| 摘要: | 鋁合金因其重量輕、強度高與耐腐蝕，故廣泛的應用於工業界，材料在經過熱處理後，合金元素會在材料內部形成微顆粒，這些微顆粒會影響到材料的機械性質。因此，本研究的目標是建立以非破壞性檢測方式評估材料內部微顆粒的分佈。 在超音波探頭的選用上，低頻（5 MHz、10 MHz）的探頭適用於量測材料的晶界與晶粒尺寸，而高頻（20 MHz）的探頭則是用於量測微顆粒的分佈。在使用浸液式超音波檢測時，探頭與受測物間的距離在使用近場長度時可以降低誤差的產生，提高量測值的準確度。 使用頻率為5 MHz的探頭時，衰減率與內耗能的主要影響因素為材料內較巨觀的結構（晶界、差排密度與晶界上的微顆粒）。結合 R_L(單位面積上晶界長度)與 Q^(-1)(內耗能)間的關係，可以利用內耗能的變化來推測材料內部巨觀結構。超音波雜訊的振幅變化主要是由材料內部晶粒尺寸分佈不均勻所造成，而不是晶粒尺寸的大小。 本實驗使用超音波檢測法（Ultrasonic testing）量測7xxx 系鋁合金材料的超音波衰減率。討論材料內部微顆粒、基地、晶界與材料熱處理後微顆粒所產生的應力場對超音波衰減率的影響（∑▒〖f_pi A_i 、〖B_m 、α〗_GB 與〖 C〗_(σ_p ) 〗）。使用光學顯微鏡（Optical Microscope, OM）量測不同尺寸範圍的微顆粒數量，將微顆粒對衰減率的影響區分為 5～10 μm、10～20 μm、20～40 μm 與40～50 μm 分別佔材料的體積分率（f_p1、f_p2、f_p3 與 f_p4）對超音波衰減率的影響。結合超音波檢測得到的內耗能與渦電流檢測法（Eddy current testing）得到的導電度可以推算出材料內部微顆粒的分佈。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. |
