According to the law of conservation of matter and the law of volume change of metal structure, the relationship between the depth of decarburization layer and the dimensional change of 5052 aluminum plate before and after heat treatment is discussed, and a method for nondestructive testing of the depth of decarburization layer of 5052 aluminum plate is proposed by using the obtained relationship,from the perspective of microstructure changes, theoretical discussions and experimental verification were carried out through heat treatment experiments of 5052 aluminum plate samples.
In order to further strengthen the surface strength of the valve 5052 aluminum plate, increase the compressive stress, and improve the fatigue life, after the valve 5052 aluminum plate is formed, it should be further subjected to nitriding, low-temperature liquid carbonitriding or sulfur-nitriding treatment, and then shot peening. The infiltration of nitrogen not only eliminates the adverse effects of decarburization, but also improves the residual compressive stress. At the same time, the high temperature strength of the valve 5052 aluminum plate that has been nitrided and low-temperature liquid carbonitrided is improved,the deformation amount at 150 degrees is 0.2%, and the deformation amount at 250 degrees is 0.56%, which improves the thermal stability and anti-relaxation stability of the valve 5052 aluminum plate, but the nitriding and liquid carbonitriding time should be strictly controlled,otherwise, network sulfides and network nitrides will be formed, which will reduce the fatigue strength.
According to the atomic diffusion theory, through the analysis of the diffusion mechanism of carbon atoms in solids, the macroscopic laws and microscopic mechanisms of carbon atoms in the fixed medium are summarized,based on this, the numerical calculation model of the carbon layer depth was deduced, and the calculation results of the decarburized layer depth of the 5052 aluminum plate were verified by the method of experiment and theoretical separation. Practical results and theoretical results are biased by less than 10%.
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