| dc.description.abstract | Having the light weight, higher mechanical strength and corrosion resistance, aluminum alloys have been widely used in industry. The material after heat treatment, alloy elements will be formed of particles in the matrix. The mechanical properties of material were affected by particles distribution. Therefore, the objective of this study is to use NDT (non-destructive testing) methods to assess the micro-structural changes inside the material.
The selection of the ultrasonic probe, at low frequency (5 MHz and 10 MHz) for measuring the grain boundary of the material, at high frequency (20 MHz) is used to measure the particles distribution. Immersion ultrasonic testing, the distance between the probe and measured sample is equal to the length of the near-field can reduce the measurement error and, increasing the accuracy of the measured values.
Using a 5 MHz probe, the ultrasonic attenuation and internal friction was affected by the grain boundary, dislocation density, and grain boundary. Combine the relationship between R_L(the length of grain boundary per unit area) and Q^(-1)(internal frication), could predict macro-structure by the variation of internal friction.The amplitude variation of the ultrasonic noise was mainly due to non-uniform distribution of grain, not’’s grain size.
The study used UT (ultrasonic testing) to obtain the attenuation of 7000 series aluminum alloy. We measure attenuation and separate into four parts for discuss: i) particles distribution set as ∑▒〖f_pi A_i 〗 ; The influence of particles on ultrasonic attenuation were divided to varied size range (5～10 μm, 10～20 μm, 20～40 μm and 40～50 μm). The range of particles of 7000 series aluminum alloy was observed by using OM (Optical microscope). ii) matrix set as B_m value. iii) grain boundary scattering set as α_GB value. iv) the particles stress field by heat treatment set as 〖 C〗_(σ_p ) value. Finally, combine ultrasonic attenuation, internal friction, and conductivity to estimate micro-structure of the aluminum alloys.
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