研究生: |
劉如真 Ju-Jen Liu |
---|---|
論文名稱: |
鋁合金A6061-T6摩擦攪拌點銲接合機構之研究 A study of joining mechanism on Al Alloy A6061-T6 Friction Stir Spot Welds |
指導教授: |
林原慶
Yuan-Ching Lin |
口試委員: |
雷添壽
Tien-Shou Lei 向四海 Su - Hai Hsiang 鄭偉鈞 Wei-Chun Cheng 鄭慶民 Ching-Min Cheng 蘇程裕 Cherng-Yuh Su |
學位類別: |
博士 Doctor |
系所名稱: |
工程學院 - 機械工程系 Department of Mechanical Engineering |
論文出版年: | 2012 |
畢業學年度: | 100 |
語文別: | 中文 |
論文頁數: | 155 |
中文關鍵詞: | 摩擦攪拌點銲 、材料流動 、孔隙效應 、攪拌工具形貌 、拉剪破壞強度 |
外文關鍵詞: | FSSW, Materials flow, Void effect, Tool geometry, Tensile shear failure load |
相關次數: | 點閱:242 下載:6 |
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摩擦攪拌點銲(FSSW)為摩擦攪拌銲接(FSW)的擴充應用,其為一固態接合技術,由於過程中溫度未達熔點,故無氣孔、凝固裂紋等傳統熔融銲接所產生之缺陷,所以特別適合鎂、鋁合金等輕金屬點銲的應用。
實驗結果發現暫態拘束空間(Constraint space)之建立,為形成攪拌區及銲件接合行為的必要條件。摩擦攪拌點銲期間,除工具的攪拌作用(Traction force)直接造成材料的塑性流動外,由於攪拌工具幾何形狀在拘束空間內造成的壓力梯度(孔隙效應)更是引發材料軸向或徑向流動及形成攪拌區的關鍵因素,而攪拌區的形成及成長將影響板材的接合行為及上板材厚度減少的趨勢,進而影響銲件之機械性質。因此適當的攪拌工具設計將可大大提升銲件的接合效能。而適當的製程參數也是形成良好銲件的必要條件。三角柱凸銷及螺紋圓柱凸銷以不同的塑性流動機制形成攪拌區,螺紋圓柱凸銷驅動材料軸向流動的效應高於光滑三角柱凸銷;但三角柱的凸銷其驅動材料徑向(Radial direction)流動的效應,則高於螺紋圓柱凸銷。因此兩者的銲件具有十分不同的銲道形貌。由於Hook幾何形狀的差異,其拉剪破壞模式及強度也明顯不同。螺紋圓柱凸銷製程之銲件其拉剪強度略高於三角柱製程之銲件。
本文建立不同幾何形狀的工具之摩擦攪拌點銲(FSSW)材料流動的模式,並藉由追蹤物(tracer)技術及實驗觀察來闡述攪拌工具的肩部及凸銷之幾何形狀對材料塑性流動及板材接合的效應,並提出攪拌區(SZ)形成機制,以及銲接參數對銲件破壞模式及接合強度之效應的論述,期能對FSSW的工具設計提供參考。
Friction stir spot welding (FSSW) is a derivative process of the friction stir welding (FSW), which is a solid-state joining technique, due to the process temperature below the melting point, so it therefore does not exit porosity, solidification cracking and other defects generated by traditional fusion welding. It is especially suitable for magnesium, aluminum and other light metal alloys.
Results showed that, the construction of the transient constrained space is a prerequisite to the formation of a stirring area and the bonding of the welding work pieces. Friction stir spot welding (FSSW) is driven mainly by the materials flow induced by the stirring tool in a constrained space that gradually diminishes the contact interface between the upper and lower plates leaving them bonded to each other. The stirring tool has a decisive influence on the flowing behavior of the plastic and the bonding strength of the welding work pieces.
During the FSSW period, except for the traction force of the tool that can directly cause the flow of plastic materials, the pressure gradient generated in the constrained space by the tool geometry that causes the axial or radial flow of the materials and the formation of a stir zone are even more key factors. The formation and growth of the stir zone will influence the bonding behavior of the plates and the effective thickness reduction trend of the upper plate. This will further influence the mechanical strength of the welding work pieces. Therefore, the appropriate design of the stirring tool can greatly improve the bonding performance of the welding work pieces. In addition, appropriate process parameters are also a prerequisite to the formation of well-welded work pieces.
The triangular tool pin and the threaded cylindrical tool pin will form stir zone caused by the different plastic flow mechanisms. The threaded cylindrical tool pin has a higher performance than the smooth triangular tool pin when driving the axial flow of materials. However, the triangular tool pin has a higher performance than the threaded cylindrical tool pin when driving the radial flow. Therefore, the nuggets of welding working pieces of the two types are totally different in their geometric features. Because of the geometrical differences of the hook, its tensile shear failure modes and strength also have significant differences. The welding work pieces made by the process using the threaded cylindrical tool pin has a slightly higher tensile and shear strengths than those made by the process using the triangular tool pin.
This study established the FSSW materials flow modes using different geometrical tools as well as observations from the experiments. It has also used tracer techniques to elaborate on the influences on the flow of materials and the bonding effect of the plates induced by the shoulder of the stirring tool and the geometrical shapes of the tool pin. The formation mechanism of the stirring zone was presented and the effects of the welding parameters on the welding work piece failure modes and their bonding strength were also discussed. This was done in the hope of providing more useful references for the FSSW tool design.
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