Microstructure and mechanical properties of alumina-6061 aluminum alloy joined by friction welding

The study of the interface of ceramic/metal alloy friction welded components is essential for understanding of the quality of bonding between two dissimilar materials. In the present study, optical and electron microscopy as well as four-point bending strength and microhardness measurements were used to evaluate the quality of bonding of alumina and 6061 aluminum alloy joints produced by friction welding. The joints were also examined with EDX (energy dispersive X-ray) in order to determine the phases formed during welding. The bonded alumina-6061 aluminum samples were produced by varying the rotational speed but keeping constant the friction pressure and friction time. The experimental results showed that the effect of rotation speed and degree of deformation appears to be high on the 6061 Al alloy than on the alumina part. It is discovered that the weld interface formed included three different regions: unaffected zone (UZ), deformed zone (DZ), as well as transformed and recrystallized fully deformed zone (FPDZ). Therefore, when rotational speed increases, the thickness of full plastic deformed zone (FPDZ) at the interface increases as a result of more mass discarded from the welding interface. It was also observed that rotational speed of 2500 rpm can produce a very good joint and microhardness with good microstructure as compared to the other experimental rotational speeds.     

Fabrication of large-bulk ultrafine grained 6061 aluminum alloy by rolling and low-heat-input friction stir welding

In this study, the ultrafine grained (UFG) 6061 Al alloys fabricated by cold rolling were friction stir welded (FSW) with different rotation rates under both air cooling and rapid cooling in water. Low-heat-input parameters of 400 rpm rotation rate in water (400-Water) could effectively inhibit the coarsening of recrystallized grains, reduce the precipitation rate, and retain more dislocations of the UFG 6061 Al parent metal. 400-Water joint showed high lowest-hardness value, narrow low-hardness zone, and high tensile strength, attributing to the effect of dislocation, grain boundary, solid-solution, and precipitation hardening. This work provides an effective strategy to fabricate large-sized bulk UFG Al alloy by cold rolling with large deformation and low-heat-input FSW.     

Numerical simulation and experimental investigation on friction stir welding of 6061-T6 aluminum alloy

A modified three-dimensional model was established to simulate the friction stir welding of the 6061-T6 aluminum alloy. A detailed calculating method of the heat generation was proposed by taking account of the contact conditions between the tool and the work-piece. The results show that the heat mainly generated within the region close to the shoulder, the high temperature exists within the upper portion of the weld and decreases along the thickness direction. The strong material flow mainly occurs within the region around the tool and the material ahead of the tool sweeps toward the RS and finally deposits behind the tool. During this procedure the material is extruded to experience different shear orientations, and a defect-prone region exists in the region where material flow is weak. The temperature field and material flow behaviors predicted by the simulation method are in good agreement with the results obtained by the experiments.     

Tensile behavior of friction stir welded AA 6061-T4 aluminum alloy joints

In this investigation response surface methodology based on a central composite rotatable design with three parameters, five levels and 20 runs, was used to develop a mathematical model predicting the tensile properties of friction stir welded AA 6061-T4 aluminum alloy joints at 95% confidence level. The three welding parameters considered were tool rotational speed, welding speed and axial force. Analysis of variance was applied to validate the predicted model. Microstructural characterization and fractography of joints were examined using optical and scanning electron microscopes. Also, the effects of the welding parameters on tensile properties of friction stir welded joints were analyzed in detail. The results showed that the optimum parameters to get a maximum of tensile strength were 920 rev/min, 78 mm/min and 7.2 kN, where the maximum of tensile elongation was obtained at 1300 rev/min, 60 mm/min and 8 kN.     

Investigation on dissimilar underwater friction stir lap welding of 6061-T6 aluminum alloy to pure copper

Friction stir welding (classical FSW) is considered to offer advantages over the traditional fusion welding techniques in terms of dissimilar welding. However, some challenges still exist in the dissimilar friction stir lap welding of the aluminum/copper (Al/Cu) metallic couple, among which the formation of the Al–Cu intermetallic compounds is the major problem. In the present research, due to the fact that the formation and growth of the intermetallic are significantly controlled by the thermal history, the underwater friction stir welding (underwater FSW) was employed for fabricating the weld, and the weld obtained by underwater FSW (underwater weld) was analyzed via comparing with the weld obtained under same parameters by classical FSW (classical weld). In order to investigate the effect of the external water on the thermal history, the K-type thermocouple was utilized to measure the weld temperature, and it is found that the water could decrease the peak temperature and shorten the thermal cycle time. The XRD results illustrate that the interface of the welds mainly consist of the Al–Cu intermetallic compounds such as CuAl₂ and Cu₉Al₄ together with some amounts of Al and Cu, and it is also found that the amount of the intermetallic in the underwater weld is obvious less than in the classical weld. The SEM images and the EDS line scan results also illustrate that the Al–Cu diffusion interlayer at the Al–Cu interface of the underwater weld was obviously thinner than that of the classical weld.     

Refill friction stir spot welding of 5083-O aluminum alloy

In this work,refill friction stir spot welding(RFSSW) was used to weld 2 mm-thick 5083-O alloy.The Box–Behnken experimental design was used to investigate the effect of welding parameters on the joint lap shear property.Results showed that a surface indentation of 0.3 mm effectively eliminated the welding defects.Microhardness of the stir zone(SZ) was higher than that of the base material(BM) and the hardness decreased with increasing the heat input during welding.The optimum failure load of 7.72 k N was obtained when using rotating speed of 2300 rpm,plunge depth of 2.4 mm and refilling time of 3.5 s.Three fracture modes were obtained during the lap shear test and all were affected by the hook defect.     

Defects and tensile properties of 6013 aluminum alloy T-joints by friction stir welding

In this paper, 6013-T4 T-joints were successfully fabricated with different welding parameters by friction stir welding in two different combination modes of skins and stringers. The distribution features and formation mechanisms of defects in T-joints were observed and analyzed. The effect of defects and welding parameters on tensile properties of T-joints was investigated. The result shows that the T-joint without tunnel defect only can be obtained with the traverse speed of 100 mm/min in this experiment, and the welding parameters influence the features and sizes of kissing bond defects. The fracture of T-joints along the shin is attributed to the kissing bond defect and the tunnel defect is the main factor affecting the tensile properties along the stringer.     

Process optimization in the self-reacting friction stir welding of aluminum 6061-T6

Self-reacting friction stir welding (SR-FSW), also called bobbin-tool friction stir welding (BT-FSW), is a solid state welding process similar to friction stir welding (FSW) except that the tool has two opposing shoulders instead of the shoulder and a backing plate found in FSW. The tool configuration results in greater heat input and a symmetrical weld macrostructure. A significant amount of information has been published in the literature concerning traditional FSW while little has been published about SR-FSW. An optimization experiment was performed using a factorial design to evaluate the effect of process parameters on the weld temperature, surface and internal quality, and mechanical properties of self-reacting friction stir welded aluminum alloy 6061-T6 butt joints. The parameters evaluated were tool rotational speed, traverse speed, and tool plunge force. A correlation between weld temperature, defect formation (specifically galling and void formation), and mechanical properties was found. Optimum parameters were determined for the welding of 8-mm-thick 6061-T6 plate.     

Characterization of friction stir welded boron carbide particulate reinforced AA6061 aluminum alloy stir cast composite

Development of welding procedures to join aluminum matrix composite (AMCs) holds the key to replace conventional aluminum alloys in many applications. In this research work, AA6061/B₄C AMC was produced using stir casting route with the aid of K₂TiF₆ flux. Plates of 6 mm thickness were prepared from the castings and successfully butt joined using friction stir welding (FSW). The FSW was carried out using a tool rotational speed of 1000 rpm, welding speed of 80 mm/min and axial force of 10 kN. A tool made of high carbon high chromium steel with square pin profile was used. The microstructure of the welded joint was characterized using optical and scanning electron microscopy. The welded joint showed the presence of four zones typically observed in FSW of aluminum alloys. The weld zone showed fine grains and homogeneous distribution of B₄C particles. A joint efficiency of 93.4% was realized under the experimental conditions. But, FSW reduced the ductility of the composite.     

Microstructure and mechanical properties of dissimilar friction stir welding of 6061-to-7050 aluminum alloys

In this work, the microstructure and mechanical properties of friction stir welded dissimilar butt joints of 6061-to-7050 aluminum alloys were evaluated. Microstructure analysis of the cross-section of the joints revealed distinct lamellar bands and various degrees of intermixing that were correlated with tool rotational speed. Due to the distinct mechanical properties of the two alloys, microhardness measurements showed a consistent asymmetric hardness distribution profile across the weld nugget, regardless of tool rotational speed. Under monotonic tensile loading, an increase in the joint strength was observed with the increase in the tool rotational speed. Regarding fracture, the joints consistently failed on the 6061 aluminum alloy side. Furthermore, two modes of failure were observed, one through the stir zone and the other through the heat-affected zone. Inspection of the fracture surfaces suggested that inadequate material intermixing produced at low tool rotational speeds was the cause for the low mechanical strength and failure through the stir zone. On the other hand, the failure observed through the heat-affected zone at high rotational speeds was produced due to the material softening as confirmed by the microhardness measurements.     

Study of friction stir welding of aluminum

A half-cold hardening aluminum plate were friction-stir welded at various rotation speeds (850–1860 rpm) and travel rates of 30 to 160 mm/min with welding forces ranging between 2.5 and 10 MPa using different dimension welding heads. Experimental results show that the dimensions of the welding head are critical to produce sound welds. The microstructure of the weld is characterized by its much finer and equiaxed grains as contrasted with the coarse and band-like structure of the parent aluminum plate. Tensile strength of the welds is about 20% lower than that of the hardening aluminum plate, but about 10% higher microhardness is demonstrated by the welds in comparison with that of the aluminum plate in annealing condition. Moreover, travel rate of the welding head pin has a strong effect on microhardness and tensile strength of the FSW welds, and the ratio of rotation speed and travel rate of the head should be in a reasonable range to obtain high performance welds. The variables of the welding process are also discussed in terms of heat balance and energy input of the welds.     

铝合金搅拌摩擦焊超声检测研究进展EI北大核心CSCD

铝合金搅拌摩擦焊(friction stir welding, FSW)焊接参数选择不当将会产生隧道孔、未焊透(lack of penetration, LOP)和吻接等取向复杂、细微紧贴的缺陷。首先,本文简述了FSW焊缝与典型缺陷特征,总结了超声检测时面临纵向分辨力低、缺陷表征不完整、材料与缺陷声阻抗接近和灵敏度不足等难点。随后,从常规超声、超声衍射时差法(time-of-flight diffraction, TOFD)、相控阵超声检测技术和其他超声检测技术等方面综述了现有的铝合金FSW超声检测研究工作。最后,结合超声信号处理方法和机器学习方法对研究前景进行展望:可以通过分析和提取信号特征,进一步提升超声检测分辨力和信噪比,并实现取向复杂缺陷和细微紧贴缺陷的精准辨识与定量。     

Microstructure and mechanical properties of spray formed 7055 aluminum alloy by underwater friction stir welding

Ultra-high strength spray formed 7055 aluminum alloy in which Zn is supersaturated solid solution requires strict control of heat input in welding process. In this paper, underwater friction stir welding is carried out in order to reduce heat input comparing with traditional friction stir welding and further improve the joint performances by varying welding temperature history. Through comparing the thermal cycle curves and distribution of residual stress of the plate welded in different media, the reason why the joint welded underwater shows a better performance is figured out. The result shows that tensile strength, hardness and plasticity of underwater welded joint are better than that welded in air. The underwater joint has a fine grained microstructure without “S line” defect, a typically distinct boundary between the weld nugget zone and the thermal mechanically affected zone and a narrow heat affected zone. The main strengthening phase in underwater joint is MgZn₂ .     

2195铝锂合金搅拌摩擦焊接头盐雾腐蚀行为研究

本文研究了厚度为8 mm的2195铝锂合金母材及搅拌摩擦焊接头在3.5wt.％NaCl介质中的盐雾腐蚀行为,计算了不同腐蚀周期下的腐蚀速率,并通过OM、SEM、TEM观察分析母材与焊核区的腐蚀微观形貌.结果 表明:2195铝锂合金母材及搅拌摩擦焊接头在3.5％ NaCl腐蚀介质中的主要腐蚀形式为点蚀,随时间的延长发展为...     

Predicting residual distortion of aluminum alloy stiffened sheet after friction stir welding by numerical simulation

Friction stir welding (FSW) has been widely applied in aluminum alloy manufacturing with its advantages of low residual stress and small deformation. But some FSW cases indicated that the residual distortion was still significant if a large size sheet be welded. In order to reduce the residual distortion of large aluminum alloy sheet after FSW, a general method adopted in this paper was that some stiffeners were designed on the sheet before it be welded. The process of FS-welded structure (sheet with stiffeners) was numerically simulated by finite element analysis (FEA) method. Based on the numerical simulation, the residual distortion of the structure was predicted and the effect of stiffeners was investigated. First, a three-dimensional FEA model was developed to analyze the welding process on a sheet, and the simulation results were verified by FSW experiments. Then, the verified model was applied on structure to compute residual distortion. The prediction displayed that the distortion pattern of structure was convex in longitudinal direction and concave in transversal direction after FSW. In simulation results, the distortion shape of structure was similar to that of sheet, but the distortion value of structure was much smaller. The comparison of simulation results showed that the residual plastic strain generated by FSW on the sheet and the structure was nearly the same, so the part of distortion which was reduced by stiffeners was the distortion induced by buckling.     

Microstructural and mechanical analysis of 6063-T6 aluminum alloy joints bonded by friction stir welding

Journal of Materials Science - For improving the comprehensive mechanical properties of aluminum alloys (AAs) joint, the 6063-T6 AAs with thickness of 10 mm were bonded via the...     

Gradient micro-structured surface layer on aluminum alloy fabricated by in situ rolling friction stir welding

A gradient micro-structure was formed in the surface layer of 2219 aluminum alloy joint by means of in situ rolling friction stir welding (IRFSW). The micro-structured surface layer is about 200 μm deep, corresponding to a gradient change in microhardness from 86.8 to 59.4 HV in the coarse-grained weld nugget zone (WNZ). Compared with those of the base material, the friction coefficient values are evidently decreased and the wear resistance is obviously enhanced on the surface layer. The corrosion current was relatively low and corrosion potential value was positive with respect to that of the base material. The second-phase particles in the upper surface layer were much more and smaller than those of the base material.     

Mathematical model and optimization for underwater friction stir welding of a heat-treatable aluminum alloy

During the friction stir welding (FSW) of heat-treatable aluminum alloys, the welding thermal cycles tend to cause a local softening in the joints and thus lead to a degradation in joint properties. Underwater FSW has been demonstrated to be available for the strength improvement of normal joints. In order to obtain the optimum welding condition for underwater FSW, a 2219-T6 aluminum alloy was underwater friction stir welded and a mathematical model was developed to optimize the welding parameters for maximum tensile strength in the present study. The results indicate that a maximum tensile strength of 360 MPa can be achieved through underwater FSW, higher than the maximum tensile strength obtained in normal condition.     

Corrosion fatigue behaviour of aluminium alloy 6061-T651 welded using fully automatic gas metal arc welding and ER5183 filler alloy

The fatigue life of aluminium 6061-T651 at various applied stress amplitudes in the unwelded and welded condition was found to be significantly reduced on immersion in a 3.5% NaCl simulated sea water solution, compared to that measured in ambient air. The ratio of fatigue life in NaCl test solution to that in air increased as the stress amplitude decreased. The observed reduction in the fatigue life in the NaCl test solution was most likely due to the presence of pits which nucleated on second phase particles or precipitates. Welded joints performed using pulsed gas metal arc welding and ER5183 filler wire failed at the interface between the weld metal and the heat-affected zone as a result of a high pitting rate in this region.