臺灣博碩士論文加值系統

本研究探討AA 7075-T6鋁合金及經微粒子珠擊試件評估後續鍍硬鉻以及硬質陽極處理對其機械性質的影響。實驗內容包括:研究使用SEM觀察珠擊後塑性變形的表面形貌、鍍硬鉻和硬陽層的組織便用EBSD分析珠擊層晶粒尺寸變化並進行應變量分析；研究使用TEM進一步確認細晶組織的形貌和尺寸；並以微小維克氏硬度機及奈米壓痕試驗機進行硬度量測。白光干涉儀量測珠擊前後粗糙度的差異，實驗藉由XRD量測珠擊過後試片表面的殘留應力，並且進行旋轉疲勞試驗測試不同條件下試棒的疲勞強度，最後進行破斷面觀察及探討破損原因。
實驗結果顯示:AA 7075-T6鋁合金經過珠擊後表面產生巨大殘留壓應力，並且伴隨晶粒細化的現象，不僅表面硬度提升且疲勞強度也大幅的升高。珠擊表層和鍍硬鉻層間有良好的結合性，即使鍍鉻層有著許多垂直裂紋，疲勞裂紋的生長也會受到珠擊層的有效阻擋，珠擊後鍍硬鉻試件兼具高表面硬度抗磨耗能力及高疲勞強度。然而珠擊後再經過硬陽處理，陽極氧化層會侵蝕珠擊表層，表層殘留應力降低而影響其疲勞強度，但仍具和未陽極處理試件相當之疲勞強度。而未珠擊之7075-T6試件經硬陽處理後，其疲勞強度大幅降低。

In this study, the effects of micro-shot peening on the rotating bending fatigue resistance of Cr-electroplated and hard anodized AA 7075-T6 alloy were evaluated. The surface morphology of bombarded dents as well as the microstructure of the Cr-plated and anodized samples were examined by using SEM. EBSD was applied to determine the grain size of the shot-peened layer and change in strain within the peened depth. The detailed microstructure of the shot-peened layer was inspected by TEM. Micro Vickers and nanoindenter were used for hardness measurement in different zones of the shot-peened sample. Surface roughness of the tested sample with or without shot peening was inspected by white light interferometer. The change in residual stress with the depth of the shot-peened sample was determined by XRD. Rotating bending fatigue was performed to determine the fatigue strength/life of the tested sample.
The experimental results show that shot-peening introduced high residual stress into AA 7075-T6 aluminum alloy and caused a significant grain refinement within the shot-peened layer. The bombarded surface of the shot-peened sample showed a noticed strain-hardening, resulting in a great increase in hardness. Hard-Cr layer consisted of numerous fine cracks aligned in the direction normal to the external surface. Without the need of crack initiation, the Cr-plated sample showed a much lower fatigue strength/life than the un-plated one. With the introduced compressive residual stress in the shot-peened layer, the growth of fatigue cracks will be effectively retarded. The results indicated that the hard anodizing would sacrifice or damage the shot peened layer, thus, the residual stress of the shot-peened layer will be reduced. Such event caused a decrease in fatigue strength, However, the shot-peened anodized sample still had the similar fatigue strength to that of the original substrate. Without shot-peening, hard anodizing led to a significant decrease in fatigue strength of 7075-T6 alloy.

摘要 I
Abstract II
第一章 前言 1
第二章 文獻回顧 2
2-1 鋁合金簡介 2
2-1-1 鋁合金種類介紹 2
2-1-2 熱處理對鋁合金性能之影響 4
2-1-3 7075 疲勞性質 5
2-2 鍍硬鉻簡介 5
2-2-1 鍍硬鉻製程 6
2-2-2 鍍硬鉻對疲勞性質之影響 7
2-3 硬質陽極簡介 7
2-3-1 硬質陽極製程 8
2-3-2 硬質陽極對疲勞性質之影響 10
2-4 微粒子珠擊法簡介 10
2-4-1 微粒子珠擊法對材料之機械性質影響 10
第三章 實驗流程與方法 26
3-1 實驗材料 26
3-2 實驗流程 26
3-3 拉伸試驗 26
3-4 旋轉疲勞試驗 27
3-5 金相顯微組織觀察(OM、SEM) 27
3-6 奈米壓痕量測(Nanoindenter) 27
3-7 微小維克式硬度機量測(Vickers hardness tester) 28
3-8 表面粗糙度量測(White Light Interferometer) 28
3-9 電子背向散射繞射(EBSD)分析 28
3-10 穿透式電子顯微鏡(TEM)觀察 29
3-11 殘留應力量測 29
第四章 結果與討論 44
4-1 拉伸試驗 44
4-2旋轉疲勞試驗 45
4-3顯微組織觀察 47
4-4 奈米壓痕量測(Nanoindenter) 48
4-5 微小維克式硬度機量測(Vickers hardness tester) 48
4-6 表面粗糙度量測(White Light Interferometer) 48
4-7 電子背向散射繞射(EBSD)分析 49
4-8 穿透式電子顯微鏡(TEM)觀察 50
4-9 殘留應力量測 50
第五章 結論 77
第六章 參考文獻 78

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