| 摘要: | 超音波震盪處理應用於鋁合金氧化膜診斷是一種新的發現及技術，其原理主要源自於液體中音波空泡的生成，成長及爆破。為釐清此種診斷技術的物理機制，以確切掌控此種技術診斷鋁合金氧化膜的可行性。本研究分為三部分加以探討，包括音波空泡在液體中生成與破壞行為的探討，以及應用於鋁及Al-XSi合金氧化膜診斷上的研究等。第一部分為音波空泡爆破衝擊的破損圖案及應變能分析，藉以瞭解音波空泡的生成，爆破，及其對鋁箔的破壞圖案及應變能。第二部分為音波空泡破壞在鋁氧化膜診斷上的基礎研究，除瞭解音波空泡群在氧化膜上生成的原因，並釐清氧化膜受到微小噴射水滴衝擊破壞而在拋光試片上顯現霧狀痕跡的過程。第三部分為音波空泡破壞在Al-XSi合金氧化膜診斷上的研究，藉以瞭解在氧化膜上各不同相間受到微小噴射水滴衝擊的破壞模式，以及不同組成Al-XSi合金其音波空泡沖蝕破壞表面的差異。以下針對各研究主題摘要說明如下： 第一部分：本研究主要探討超音波震盪處理過程中音波空泡的效應，超音波空泡強度藉由鋁箔在各種液體中震盪後表面所生成的破損圖案加以調查。這個破損圖案肇因於微小噴射液滴及伴隨產生的衝擊波撞擊所致。微小噴射液滴具有高速的衝擊壓力，主要源自於超音波空泡爆破時產生。超音波空泡的強度與液體的物理化學性質及超音波特性有關，諸如液體的密度及黏滯性，超音波的頻率及音速等。本研究中除討論這些因素對超音波空泡強度的影響外，同時對於微小噴射液滴具有的動能及鋁箔局部破損的應變能加以計算及比較。 第二部分：本研究為音波空泡破壞診斷氧化膜的基礎研究。鋁合金鑄件在熔解及澆鑄過程中甚為容易形成氧化膜，存在於鋁合金鑄件中的氧化膜有原始氧化膜或二次氧化膜兩種。前者是本來即存在於鋁合金鑄件中，而且經歷一段很長的時間；而後者是在鋁液充填過程中不安定的表面捲入氧氣而生成的氧化膜。氧化膜富含氧成分而難以光學顯微鏡觀察到，本研究提出一個簡單而強力的方法用來診斷氧化膜在鋁鑄件中的形狀及分布情形。在超音波震盪處理時，音波空泡在液體內成核，成長及爆破，並生成為小噴射液滴衝擊在試片表面上。眾多的微小噴射水滴衝擊在氧化膜上導致微裂縫的生成。微裂縫成長並逐漸連結在一起，終導致氧化膜的破壞。微小的氧化物顆粒自氧化膜處剝離下來，最後試片顯現沖蝕的表面，此沖蝕的表面在肉眼或光學設備的觀察下顯現霧狀痕跡。本研究利用試片在水中震盪過程的一系列照片及示意圖用以描述氧化膜在鋁試片表面上受到音波空泡沖蝕破壞的過程。除此以外，此方法亦應用於鋁及鎂合金氧化膜的診斷上，包含鑄錠，鑄件或鍛造品等。 第三部分：本研究提出超音波震盪方法用以診斷Al-XSi合金之氧化膜。鋁合金試片在超音波震盪處理期間，試片表面之氧化膜承受來自於音波空泡爆破的衝擊力作用而發生破壞，接著氧化物顆粒自氧化膜處剝離下來，部分拋光面顯現出受到沖蝕的表面。這些受到音波空泡沖蝕的表面反射光線而形成可見的霧狀痕跡，包含點狀，塊狀，片狀及條狀等幾種不同形狀。本研究主要利用超音波震盪處理以診斷純鋁及Al-XSi 合金之氧化膜，對於氧化物顆粒在超音波震盪處理後自氧化膜處剝離而產生不同沖蝕表面的過程加以討論。氧化膜承受微小噴射液滴衝擊而發生破裂，其破裂表面形態利用掃描式電子顯微鏡加以觀察及比較。另外配合電子微探儀分析其組成，藉以確認氧化膜存在並釐清其破壞機制。 An ultrasonic-vibration treatment is a new technique that can be used to diagnose oxide films on an aluminum alloy matrix. This technique combined with SEM observations can offer information about the shape and distribution of oxide films on aluminum alloys. The key principle of the method is dependent on the nucleation, the growth and collapse of acoustic cavitation bubbles in the liquid. This method has been proven to be applicable to the diagnosis of oxide films that form on aluminum alloys. The study can be divided into three main areas: acoustic cavitation damage behaviors; a fundamental study of the diagnosis of oxide films on aluminum castings; and an applied study on the diagnosis of oxide films due to cavitation damage on Al-XSi alloys. The study on damage patterns and strain energy produced by the impact of collapsed acoustic cavitation can helped us to realize the damaging behavior of acoustic cavitation bubbles that collapse near/on the Al-foil surface, and strain energy produced from micro-jet impacts on the Al-foil. The study on the diagnosis of oxide films by cavitation micro-jet impact not only helped to understand the behavior of acoustic cavitation that occurs near/or on the oxide film surface, but also shows how water micro-jet impacts can cause fractures in the oxide film, which erodes the surface of the treated sample. This eroded surface will show as a foggy mark in visual or optical observations. The study on the diagnosis of oxide films in Al-XSi alloys by cavitation damage helped us visualize fractured surface morphologies of an eroded surface and variations in the oxide films difference in varies with the silicon content. The individual can be summarized as follows: Part 1: This study discusses the nucleation of cavitation bubbles during ultrasonic-vibration treatment. Different liquids were used to investigate the cavitation intensities of based on the damage marks displayed on aluminum foil samples. These damage marks resulted from the high impulsive pressure developed by micro-jet impacts associated with the action of shock waves. A micro-jet was initiated by the collapse of bubble clouds. The intensity of the cavitations depends on the physico-chemical properties and ultrasonic characteristics of the various liquids, such as the density and viscosity, the ultrasound frequencies and the traveling velocity. The effects of these factors on the intensity of the cavitation bubbles are discussed and the kinetic energies of the micro-jet impacts, along with the strain energy of deformed aluminum foil, are calculated and compared. Part 2: This is a fundamental study on the diagnosis of oxide films caused by cavitation damage. Oxide films form readily when aluminum alloy castings are melted and/or poured. There are both primary and secondary types of oxide films. The former is inherited from the ingot and has been known to exist in aluminum alloy casting for a long period of time. During the filling of the mold cavity, the free unstable surface of the molten metal causes a secondary oxide film to form on the aluminum alloy castings. These oxide films are usually rich in oxygen, but are difficult to observe by optical microscope. This paper presents a simple but powerful method for observing the shape and size of oxide films on the aluminum matrix. During an ultrasonic-vibration treatment, cavitation bubbles could nucleate, grow and collapse, generating micro-jets on the surface of sample. These water micro-jets then had an impact on the oxide film initiating micro-cracks. The cracks grew or became linked together, which caused fractures in the oxide film. Tiny oxide particles became detached from the oxide film to erode the surface of the treated sample. This eroded surface would show as a foggy mark in visual or optical observations. A series of photographs were made and are shown to illustrate the cavitation erosion process of oxide film on the surface of an aluminum sample. In addition, the presented method is shown to be useful in the diagnosis of oxide films that form on aluminum and magnesium alloys, including in ingots, castings or wrought products. Part 3: In this study we propose an ultrasonic-vibration method for the diagnosis of oxide films entrapped in Al-XSi alloys. These oxide film fractured and particles became detached from oxide film during the ultrasonic-vibration treatment. The polished surface became partly eroded after ultrasonic-vibration treatment. The eroded area was reflected as differently shaped visible foggy marks, including lumps, flakes, strips or spots. This paper presents summarized sequential illustration of the formation of eroded areas, and foggy marks on pure aluminum and Al-XSi alloys during ultrasonic-vibration treatment. In order to confirm that oxide films truly existed on the aluminum matrix, and to realize the mechanism where by oxide particles became detached from oxide films during ultrasonic-vibration treatment, the morphologies of fractured surface were observed by using scanning electronic microscopy (SEM), and the constituents of the oxide films were also analyzed by electron probe microanalysis (EPMA). For various types of Al-XSi alloys, the fractured surface morphologies of the oxide film were also compared and analyzed. |
