Research status of engine block materials

The castings of engine cylinder block, cylinder head and cylinder liner not only have complex structure, various processes, great casting difficulty and high requirements for process equipment, but also have strict requirements for wear resistance and thermal stability. With the development of automobile engine technology, the requirements for the quality, reliability and stability of engine castings are further improved. Coupled with the high cylinder pressure required by low emission regulations, modern engine cylinder blocks put forward higher requirements for material strength and fatigue performance.

The engine is the heart of the automobile. The cylinder block is the most complex and difficult casting in the engine, enjoying the reputation of “flower of casting”. Cylinder block and cylinder head are key parts of automobile engine with large size, complex shape, great difference in wall thickness, very bad working conditions, very high technical requirements and great production difficulty. Therefore, the production technology of cylinder block and cylinder head castings is recognized as the core manufacturing technology in the machinery manufacturing industry. So far, the materials of engine cylinder block and cylinder head are mainly gray cast iron, vermicular cast iron and aluminum alloy. Although aluminum alloy has the advantages of low density and light weight, it has poor stiffness, low strength and high price. The machinability of vermicular graphite cast iron is poor. Gray cast iron is widely used in the manufacture of engine cylinder block because of its good wear resistance, heat resistance, oxidation resistance, corrosion resistance, shock absorption and thermal conductivity. Compared with other alloys, it also has the advantages of low melting point, good filling performance, good processability, convenient production and low price.

At present, the cylinder block and cylinder head of large trucks and tractor engines are made of gray cast iron. With the development trend of high-power and lightweight of vehicles, the strength requirements of cylinder block and cylinder head castings, as the most representative thin-wall high-strength complex iron castings, are becoming higher and higher. However, the biggest disadvantage of gray cast iron is its low tensile strength. In order to improve the strength of gray cast iron, countries all over the world have studied it. In 1997, the American Foundry Association established the thin-walled cast iron group (twig) to improve the technology of high-strength gray iron castings and thin-walled gray iron castings; The Japanese government has also given support to its thin-walled high-strength gray cast iron technology for the 21st century. New casting powers such as Brazil and India also attach great importance to the production quality and technological progress of key castings such as engine cylinder block and cylinder head, and their casting market is very competitive. China began to produce engine cylinder block in the mid-1950s. After decades of development, China can design and develop small and medium-power engines by itself. In 2003, the total output of iron castings in China was 1987 million tons, including 10.49 million tons of gray iron castings, accounting for 53% of the total output. However, due to the small scale, low production socialization level, slow renewal of production equipment, low degree of mechanization, insufficient investment in casting scientific research and development, low achievement conversion rate and uneven quality of casting employees, most of China’s cast iron enterprises affect the popularization and application of contemporary advanced technology and advanced management experience, resulting in casting quality, production efficiency, economic benefits There is still a certain gap in energy consumption, working conditions and environmental protection compared with industrial developed countries. According to statistics, due to the unstable quality of molten iron and other reasons, under the same carbon equivalent, the grade of gray cast iron in China is 1-2 lower than that in foreign countries. Therefore, few domestic high-performance and high value-added iron castings enter the international market. On the contrary, these high-quality castings mainly rely on imports, resulting in the same gray iron castings, and the price difference between China and foreign countries is 3-6 times. Therefore, it is urgent for Chinese foundry workers to speed up the research and development of gray iron castings with high technical content, high added value and strong market competitiveness.

At present, the high-power engine block and other high-strength gray cast iron castings produced in China mainly improve the properties of gray cast iron by adding a certain amount of Cu, Cr, Mo and Ni alloy elements. Among these alloy elements, the price of Cu is relatively low and is the most commonly used. However, with the rise of copper price, in mass production, if the amount of Cu can be reduced or cancelled by adding other alloy elements, improving inoculant or improving smelting process, it will bring huge economic and technical benefits. With the improvement of gray cast iron strength, another urgent problem to be solved in casting production is the machinability of engine block gray castings. Various alloying elements added to meet the service performance of gray cast iron increase the cutting resistance and tool wear of gray cast iron. At present, numerical control machine tools, automatic machining lines and high-speed cutting technology are widely used in car production. The wear and service life of cutting tools have a great impact on production efficiency. Therefore, the cutting performance of gray iron castings has become a technical problem of common concern to engine cylinder researchers at home and abroad.