铝合金搅拌摩擦点焊接头动态力学性能研究
发布时间：2018-11-07 18:04
【摘要】：6082-T6铝合金具有较高的比强度、优异的耐腐蚀性和良好的焊接性能,被广泛应用于高速轨道列车和航空航天生产领域。搅拌摩擦点焊是一种新型的搭接式固相连接方法。目前,关于6082-T6铝合金FSSW接头动态力学性能的研究相对较少。因此,本文主要针对2.5mm厚的6082-T6铝合金板材进行了FSSW实验,系统地研究了不同焊接工艺下FSSW接头的准静态力学性能、高周疲劳性能、高速冲击性能。FSSW接头动态力学性能的研究对FSSW接头在服役条件下预防失效具有重要的指导意义。准静态力学性能试验结果表明:无匙孔FSSW的最大拉剪强度可达8.05KN,而FSSW和搅拌摩擦胶点焊接头分别为4.75KN和6.0KN,它们的接头强度明显低于无匙孔FSSW接头,这是由于无匙孔FSSW接头所形成的有效焊合面积较另外两种焊接接头而言较大,且抗变形能力强。并且在加载的过程中,三种搅拌摩擦点焊接头所表现出的断裂方式也不同,其中,搅拌摩擦胶点焊接头的断裂方式为胶层断裂和焊点断裂的机械混合,这是由于搅拌摩擦胶点焊接头是胶接与搅拌摩擦点焊两种连接方式的复合连接。高周疲劳性能试验结果表明:在同一加载载荷水平下,无匙孔FSSW接头的疲劳性能最好,有匙孔搅拌摩擦胶点焊接头的疲劳性能次之,有匙孔FSSW接头的疲劳性能最差;不同FSSW接头的疲劳试验数据具有很好的规律性,且加载载荷与疲劳寿命呈指数型函数关系;循环加载达到稳定阶段后,无匙孔FSSW接头、FSSW接头和搅拌摩擦胶点焊接头在单个循环周期内的循环滞回能分别达到0.72MJ/m3、0.35 MJ/m3和0.36 MJ/m3;从疲劳宏观断裂方式可观察到疲劳裂纹沿着界面间隙向板厚方向扩展,且无匙孔FSSW接头的宏观断口中均存在二次裂纹;依据FSSW接头内存在的缺陷和疲劳宏观断裂方式,初步建立了一种简单的疲劳裂纹扩展模型,用于评定疲劳裂纹的扩展及疲劳寿命。对无匙孔FSSW接头的四个区域分别进行分离式霍普金森压杆试验,试验结果表明:母材区、焊核区和热机影响区在动态加载过程中的变形协调能力很好,抗动态冲击能力较强,而热影响区的抗动态冲击能力较差。母材区的材料的冲击吸收功为9.068MJ·m-3,焊核区材料的冲击吸收功为9.85MJ·m-3,热机影响区材料的冲击吸收功为8.36MJ·m-3,热影响区材料的冲击吸收功为1.34MJ·m-3;四个区域的绝热剪切敏感性都较小。为了分析准静态拉伸剪切断裂和高周疲劳断裂的机制,对拉剪断口和疲劳断口进行了SEM观察发现:无匙孔FSSW接头和搅拌摩擦胶点焊接头的拉剪断口中裂纹扩展区存在准解理面,而FSSW接头的拉剪断口中扩展区存在“舌片状花样”,在瞬断区均存在着韧窝,所以拉伸剪切断裂均是准解理断裂和韧性断裂的混合断裂,无匙孔FSSW接头拉伸剪切断口瞬断区存在大量的等轴韧窝,说明其接头的塑性较好;三种FSSW接头的疲劳断裂方式也是准解理断裂和韧性断裂的混合断裂。
[Abstract]:6082-T6 aluminum alloy has high specific strength, excellent corrosion resistance and good welding performance, so it is widely used in high-speed rail train and aerospace production field. Friction stir spot welding (FSW) is a new type of lap-type solid-phase bonding method. At present, there are few studies on the dynamic mechanical properties of 6082-T6 aluminum alloy FSSW joints. Therefore, in this paper, the quasi-static mechanical properties and high cycle fatigue properties of FSSW joints under different welding processes are systematically studied by means of FSSW experiments on 6082-T6 aluminum alloy plates with 2.5mm thickness. The study of dynamic mechanical properties of FSSW joints is of great significance to prevent the failure of FSSW joints under the condition of service. The results of quasi-static mechanical properties test show that the maximum tensile shear strength of keyhole free FSSW is 8.05 KN, while that of FSSW and friction stir joint is 4.75KN and 6.0 KN, respectively, and their joint strength is obviously lower than that of FSSW joint without keyhole. This is because the effective soldering area of the keyhole free FSSW joint is larger than that of the other two welded joints, and the deformation resistance is strong. In the process of loading, the fracture modes of the three friction stir spot welding joints are different, among them, the fracture mode of friction stir glue spot welding joint is the mechanical mixing of rubber layer fracture and solder joint fracture. This is because the friction stir spot welding joint is a compound connection of glue and friction stir spot welding. The results of high cycle fatigue test show that under the same loading load, the fatigue performance of FSSW joints with keyhole is the best, the fatigue performance of FSW joints with keyhole is the second, and the fatigue performance of FSSW joints with keyhole is the worst. The fatigue test data of different FSSW joints have good regularity, and the relationship between loading load and fatigue life is exponential. After cyclic loading reached the stable stage, the cyclic hysteresis energies of keyhole free FSSW joints, FSSW joints and friction stir spot welding joints reached 0.72 MJ / m3 0.35 MJ/m3 and 0.36 MJ/m3; respectively in a single cycle. From the fatigue macroscopic fracture mode, it can be seen that the fatigue crack propagates along the interface gap to the thickness direction of the plate, and there are secondary cracks in the macroscopic fracture of the FSSW joint without keyhole. According to the defects in FSSW joints and the fatigue macroscopic fracture mode, a simple fatigue crack propagation model is established to evaluate the fatigue crack propagation and fatigue life. The split Hopkinson compression bar tests were carried out on the four regions of the keyhole free FSSW joint. The results show that the deformation coordination ability of the base metal zone, the nuke zone and the affected zone of the heat engine is good during the dynamic loading process, and the resistance to dynamic impact is relatively strong. However, the heat affected zone has poor dynamic impact resistance. The impact absorption energy of the base material is 9.068MJ m-3, the impact absorption energy of the material in the nuke zone is 9.85MJ m-3, and the impact absorption energy of the material in the heat machine-affected zone is 8.36MJ m-3. The impact absorption energy of the heat-affected zone materials is 1.34MJ m-3; The adiabatic shear sensitivity of the four regions is small. In order to analyze the mechanism of quasi static tensile shear fracture and high cycle fatigue fracture, the SEM observation of tensile shear fracture and fatigue fracture surface shows that there is a quasi cleavage surface in the crack growth zone of the tensile shear mouth of the FSSW joint without keyhole and friction stir glue spot welding joint. However, there are "tongue flake patterns" in the extension region of the tensile shear mouth of FSSW joint and dimples in the transient fracture zone, so the tensile shear fracture is a mixed fracture of quasi-cleavage and ductile fracture. There are a large number of equiaxed dimples in the tensile shear fracture zone of FSSW joints without keyhole, which indicates that the joints have good plasticity. The fatigue fracture modes of three kinds of FSSW joints are also quasi-cleavage fracture and ductile fracture mixed fracture.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.14
本文编号：2317149
[Abstract]:6082-T6 aluminum alloy has high specific strength, excellent corrosion resistance and good welding performance, so it is widely used in high-speed rail train and aerospace production field. Friction stir spot welding (FSW) is a new type of lap-type solid-phase bonding method. At present, there are few studies on the dynamic mechanical properties of 6082-T6 aluminum alloy FSSW joints. Therefore, in this paper, the quasi-static mechanical properties and high cycle fatigue properties of FSSW joints under different welding processes are systematically studied by means of FSSW experiments on 6082-T6 aluminum alloy plates with 2.5mm thickness. The study of dynamic mechanical properties of FSSW joints is of great significance to prevent the failure of FSSW joints under the condition of service. The results of quasi-static mechanical properties test show that the maximum tensile shear strength of keyhole free FSSW is 8.05 KN, while that of FSSW and friction stir joint is 4.75KN and 6.0 KN, respectively, and their joint strength is obviously lower than that of FSSW joint without keyhole. This is because the effective soldering area of the keyhole free FSSW joint is larger than that of the other two welded joints, and the deformation resistance is strong. In the process of loading, the fracture modes of the three friction stir spot welding joints are different, among them, the fracture mode of friction stir glue spot welding joint is the mechanical mixing of rubber layer fracture and solder joint fracture. This is because the friction stir spot welding joint is a compound connection of glue and friction stir spot welding. The results of high cycle fatigue test show that under the same loading load, the fatigue performance of FSSW joints with keyhole is the best, the fatigue performance of FSW joints with keyhole is the second, and the fatigue performance of FSSW joints with keyhole is the worst. The fatigue test data of different FSSW joints have good regularity, and the relationship between loading load and fatigue life is exponential. After cyclic loading reached the stable stage, the cyclic hysteresis energies of keyhole free FSSW joints, FSSW joints and friction stir spot welding joints reached 0.72 MJ / m3 0.35 MJ/m3 and 0.36 MJ/m3; respectively in a single cycle. From the fatigue macroscopic fracture mode, it can be seen that the fatigue crack propagates along the interface gap to the thickness direction of the plate, and there are secondary cracks in the macroscopic fracture of the FSSW joint without keyhole. According to the defects in FSSW joints and the fatigue macroscopic fracture mode, a simple fatigue crack propagation model is established to evaluate the fatigue crack propagation and fatigue life. The split Hopkinson compression bar tests were carried out on the four regions of the keyhole free FSSW joint. The results show that the deformation coordination ability of the base metal zone, the nuke zone and the affected zone of the heat engine is good during the dynamic loading process, and the resistance to dynamic impact is relatively strong. However, the heat affected zone has poor dynamic impact resistance. The impact absorption energy of the base material is 9.068MJ m-3, the impact absorption energy of the material in the nuke zone is 9.85MJ m-3, and the impact absorption energy of the material in the heat machine-affected zone is 8.36MJ m-3. The impact absorption energy of the heat-affected zone materials is 1.34MJ m-3; The adiabatic shear sensitivity of the four regions is small. In order to analyze the mechanism of quasi static tensile shear fracture and high cycle fatigue fracture, the SEM observation of tensile shear fracture and fatigue fracture surface shows that there is a quasi cleavage surface in the crack growth zone of the tensile shear mouth of the FSSW joint without keyhole and friction stir glue spot welding joint. However, there are "tongue flake patterns" in the extension region of the tensile shear mouth of FSSW joint and dimples in the transient fracture zone, so the tensile shear fracture is a mixed fracture of quasi-cleavage and ductile fracture. There are a large number of equiaxed dimples in the tensile shear fracture zone of FSSW joints without keyhole, which indicates that the joints have good plasticity. The fatigue fracture modes of three kinds of FSSW joints are also quasi-cleavage fracture and ductile fracture mixed fracture.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.14
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