strip, extrusion and forging materials, mainly used in automotive body panels on the body frame, engine, radiator, air conditioning condenser, evaporator, wheels, trim and suspension parts.
Due to the obvious lightweight effect, the application of aluminum alloy on the body is expanding. For example, the Japanese Honda NSX, which began selling in September 1990, uses a fully aluminum bearing body, which is lighter than 200kg made from cold rolled steel plates, and attracts worldwide attention. The use of aluminum reached 31.3% NSX in the whole car, such as aluminum body, the outer plate using the 6000 series alloy, 5052-0 alloy panels, frame use 5182-0 side frame high alloy; because of the strength and stiffness requirements using alloy based on 6N01 alloy, appropriate adjustments to the Mg and Si content. In Europe and the United States also useful 2036 and 2008 alloy for the body inside and outside the plate.
Aluminum radiators originated in Europe and then spread all over the world. In Europe, the aluminum radiator had occupied 90% of the market by the late 1980s. With the use of automotive air conditioning and oil coolers, the market for aluminium heat exchangers has expanded rapidly. From a material point of view, the widespread use of aluminum on heat exchangers owes much to the successful development of cladding aluminum and aluminium strips.
(3) aluminum matrix composite
Aluminum matrix composite has low density, high specific strength and specific modulus, good thermal fatigue resistance, but its application in automobile has been restricted by price and production quality control, but it has not yet formed a large scale. At present, the test of aluminum base composite material in connecting rod, piston, cylinder hole, brake disc, brake caliper and drive shaft tube and other parts or show excellent performance, such as Honda Corporation developed by? Aluminum matrix composites reinforced by steel wire rod than steel rod weight reduction of 30%, 1.2L the gasoline engine fuel economy can be improved by 5%; powder and SiC powder chilled Aluminum Alloy (2% weight percent) are mixed and extruded into the bar, the bar by the piston forging for high strength reduced 20%, a substantial increase in engine power; and cancel the austenitic cast iron insert ring groove can be 20% weight reduction of piston head strengthening aluminum matrix composite; disc brake of composite cast iron brake disc 50% weight reduction ratio.
The density of magnesium is about 2/3 of aluminum and is the lightest in the practical metal. Magnesium alloys are suitable for automobile parts because of their high vibration absorption ability, good cutting performance and good casting performance.
Magnesium alloys are mostly used in automobile castings, and the production efficiency of magnesium die castings is higher than that of aluminum alloy 30%~50%. The newly developed Pore Free (Diecast) can produce magnesium die castings without porosity and heat treatment.
The earliest examples of magnesium castings used in automobiles are wheel rims. The trial in the car or the application of magnesium alloy case and clutch, clutch pedal and brake pedal bracket, dashboard frame, seat, steering column assembly, steering wheel core, gear box shell, engine mount, cylinder head and cylinder head cover etc.. With the traditional zinc steering column bracket compared, weight reduction of magnesium parts 65%; and the traditional steel steering wheel core compared to magnesium parts 45% weight reduction; compared with the aluminum cylinder head, weight reduction of magnesium parts 30%; compared with the traditional steel stamping welding structure of brake pedal bracket, the overall drop of Magnesium Castings the weight of 40%, while its rigidity is also improved.
The research progress of magnesium matrix composites is also advanced. The magnesium matrix composites obtained by liquid mixing technology with SiC particles as reinforcement and with liquid mixing technology have good performance and low production cost. Composite metal alloy tensile strength of SiC particles in AZ91 alloy increased 25% increased by 23%, yield strength increased by 47%, the elastic modulus increased by 72%.
The density of titanium is 4.5g/cm3, which has the advantages of high specific strength, high temperature strength and corrosion resistance. Titanium is so expensive that it has been used only in racing cars and in individual luxury cars. Nevertheless, there are many researches on the application of titanium alloys in automobiles. For example, the engine connecting rod alpha + beta titanium alloy manufacture, the level of intensity is equivalent to 45 of quenched and tempered steel, and the weight can be reduced by 30%; beta titanium alloys (Ti-13V-11Cr-3Al) by strong cold work and aging treatment, the strength up to 2000MPa, can be used to make a suspension spring, a valve spring and a valve, compared with tensile strength high strength steel 2100MPa, titanium spring can reduce the weight of 20%.
The biggest resistance to titanium alloys comes from their high prices, and the TOYOTA Central Research Institute developed a lower cost titanium matrix composite. The composite is based on Ti-6Al-4V alloy and TiB is reinforced. It is produced by powder metallurgy and has been applied to engine connecting rod.