MMC is mainly used for aluminum matrix composites reinforced by particles and short fibers in the automobile industry. MMC has been widely used in industry due to its high specific strength and stiffness, good wear resistance, good thermal conductivity and low coefficient of thermal expansion. MMC used in automobile industry is reinforced by aluminum or magnesium matrix plus powder or scrap fiber. MMC is used for manufacturing brake discs, brake drums, brake calipers, pistons, transmission shafts and tire bolts.
At present, aluminum-silicon alloy is generally used for aluminum-based composites. Commonly used filling and reinforcing agents include ceramic fibers and particles. Compared with aluminum alloy, it has the advantages of light weight, high specific strength, high elastic modulus, good heat resistance and wear resistance, and is an ideal material for automobile lightweight.
Piston is one of the main parts of the engine. It works under high temperature and high pressure, so it is very important to select the appropriate piston material. At present, composite materials used in piston are composed of low density metal and reinforced ceramic fiber, mainly used in high-performance aluminum piston. In recent years, fiber reinforced metal (FRM) has been developed. Aluminum alloy based FRM has high tensile strength, wear resistance and heat resistance. Fiber reinforced light metal can be used in parts where the strength and wear resistance cannot be met by light alloy alone, and it is a promising material. On this basis, the aluminum piston with aluminum fiber reinforced piston crown and the piston made of aluminum oxide reinforced magnesium alloy were introduced outside the enclosure, further expanding its application in piston.
The United States has applied aluminum matrix composites to brake wheels. Its characteristics are that the aluminum matrix composite material reduces the mass by 30% - 60%, has good thermal conductivity, the maximum service temperature is 450 ℃, and its thermal performance has reached the level of the original cast iron. MMC must be manufactured in a new way. The principle of limiting application is to develop a matching brake pedal. When the brake caliper is made of metal matrix composite material, in addition to reducing the mass, the most important benefit is stiffness. MMC brake caliper is used in high-performance sports racing, but its high cost limits its extensive application. MMC piston is mainly used in diesel engines, but it can also be used in gasoline engines. Due to the reinforcement of alumina and silica short fibers, thermal fatigue is easy to cause fracture. Using ceramic fiber preform can weaken this problem and improve piston life.
The tyre bolts are made of MMC, with a mass reduction of 50%. In 2000, the consumption of metal matrix composites by the world automotive industry reached 6000 tons. With the continuous improvement of the preparation technology and performance of composite materials, as well as the decreasing price, MMC will be more and more widely used in the steam industry.