Research On Influencing Factors On Nonlinear Ultrasonic And Application In Aluminum Alloy Damage

6082 aluminum alloy is a 6-series(Al-Mg-Si)aluminum alloy.It can be heat-treated and has medium strength,good weldability and corrosion resistance.It is widely used in transportation and structural engineering industries.The engineering structure will inevitably be damaged during the service process.It is very important to make the plan for the quantitative and positioning of the structural damage as early as possible to ensure the safety of the structure.Recent studies have shown that nonlinear ultrasonic technology is expected to be a reliable means of non-destructive testing.This paper systematically introduces the nonlinear ultrasonic detection principle of material damage.Taking the 6082 aluminum alloy as the research object,the non-defective factors that may be encountered in practical applications are mainly studied by using the self-built nonlinear ultrasonic detection system.The effects include propagation distance,stress,temperature,surface roughness,and second phase precipitates.In addition,samples with different plastic damage were prepared,and the linear ultrasonic parameters(sound velocity,sound attenuation)and nonlinear parameters of each sample were measured,and their sensitivity to plastic damage was analyzed and compared.The results show that the linear ultrasonic coefficient is not obvious during the plastic damage of 6082-T6 aluminum alloy.The relative change of sound velocity is about 5.7%,and the relative change of sound attenuation coefficient is about 5%.The nonlinear ultrasonic parameter changes obviously,and it shows a significant upward trend during the plastic damage process.The nonlinear ultrasonic coefficients of longitudinal wave and surface wave are increased by 2.17 times and 5.01 times,respectively,compared with the original sample.Therefore,it can be concluded that nonlinear ultrasound is more suitable for the evaluation of plastic damage of 6082 aluminum alloy than linear ultrasound.At the same time,for the plastic damage process,the XRD-WH method was used to estimate the dislocation density,and the microstructure evolution was analyzed.The relationship between the microstructure-non-linear ultrasonic coefficient and the macroscopic mechanical properties of the material was discussed.