2014铝合金薄板搅拌摩擦焊工艺研究

发布时间：2018-04-26 12:18

本文选题：薄板 + 搅拌摩擦焊　；参考：《江苏科技大学》2017年硕士论文

【摘要】：2014铝合金被广泛应用于航空、能源、交通等行业,其强度高,热强性好,但是焊接性能较差。常规方法焊接时容易出现裂纹、气孔等问题。且焊件较薄时,变形大、难矫正等问题也很难解决。本文针对薄板铝合金焊接的特点,对1mm厚铝合金薄板进行了高转速焊接工艺探索、特征参数的采集和分析,同时进行了数值模拟的验证及焊缝的性能测试。工艺试验结果表明:超高转速的搅拌摩擦焊工艺,采用微型搅拌头即可以实现对铝合金薄板的焊接。工艺试验范围为转速:10000rpm~16500rpm,焊接速度:50mm/min~170mm/min。当转速小于15000rpm,下压量很难控制,焊接效率低且表面成形差焊后变形严重。当转速达到15000rpm,焊接所需的下压量极小,减薄程度小,且整个过程易于控制。在空气中冷却,变形不可避免,而辅助水雾冷却可以得到表面成形好且无变形的焊件。轴向力的检测分析结果表明:转速在10000rpm到16500rpm范围内,焊接阶段的轴向力均低于200N,这有利于实现轻量化的搅拌摩擦焊接过程,改进了传统搅拌摩擦焊对机身承载要求高的缺点,进一步降低了成本。轴向力的变化规律与传统搅拌摩擦焊相似,在下压过程中,轴向力先增大后减小,焊接开始后逐渐趋于平稳。搅拌头旋转速度越高,轴向力峰值越小。此外,轴向力稳定是接头纵向性能均匀的保证,同时,水冷对轴向力也起着重要作用,因为水冷可以减少热量聚积,防止轴向力的突变。焊缝性能分析测试结果表明:焊接接头宏观形貌存在明显的焊核区、热机械影响区和母材区,热影响区则不明显。母材晶粒沿着轧制方向拉长。焊核区在搅拌作用下发生了动态的回复再结晶,晶粒细小且沉淀相发生了重溶。热机械影响区的晶粒发生了变形且在后退侧更明显。拉伸结果显示,在固定的转速下,焊缝的力学性能随着焊速的增加先提高后降低。随着转速的提高,焊缝抗拉强度的峰值先增大后减小;转速的提高带来了延伸率的提高。转速为16000rpm焊速为110mm/min时强度最高,约为母材的75%。焊缝强度较低时,断口一般在焊缝中心,焊缝强度较高时,断口在前进侧或后退侧搅拌区与母材的交界处。断口在中心,断口形貌为韧脆混合型断裂,断口在交界处,断口形貌呈韧性断裂特性。焊缝硬度的测试结果显示,硬度分布没有明显的“W”形。焊缝的耐腐蚀性能研究结果表明,高转速搅拌摩擦焊后铝合金的耐蚀性稍有降低,腐蚀电位下降,腐蚀电流升高,电化学阻抗谱由高频感抗弧和低频容抗弧组成。搅拌摩擦焊焊接数值模拟的结果表明:轴向力p200N,转速W15000rpm的工艺条件,焊缝金属达到可焊接温度。轴向力极小的搅拌摩擦焊过程同样能够产生足够的热量和搅拌作用,但是同时也会引起变形。水雾冷却的方法可以加速焊缝散热使变形程度降低,是高转速搅拌摩擦焊的必要条件。温度场模拟验证了工艺的可行性,与实测结果基本一致。
[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.
【学位授予单位】：江苏科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.14

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