Research On Mechanical Effects And Strengthening Mechanism Of 2A02 Alloy By Cavitation Bubbles Induced By Laser Processing

The cavitation refers to a kind of fluid movement which exists in the water conservancy machinery commonly. When local pressure inside liquid decreases, the development and collapse of interface on steam or gas hole of the liquid and liquid solid interface formation. If the cavity near the solid wall, the wall effect will occur. The microjet and shockwave phenomenon appear in the process of bubble collapse.Meanwhile, with the development of science and technology, the laser processing technology has been the promotion and application of various fields. This paper proposed the laser strengthen technology of the target in the water environment called Laser Cavitation Enhancement. With the cavitation bubbles generated by laser has the advantages of good spherical symmetry, easy control and no mechanical deformation, it has become an important tool to study cavitation. In order to improve the strength of the material and prolong its service life, this paper makes a theoretical and experimental study on the laser cavitation enhancement technology. The main contents and achievements are as follows:(1) Studied on the underwater target mechanical effect by pulse laser. Analyzed the formation and development mechanism of plasma shockwaves induced by underwater laser on the basis of comparing the traditional laser shock processing technology.Theoretical study on the dynamics of underwater laser cavitation bubbles are as follows:the formation process of underwater laser cavitation bubbles, pulsation characteristics,as well as the motion equation, etc.. Studied the basic theory of the dynamics of laser cavitation bubbles near the wall, taking the 2A02 alloy as the research object, mainly including the pulsation characteristics of the laser cavitation bubbles near the wall, as well as the shockwave and microjet of laser-induced cavitation bubble near the wall.(2) Setted up the experimental platform, studied the acoustic signal and corresponding target mechanical effect by the pulsed laser with piezoelectric sensor under water. Compared and discussed the intensity of laser generated acoustic signalabout underwater target by different pulse incident direction, as well as surface topography, and then adopted reasonable laser incident direction. Finally, obtained a qualitative effect on the target surface of the shock pressure according to the formula conversion relationship between sound pressure signal and mechanical effect. And then compared with the target yield strength, obtained that the target plastic deformation and residual compressive stress has occurred, so the rationality and effectiveness of the technology are verified.(3) Analyzed the mechanical properties of the target of laser cavitation after the test,including its residual stress, surface hardness, surface roughness, surface morphology,etc.. And also discussed the case of different laser energy and ‘H’, the variable trend of the parameters in the corresponding target before and after enhancement. Summarized and analyzed the strengthen law finally.