In recent years, with the increasingly prominent global climate warming and energy issues, governments of all countries require automobile manufacturers to reduce product energy consumption and pollution. Therefore, major automobile companies in the world are making great efforts to improve the economic performance of their vehicles, reduce fuel consumption and emissions, so as to meet the increasing regulatory requirements. As the heart part of the automobile, reducing the mass of the engine is an indirect way to save fuel. In light materials, cast aluminum alloy is widely used in automobile engine parts because of its advantages of small density and high specific strength.
As one of the heaviest parts of the automobile engine, it is the general trend to replace the original cast iron with cast aluminum alloy to reduce the weight. In the automotive transmission system, about 100% of the pistons, 75% of the cylinder heads and 85% of the intake manifolds are made of cast aluminum alloy.
The wide application of cast aluminum alloy in automobile can be seen from the figure. At present, aluminum alloy is widely used in the field of automobile engine because of its significant role in realizing lightweight, reducing energy consumption and reducing environmental pollution. In particular, China has launched the development and industrialization of aluminum alloy materials in the key program and 863 and 973 programs, which is related to the application prospect of aluminum alloy, and also puts forward higher requirements for the performance of aluminum alloy.
With the rapid development of automobile industry, the high temperature strength and heat-resistant fatigue ability of traditional cast aluminum alloy materials are close to the limit state, which can not meet the needs of engine development. For example, as one of the key components in the engine combustion chamber, the piston needs to contact with 350-400 ℃ high temperature gas for a long time and bear the thermomechanical fatigue effect of 25-300 ℃. Therefore, the development of high-performance cast aluminum alloy with high thermal conductivity, excellent high temperature strength and good dimensional stability is an important research topic in recent 20 years.
According to the existing research results, there are three ways to improve the high temperature properties of cast heat-resistant aluminum alloy:
(1) By means of optimizing the alloy composition, heat treatment process and solidification conditions, the grain size of the alloy matrix structure, the formation of thermally stable co lattice and semi co lattice precipitates and the control of the distribution, morphology and volume fraction of these nano precipitates are regulated, and the multi-scale and multi factor composite strengthening is realized by means of precipitation strengthening and dispersion strengthening.
(2) By adding nano particles or fibers to the aluminum matrix, the dislocations and grain boundaries are pinned to prevent the dislocation sliding, climbing and grain boundary moving during the high-temperature deformation process, so as to improve the material resistance.
(3) Rare earth elements or transition metal elements are added to the cast aluminum alloy as the main elements. By increasing the contact area between the primary Si and eutectic Si phases and the intermetallic compounds, the transfer ability of high-temperature download load from the matrix to the reinforced phase is increased, and the heat resistance of the material is improved.
With the global shortage of energy and resources and the increasing attention to environmental protection, the rapid development of the automobile industry, the growing demand for high-performance materials used in engines, high-strength heat-resistant cast aluminum alloy is bound to get more and more attention, research and use. Therefore, it is necessary to integrate the basic research advantages of universities and scientific research institutes with the product R & D advantages of enterprises, develop efficient, practical and economic cast aluminum alloy as soon as possible under the guidance of market demand, occupy the advantages of international aluminum resource technology integration, and promote the vigorous development of China’s aluminum industry.