Alloy requirements for automobile aluminum castings

Compared with iron and steel, aluminum alloy has many advantages, but it also has some disadvantages, such as its specific heat capacity is almost twice that of cast iron, the latent heat of solidification is 1.4 times that of cast iron, the wear resistance of the commonly used aluminum silicon alloy is much lower than that of cast iron, the coefficient of linear expansion is much higher than that of cast iron, etc. Therefore, the choice of aluminum alloy in modern automobile manufacturing should be considered comprehensively. 62% – 73% of the global aluminum casting output is used in the automobile industry.

It is required that the aluminum alloy casting engine block has good high temperature performance, strong wear resistance, low coefficient of thermal expansion and good fluidity. Because the cooling channels of cylinder and cylinder head contact with water and the surface of combustion chamber of cylinder head is eroded by high temperature gas, it is required to have strong corrosion resistance and high thermal fatigue strength to withstand the fatigue damage caused by thermal shock.

At present, the 390 type alloy which is a kind of Al Si Cu system alloy is used most in engine casting. Silicon and copper are the most important elements in the aluminum alloy of engine. Silicon improves the wear resistance of aluminum alloy. The higher the silicon content, the better the wear resistance of aluminum alloy. At the same time, it can also improve the fluidity of the alloy. But too high silicon content makes casting and processing difficult. Therefore, the silicon content should not only be considered to make the alloy wear-resistant, but also to have good castability and processability. The w (SI) of 390 aluminum alloy is controlled between 16% and 18%, and the properties of service and process are excellent. In aluminum alloy, copper element can improve the strength and hardness of the alloy, and improve the heat treatment performance of the alloy. The room temperature strength of 390 aluminum alloy is the highest when w (Cu) is 4% ~ 5%, and w (mg) is 0.45% ~ 0.65%. Even when the engine temperature is over 260 ℃, the strength of 390 aluminum alloy remains unchanged. Copper reduces the corrosion resistance of the alloy. Therefore, the corrosion inhibitor should be added to the cooling water.

The results show that the yield strength of 390 aluminum alloy is higher than that of 319 and 380 aluminum alloy. The physical properties of 390 aluminum alloy are compared with that of some alloys. Its thermal conductivity and expansion coefficient are better than those of other alloys.

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