本文選題：薄板 + 攪拌摩擦焊��； 參考：《江蘇科技大學》2017年碩士論文

【摘要】：2014鋁合金被廣泛應用于航空、能源、交通等行業(yè),其強度高,熱強性好,但是焊接性能較差。常規(guī)方法焊接時容易出現裂紋、氣孔等問題。且焊件較薄時,變形大、難矯正等問題也很難解決。本文針對薄板鋁合金焊接的特點,對1mm厚鋁合金薄板進行了高轉速焊接工藝探索、特征參數的采集和分析,同時進行了數值模擬的驗證及焊縫的性能測試。工藝試驗結果表明:超高轉速的攪拌摩擦焊工藝,采用微型攪拌頭即可以實現對鋁合金薄板的焊接。工藝試驗范圍為轉速:10000rpm~16500rpm,焊接速度:50mm/min~170mm/min。當轉速小于15000rpm,下壓量很難控制,焊接效率低且表面成形差焊后變形嚴重。當轉速達到15000rpm,焊接所需的下壓量極小,減薄程度小,且整個過程易于控制。在空氣中冷卻,變形不可避免,而輔助水霧冷卻可以得到表面成形好且無變形的焊件。軸向力的檢測分析結果表明:轉速在10000rpm到16500rpm范圍內,焊接階段的軸向力均低于200N,這有利于實現輕量化的攪拌摩擦焊接過程,改進了傳統(tǒng)攪拌摩擦焊對機身承載要求高的缺點,進一步降低了成本。軸向力的變化規(guī)律與傳統(tǒng)攪拌摩擦焊相似,在下壓過程中,軸向力先增大后減小,焊接開始后逐漸趨于平穩(wěn)。攪拌頭旋轉速度越高,軸向力峰值越小。此外,軸向力穩(wěn)定是接頭縱向性能均勻的保證,同時,水冷對軸向力也起著重要作用,因為水冷可以減少熱量聚積,防止軸向力的突變。焊縫性能分析測試結果表明:焊接接頭宏觀形貌存在明顯的焊核區(qū)、熱機械影響區(qū)和母材區(qū),熱影響區(qū)則不明顯。母材晶粒沿著軋制方向拉長。焊核區(qū)在攪拌作用下發(fā)生了動態(tài)的回復再結晶,晶粒細小且沉淀相發(fā)生了重溶。熱機械影響區(qū)的晶粒發(fā)生了變形且在后退側更明顯。拉伸結果顯示,在固定的轉速下,焊縫的力學性能隨著焊速的增加先提高后降低。隨著轉速的提高,焊縫抗拉強度的峰值先增大后減小;轉速的提高帶來了延伸率的提高。轉速為16000rpm焊速為110mm/min時強度最高,約為母材的75%。焊縫強度較低時,斷口一般在焊縫中心,焊縫強度較高時,斷口在前進側或后退側攪拌區(qū)與母材的交界處。斷口在中心,斷口形貌為韌脆混合型斷裂,斷口在交界處,斷口形貌呈韌性斷裂特性。焊縫硬度的測試結果顯示,硬度分布沒有明顯的“W”形。焊縫的耐腐蝕性能研究結果表明,高轉速攪拌摩擦焊后鋁合金的耐蝕性稍有降低,腐蝕電位下降,腐蝕電流升高,電化學阻抗譜由高頻感抗弧和低頻容抗弧組成。攪拌摩擦焊焊接數值模擬的結果表明:軸向力p200N,轉速W15000rpm的工藝條件,焊縫金屬達到可焊接溫度。軸向力極小的攪拌摩擦焊過程同樣能夠產生足夠的熱量和攪拌作用,但是同時也會引起變形。水霧冷卻的方法可以加速焊縫散熱使變形程度降低,是高轉速攪拌摩擦焊的必要條件。溫度場模擬驗證了工藝的可行性,與實測結果基本一致。
[Abstract]:2014 aluminum alloy is widely used in aviation, energy, transportation and other industries. The conventional welding method is prone to crack, porosity and other problems. When the welder is thin, it is difficult to solve the problems such as large deformation and difficult to be corrected. In view of the characteristics of aluminum alloy welding of thin plate, this paper explores the welding technology of 1mm thick aluminum alloy sheet at high rotational speed, collects and analyzes the characteristic parameters, and carries out the verification of numerical simulation and the performance test of weld seam at the same time. The experimental results show that the welding of aluminum alloy sheet can be realized by using micro stir head in the process of friction stir welding with super high speed. The range of process test is as follows: rotating speed: 10000rpmct 16500rpm, welding speed: 50mm / min / min 170mm / min. When the rotational speed is less than 15000rpm, the lower pressure is difficult to control, the welding efficiency is low and the deformation of surface forming is serious. When the rotational speed reaches 15000rpm, the welding pressure is very small, the thinning degree is small, and the whole process is easy to control. When cooling in air, deformation is inevitable, and surface formed and deformable welds can be obtained by auxiliary water mist cooling. The results of axial force detection and analysis show that the axial force in the welding stage is lower than 200Nin the range of 10000rpm to 16500rpm, which is beneficial to the realization of lightweight friction stir welding process and improves the disadvantage of traditional friction stir welding which requires high load of fuselage. The cost has been further reduced. The variation law of axial force is similar to that of traditional friction stir welding. In the process of compression, the axial force first increases and then decreases, and then gradually becomes stable after the beginning of welding. The higher the rotating speed of the mixing head, the smaller the axial force peak value. In addition, axial force stability is the guarantee of uniform longitudinal performance of the joint, and water cooling plays an important role in axial force, because water cooling can reduce the heat accumulation and prevent the sudden change of axial force. The results of weld performance analysis show that there are obvious nugget zone, thermomechanical effect zone and base metal zone in the macroscopic morphology of welded joint, but the heat affected zone is not obvious. The base metal grain is elongated along the rolling direction. Dynamic recovery recrystallization occurs in the nugget zone under agitation, and the grain size is fine and the precipitation phase is redissolved. The grains in the thermomechanical affected zone are deformed and are more obvious in the receding side. The tensile results show that the mechanical properties of the weld increase first and then decrease with the increase of welding speed at a fixed rotational speed. With the increase of rotational speed, the peak value of tensile strength of weld first increases and then decreases, and the increase of rotational speed leads to the increase of elongation. When the speed of 16000rpm welding is 110mm/min, the strength is the highest, about 75% of base metal. When the weld strength is low, the fracture surface is usually in the center of the weld, and when the weld strength is high, the fracture surface is at the junction between the front side and the back side and the base metal. The fracture surface is in the center, and the fracture morphology is ductile and brittle, and the fracture surface is at the junction with ductile fracture. The hardness distribution of the weld shows no obvious "W" shape. The results showed that the corrosion resistance of aluminum alloy decreased slightly, the corrosion potential decreased, the corrosion current increased, and the electrochemical impedance spectrum was composed of high frequency inductive arc and low frequency capacitive impedance arc after high speed friction stir welding. The results of numerical simulation of friction stir welding show that the welding temperature can be reached under the technological conditions of axial force p200N and rotational speed W15000rpm. Friction stir welding with minimal axial force can also produce enough heat and stirring, but also cause deformation. The cooling method of water mist can accelerate the heat dissipation of weld and reduce the degree of deformation, which is a necessary condition for high speed friction stir welding. The simulation of temperature field verifies the feasibility of the process, which is basically consistent with the measured results.
【學位授予單位】：江蘇科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG457.14

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