熱處理與稻殼燃燒灰質微粒添加對AA5052與AA6061鋁合金摩擦攪拌異質接合之效應研究

Abstract

本研究使用摩擦攪拌銲接製程應用於AA5052與AA6061鋁合金之異質對接，攪拌工具使用高速鋼材質，攪拌桿與機台主軸之傾斜角設定為2度，探討不同轉速與進給對銲件接合性質之影響。為了改善接合品質，本研究針對銲接件進行銲後熱處理，並於攪拌區加入稻殼燃燒灰質微粒，再針對接合成功之銲接件進行顯微組織與機械性質分析。 實驗結果顯示，在接合攪拌區兩種合金產生混合效果，達到有效接合，並有晶粒細化現象，而在熱影響區則發生晶粒粗大化。硬度量測結果發現銲道整體硬度低於原始母材，且在AA6061熱影響區之硬度最低，約為50 Hv，拉伸試驗之試片均於此處斷裂。當主軸轉速為1600 rpm、進給速度為40 mm/min時，可以獲得較佳之機械性質，抗拉強度為172.7 MPa，最大延伸率為10.3%。為提升銲接件之機械性質，本研究分別於銲後實施160℃持溫12小時之T5熱處理與530℃持溫1.5小時後再進行160℃持溫12小時之T6熱處理，硬度分析結果顯示T5熱處理可以提升AA6061側攪拌區之硬度達100 Hv左右，但對於熱影響區及AA5052側攪拌區之硬度則無明顯提升，銲接件之抗拉強度稍有提升，但延伸率略降，試片斷裂處仍在AA6061側之熱影響區。經T6熱處理後AA6061側攪拌區與熱影響區之硬度均提升至130 Hv左右，示差掃描熱分析(DSC)的結果顯示有析出物形成，拉伸試片的斷裂處則為銲道中央部位。另一方面，於攪拌區混入稻殼燃燒灰質微粒，分別經1~4次的摩擦攪拌製程，經T6熱處理後可以提升攪拌區的硬度，SEM/EBSD分析的結果顯示具有晶粒細化的效果，經混入稻殼燃燒灰質微粒後重複攪拌2~4次的試片，拉伸後於AA5052側斷裂，抗拉強度最高可以提升到211 MPa，延伸率則提升至12.6%左右。

This research is devoted to using the friction stir welding process for the butt joint of AA5052 and AA6061 aluminum alloy. For the stir tools, high-speed steel is selected, and the inclination angle between the stir rod and the main spindle of the machine is set to 2 degrees. Thereby, this study explored the effects of different speeds and feeding on the joint properties of weldments. Based on the goal of improving joint quality, this research performed post-weld heat treatment for welded specimens, and added rice husk burning ash particles in the stir zone, and then conducted correlation analysis of the microstructure and mechanical properties of the welded specimens that were successfully joined. It can be understood from the experimental results that the two alloys in the joining and stirring zone produce a mixed effect, thereby achieving effective joining, and there is a phenomenon of grain refinement. As for the heat-affected zone, the phenomenon of grain coarsening occurs. Based on the hardness measurement results, the author found that the overall hardness of the weld bead is lower than the original parent material. Moreover, the hardness in the heat-affected zone of AA6061 is the lowest, about 50 Hv, and the test pieces that have undergone the tensile test are all broken here. When the spindle speed is 1600 rpm and the feed rate is 40 mm/min, better mechanical properties can be obtained. Continuing the above, the tensile strength is 172.7 MPa and the maximum elongation is 10.3%. Due to the need to improve the mechanical properties of the welded parts, this study performed T5 heat treatment at 160℃ for 12 hours after welding, and T6 heat treatment at 160℃ for 12 hours at 530℃ for 1.5 hours. Then, the hardness analysis results show that T5 heat treatment can increase the hardness of the stirring zone on the AA6061 side by about 100 Hv. However, this process does not significantly improve the hardness of the heat-affected zone and the stirring zone on the AA5052 side. The tensile strength of the welded parts is slightly improved, but the elongation is slightly reduced. The fracture of the test specimens in this process is still in the heat-affected zone on the AA6061 side. Furthermore, after T6 heat treatment, the hardness of the stirring zone and the heat-affected zone on the AA6061 side both increase to about 130 Hv, and the formation of precipitates is found by differential scanning calorimetry (DSC) analysis. As for the fracture location of the tensile test specimens, it is the center of the weld bead. On the other hand, after mixing rice husk burning ash particles in the mixing zone, it is subjected to 1 to 4 friction stir welding processes and T6 heat treatment to increase the hardness of the stiring zone. The results of SEM/EBSD analysis showed that the effect of grain refinement appeared. The test specimens mixed with rice husk burning ash particles and repeated stirring 2 to 4 times broke on the AA5052 side after tensile testing, the tensile strength can be increased to 211 MPa, and the elongation is improved to about 12.6%.