异质航空铝合金FSW焊接接头的疲劳特性研究1）
2014-08-13 17:21:58
作者：本站整理来源：
马玉娥 *,2)，李 江*，赵振强*
*（西北工业大学航空学院，西安 710072）
*（西北工业大学航空学院，西安 710072）
摘要：2xxx系与7xxx系航空铝合金被认为采用传统焊接无法焊接的金属。因能焊接2xxx系与7xxx系铝合金，并且能减轻重量、提高综合性能和节省成本，搅拌摩擦焊（Friction Stir Welding-FSW）整体结构被认为是未来航空结构构型之一。针对异质2024T3和7075T6两种航空铝合金FSW焊接接头的残余应力分布、力学性能及疲劳裂纹扩展性能，本文进行了深入研究。首先采用适当的焊接参数焊接了2024&7075异质薄板。焊后采用X-射线衍射法对四种典型焊件进行了残余应力测试，得到了异质焊件内的残余应力分布。对于异质焊件，其内部残余应力分布无明显的双峰特征，焊缝两侧的残余应力分布并不对称。2024侧的残余应力值浮动较大，7075侧的残余应力值浮动较小，且主要为拉伸残余应力。然后根据相关标准，设计出两种不同的力学性能测试试验件，并对两种材料的异质接头进行了力学性能试验，得到了焊缝区域沿焊缝方向与垂直于焊缝方向材料的应力应变曲线，对比分析了断口形貌特征。异质接头焊缝区两个方向材料的应力应变性能介于两种同质焊缝材料之间，拉伸断口参差不齐，垂直焊缝方向试样断裂位置位于焊缝边界处的热机影响区。为研究异质FSW焊接薄板的疲劳裂纹扩展特性，设计出不同试样进行了疲劳裂纹扩展试验，并进行了裂纹扩展速率（FCGR）对比分析。分析了残余应力对焊接试样疲劳裂纹扩展速率的影响，并对疲劳断裂后的断口进行了SEM电镜观察分析，总结异质搅拌摩擦焊接接头的断口特性。为两种航空铝合金的异质搅拌摩擦焊接结构的力学特性及疲劳性能评估奠定了基础。
关键词：搅拌摩擦焊，航空铝合金异质焊接，残余应力，应力应变曲线，疲劳裂纹扩展速率
Fatigue Property Of Dissimilar Fricition Stir Welded Aluminum Joint For Aircraft Structure1））
Ma YuE*,2)，Li Jiang*，Zhao Zhenqiang*
*( School of Aeronautics, Northwestern Polytechnical University，Xi’An 710072，China )
Abstract:Friction stir welding （FSW） technology can reduce weight,improve the comprehensive performance and save cost,particularly it can weld 2xxx and 7xxx aluminum alloys that can't welded by the tradition welding way, so FSWed integral structure is considered to be one of aeronautical structure in the future. The distribution of residual stress, mechanical properties and fatigue crack growth properties of dissimilar 2024-T3 and 7075-T6 thin friction stir welded plates have been studied in this paper. According to present research results in China and abroad, dissimilar 2024-T3 and 7075-T6 thin plates were welded by proper friction stir welding parameters. And then X-ray diffraction method was used to measure residual stress profiles in welded plates. For dissimilar welded plate, the residual stress doesn't present the 'double peak', and the residual stress in both sides of weld joint is asymmetric. And residual stress in 2024 side has a large fluctuation, while in 7075 side it keeps mainly tensile and has a smaller fluctuation. According to related standards, two different samples were designed. Then mechanical tests of dissimilar welded joints were performed to get the stress-strain curves along and perpendicular to the direction of the weld. Fracture surfaces were studied and compared. For the dissimilar welded samples, the stress-strain curve is between curves of monolithic welded joints, and fracture surface is zigzag. Fracture points of the sample with perpendicular weld are located in the heat affected zone near the border of the weld line. In order to study fatigue crack growth of dissimilar thin welded plates, seven kinds of samples were designed to perform the fatigue crack propagation tests. Fatigue crack growth rates （FCGR） were compared with each other and parent material to analyze the influence of residual stress on fatigue crack growth rate. And SEM was used to analyze the fatigue fracture surfaces. The feature of fracture surfaces was summarized. All results provide useful information for fatigue analysis of FSWed aircraft structure.
Key words:Friction stir welding,dissimilar joint of aluminum alloy for aircraft application, residual stress, stress-strain curve, fatigue crack growth rate
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