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Research on eliminating residual stress of aluminum alloy specimens by vibration aging

Abstract: the elimination of residual stress of aluminum alloy components by vibration aging is explored, and the aluminum alloy specimens with rectangular section are selected as the research object. The residual stress is prefabricated by loading, and then excited under certain support conditions. The experimental results show that the residual stress of the specimen is reduced and homogenized after excitation. The work of this paper provides an experimental basis for the study of vibration aging of non-ferrous metal components

key words: vibration aging; Residual stress; Aluminum alloy

introduction

residual stress is a kind of self balanced internal stress existing in metal components. There are many factors that produce residual stress [1, 2], but to sum up, there are mainly two factors. One is the effect of heat, which leads to uneven cooling and internal stress, common ones are casting, welding, heat treatment, etc; The second is the effect of force, which leads to plastic deformation on the surface or inside of metal [3], commonly including metal cutting, loading, etc. The existence of residual stress directly affects the service performance of mechanical parts, reduces the working strength of parts, affects the dimensional stability of parts, and accelerates the fatigue failure of parts [4, 5]. Therefore, the existence of residual stress is undoubtedly a potential danger for metal parts. Due to the harmfulness of residual stress, people eliminate residual stress by natural aging, thermal aging, vibration aging and other methods. Here, the meaning of "elimination" is to reduce and homogenize residual stress, which is not strictly eliminated. Vibratory stress relief (VSR) is becoming more and more popular because of its advantages of low equipment investment, low energy consumption and quick effect. At present, vibration aging is widely used in the field of ferrous metals [6, 7], such as the vibration aging treatment of iron castings and carbon steel weldments, with obvious effect. However, the application examples and literatures of applying vibratory stress relief to reduce and homogenize the residual stress of non-ferrous metal components are relatively rare [1]. With the wide application of non-ferrous metals, especially aluminum alloys in engineering, the research in this field has attracted more and more attention. This paper attempts to study the elimination of residual stress in aluminum alloy materials by vibration aging through the test of typical cross-section aluminum alloy specimens, so as to provide experimental basis for the application of vibration aging technology in the field of non-ferrous metals

1 experimental scheme design

the purpose of loading the specimen is to prefabricate the residual stress. Therefore, the size of load f depends on two factors: one is that f must yield the material, that is, the strain during loading should be greater than 3581 ×， Second, F should not be too large to avoid material damage. Of course, from the perspective of this experiment, the load should be increased as much as possible without damaging the material, so as to obtain a larger residual stress. In the test, WE-300 hydraulic universal testing machine is used to apply load to the test piece, and the stress point is at the midpoint of the test piece, so that the test piece is subject to pure bending deformation. During the loading process, Es-1 standard dynamometer is used to measure the size, and yjr-5 resistance strain gauge is used to monitor the strain at the patch point. Table 1 shows the loading test results of the specimen, and the strain in the table is the change value in the horizontal direction of the monitoring point at the midpoint of the specimen

1.3 testing residual stress

using the drilling method to measure the residual stress of aluminum alloy specimens is a relatively mature method [8, 9]. Its basic idea is to drill a small hole in the component with residual stress, so that the corresponding strain will be generated in the neighborhood of the hole due to partial stress release. Measure these strains, and the original stress at the borehole can be obtained after conversion. As the drilling method is a destructive measurement method, according to the requirements of the experiment, the residual stress values before and after the vibration of a certain point can be predicted, so that a comparison can be made. However, it is very difficult to measure the residual stress twice at the same point. Therefore, the following method can be used to solve this problem. As shown in Figure 3, if you want to measure the residual stress values before and after the vibration of point a, select point a 'and point a "at the left and right of the surface of the same cross-section of point a at a distance of 10mm respectively, In this way, the residual stress changes of point a can be judged by measuring the residual stress values of point a 'and point a "before and after vibration. The basis of this method is: first, we have measured the residual stress of the specimen before loading, and found that the residual stress values on its surface are roughly equal, which is similar to the uniform field; Second, the loading method is that the central part of the specimen is loaded, resulting in the bending deformation of the specimen. Therefore, the residual stress values after unloading at 3 points a, a ', a "on the top of the same transverse load plane at point a are roughly equal; Third, it conforms to the basic principle of drilling method

1.4 vibration aging treatment

vibration aging is to apply a certain time of excitation near the resonance frequency of the component or structure with an exciter to achieve the purpose of reducing and homogenizing the residual stress. For homogeneous beams, different support forms have different natural frequencies. In this experiment, a two end fixed mechanical model is used, and its first-order natural frequency can be obtained by the following formula:

from the above formula, the first-order natural frequency of the system after the two ends of the specimen are fixed can be obtained, which is about 436hz. During the test, the excitation frequency of the test should be obtained by the sweep frequency of the signal generator near 436hz, and the dynamic stress value should not be greater than one third of the yield limit of the material. The connection of the test instrument is shown in Figure 4. The time of excitation near the resonance point, such as in a moving car, is generally controlled at about 15min

2 test results and data processing

2.1 test 1

select three points on the 800mm long test piece, as shown in Figure 5. The results of residual stresses at points a, B and C3 measured before and after vibration are shown in Figure 7. It can be seen from the figure that the reduction of residual stress before and after vibration is obvious

2.2 test 2

select 5 points on another 800mm long test piece, as shown in Figure 6. The residual stress results along the principal stress direction of points a, B, C, D and E5 measured before and after vibration are shown in Figure 8

3 analysis and discussion

(2) in test 1, the range of residual stress before vibration is -7.2~34.2mpa, but after vibration it becomes -25.6~5.3mpa, and the range of residual stress after vibration is 25.4% lower than that before vibration. In test 2, the value range before vibration is -12.6~31.9mpa, and the value range after vibration is -16.0~11.0mpa. The value range of residual stress after vibration is 39.3% lower than that before vibration. From the above analysis, it can be seen that vibration aging homogenizes the residual stress of the specimen, and the effect is also obvious

4 conclusion

from the above test and the analysis of its correlation with people's life, it can be seen that the vibration aging treatment of aluminum alloy components can significantly reduce and homogenize the residual stress value, and then it can be inferred that it is feasible to apply the vibration aging technology to other colored metal components. Of course, in the practical application of this technology in engineering, we still need to further accumulate experience and reasonably select various parameters

Gao faxing, pan Haihua, Shen Weifeng, Jiang Yiping, Wang Xuhua also participated in the experimental work of this paper

references

[1] Liu Yong, Xie Liewei, Wang liexin A summary of the effect of vibratory stress relief on residual stress Journal of Zhejiang University of technology, to be published

[2] an Zhengzhi The influence of residual stress on material properties Proceedings of the 6th National residual stress conference, 1998

[3] Li sunlight can drive this kind of graphene material to move u Yong, et al Residual Stresses Analysis for Actual Material Model of Autofrettaged Tube by nonlinear BEM，Int，essure Vessels Pinping，1991，48(9)：.

[4] Liu Xiang Mechanical and physical properties of cast alloys China Machine Press, 1982

[5] Wang Xingxin, Zhuang biaozhong Vibration eliminates stress Vibration and shock, 1983 (2):

[6] Dawson bratory Stress Relief：A Fundamental Study of Its Effectiveness．Journal Of Engineering Materials &．Technology，1980，102：.

[7] Li Hongsheng et al The effect of vibratory stress relief on the materials of welded components Journal of Dalian Institute of technology, 1987, 21 (3)

[8] migumeo Generation and Countermeasures of residual stress China Machine Press, 1983

[9] yuan Farong, Wu Shangli The residual stress test first checks whether there is resonance and calculation around the experimental machine Hunan University Press, 1987

[10] translated by Gu Weiming Standard method for determining residual stress by borehole strain measurement Mechanical strength, 1986 (end)

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