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A Study on the Joining Properties of Al-Cu Alloys by Friction Stir Welding
C. P. Cheng
C. H. Tien
friction stir welding
Al-Cu系合金為高強度熱處理型鋁合金，由於具有低密度、高比強度之特性，是一種理想的航太結構材料。摩擦攪拌銲接(friction stir welding, FSW)是一種新式固態接合銲接法，可避免鋁合金材料在熔融銲接法(fusion welding)中所產生的偏析、熱裂、氣孔及噴濺等現象，而造成機械性質劣化的缺點。本研究選用Al-Cu系2091-T3合金和2024-T651合金作為實驗材料，進行個別單一合金及2091-T3與2024-T651異質鋁合金的FSW接合，經由銲後、自然時效30天和人工時效170°C-8hr等三種時效處理條件，透過微觀組織觀察、硬度試驗、拉伸試驗和SEM分析，來了解微觀組織變化及機械性質間的關係。
Abstract Among all heat treatment type aluminum alloys, Al-Cu series alloys have been recognized by its high strength, low density and high specific modulus properties. This significant advantage makes it the perfect structural material for aerospace applications. Friction stir welding (FSW) is a unique solid-state joining process that can prevent material from mechanical properties degradation which is caused by segregate, hot cracking, porosity and spatter in fusion welding during the process. The 2091-T3 and 2024-T651 were selected from Al-Cu series alloys for this study. Individual alloy FSW joint processes were performed for 2091-T3 and 2024-T651 and bi-alloy FSWs for 2091-T3/2024-T651 were made before other steps. After the welding, The aging treatment of the specimens were performed under the condition of naturally (open-air) aged for 30 days and artificially aged under 170°C for 8 hours. After these three types of aging treatment, the microstructures changes and reactions among mechanical properties were examined through the microstructures observations, hardness testing, and tensile test as well as SEM analysis. The welding path obviously exhibited three microstructural sections through FSW joint. The stir zone (SZ) characteristically exhibited a refined equiaxed grain structure, the thermomechanically affected zone (TMAZ) demonstrated macroscopic deformation and grain growth, beyond the TMAZ a heat affected zone (HAZ) where changes were similar to parent metal (PM) with grain organization. 2091-T3 alloy has the highest joint strength of the artificial aging after FSW joint. 2024-T651 alloy showed highest joint strength of the natural aging after FSW joint, but it still lower than the strength of parent metal. The bi-alloys 2091-T3/2024-T651 presented a great joint strength with counterclockwise rotation after FSW joint, investigated by aging treatments with the cylindrical tool in both clockwise and counterclockwise directions.
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