Research On Near-surface Characteristics And Strengthening Effect By Laser Induced Cavitation In AZ31B Magnesium Alloy

Cavitation is a widespread phenomenon in the fluid,with micro jet and the effect of the shock wave mechanics,often cause serious damage to hydraulic mechanical damage is great,but control of the process of cavitation and mechanical effects which can realize material on the surface of the reinforcement,turn harm into treasure.Laser cavitation has the advantages of good symmetry,easy operation and strong stability.In this paper,through constructing the laser induced cavitation experiment platform,using high speed photography technology research of laser induced cavitation in a variety of characteristics and its influencing factors in the pulse of the wall,in-depth analysis of cavitation mechanism;Mechanical effect strengthening with laser induced AZ31 B magnesium alloy material,through the surface morphology,hardness and residual stress performance,strengthening effect in the characterization of the laser cavitation reinforcement technology to provide theoretical and experimental basis.The main research contents and conclusions are as follows:(1)According to the theory of cavitation dynamics analysis,the research of laser cavity is in an infinite domain and the near wall "primary-inflation-contraction" fluctuating rule and the mechanical effect of micro-jet and shockwave are produced during cavitation,providing theoretical basis for cavitation strengthening experiment.The experimental study obtains the transient characteristics of laser induced cavitation in horizontal single wall,vertical single wall,parallel double wall surface,vertical double-wall surface and u-shaped wall surface.The results show that the cavitation effect can be influenced by the fluctuation of the five near-wall surfaces and the different parameters and can generate wall effect.Due to the unbalance pressure of the solid-liquid interface,the cavitation in the vertical wall pulsation and the concentration less than 2 will produce the micro-jet during the cavitation.When the amount of defocus is different,the laser induced cavitation bubbles near the parallel wall surface and the u-shaped wall surface will occur and generate the micro-jet phenomenon.When the bubble pulsates over the u-shaped wall,the cavitation generates separation and polymerization.(2)Study the effects of laser energy and defocusing amount on the cavitation pulse characteristics on the horizontal single wall.The results show that the larger the laser energy is,the longer the cavity pulsation cycles and the larger the maximum radius of the cavitation.The influence of laser defocusing amount on the maximum expansion radius of cavitation bubbles is not significant.The defocusing amount is smaller,the effect of the wall on the cavitation is more obvious and the period is longer.(3)The effect of laser cavitation on the surface morphology,hardness and residual stress of AZ31 B magnesium alloy is analyzed by experimentally studying the strengthening effect of laser cavitation.Results show that the bigger the laser energy and when H = 1,the material surface is smooth,the hardness is higher,the residual compressive stress is higher,too.It shows that the surface modification technology of laser cavitation strengthening is feasible and practical.