Analysis of process parameters effects on friction stir welding of dissimilar aluminum alloy to advanced high strength steel

Thin sheets of aluminum alloy 6061-T6 and one type of Advanced high strength steel, transformation induced plasticity (TRIP) steel have been successfully butt joined using friction stir welding (FSW) technique. The maximum ultimate tensile strength can reach 85% of the base aluminum alloy. Intermetallic compound (IMC) layer of FeAl or Fe₃Al with thickness of less than 1 μm was formed at the Al–Fe interface in the advancing side, which can actually contribute to the joint strength. Tensile tests and scanning electron microscopy (SEM) results indicate that the weld nugget can be considered as aluminum matrix composite, which is enhanced by dispersed sheared-off steel fragments encompassed by a thin intermetallic layer or simply intermetallic particles. Effects of process parameters on the joint microstructure evolution were analyzed based on mechanical welding force and temperature that have been measured during the welding process.     

镁合金搅拌摩擦焊接工艺参数优化

为了优化镁合金搅拌摩擦焊接工艺参数,对5 mm厚镁合金AZ31B板材的搅拌摩擦焊接技术进行了试验研究,利用SN比实验设计,对镁合金AZ31B搅拌摩擦焊接工艺参数进行了方差分析,优化了搅拌头的材料、结构,最终确定搅拌头的材料为W6Mo5Cr4V2,结构为凹面圆台形.轴肩尺寸为12 mm.探针的根部直径为5.5 mm,端部直径为2.5 mm,长度为4.7 mm.获得镁合金AZ31B搅拌摩擦焊的工艺参数显著性顺序为旋转速度、横向速度和压力;确定了镁合金AZ31B搅拌摩擦焊的最优工艺参数为1500 r/min、47.5 mm/min、3kN.     

Dissimilar lap joining of 304 stainless steel to CP-Ti employing friction stir welding

A 304 stainless steel plate was lap joined to a CP-Ti one by friction stir welding technique. Stainless steel was selected as the top member. Sound dissimilar joints were achieved using an advancing speed of 50 mm/min and rotation speeds in the range of 700–1100 rpm. A region of vortices of bimetallic weld of 304 stainless steel and CP-Ti was formed in the lap joint fabricated using the highest applied tool rotation speed; this was associated with plasticizing of both members with the aid of a double-shoulder tool. In addition, due to complex material flow, mechanical interlock features were shaped that consists of extruded stainless steel into the plasticized titanium region. A maximum shear strength value of ∼119 MPa was achieved; this was found to be close to that of CP-Ti. The lap joint was strengthened by the formation of vortices of bimetallic weld of 304 stainless steel and CP-Ti and mechanical interlock features at joint interface due to complex materials flow.     

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.     

Optimization of friction stir welding parameters for dissimilar aluminum alloys

Assembly consisting of cast and wrought aluminum alloys has wide spread application in defense and aero space industries. For the efficacious use of the transition joints, the weld should have adequate strength and formability. In the present investigation, A356 and 6061 aluminum alloys were friction stir welded under tool rotational speed of 1000–1400 rpm and traversing speed of 80–240 mm/min, keeping other parameters same. The variable process window is responsible for the change in total heat input and cooling rate during welding. Structural characterization of the bonded assemblies exhibits recovery-recrystallization in the stirring zone and breaking of coarse eutectic network of Al–Si. Dispersion of fine Si rich particles, refinement of 6061 grain size, low residual stress level and high defect density within weld nugget contribute towards the improvement in bond strength. Lower will be the tool rotational and traversing speed, more dominant will be the above phenomena. Therefore, the joint fabricated using lowest tool traversing and rotational speed, exhibits substantial improvement in bond strength (∼98% of that of 6061 alloy), which is also maximum with respect to others.     

Effect of welding parameters on the strain rate and microstructure of friction stir spot welded 2024 aluminum alloy

The stir zone microstructure, crystallographic texture, temperature and strain rate in the stir zones produced during Al 2024 spot welding using different tool rotational speed settings are investigated. The calculated strain rate during spot welding decreases from 1600 to 0.6 s⁻¹ when the tool rotational speed increases from 750 to 3000 rpm. The low strain rate values are associated with tool slippage resulting from spontaneous melting of S phase particles at temperatures ≥490 °C. However, the calculated strain rate is 1600 s⁻¹ in Al 2024 spot welds made using tool rotational speed of 750 rpm since the temperature never reaches 490 °C. Material transfers downwards via that pin thread during the dwell period in Al 2024 spot welding. It is proposed that this downward transfer of material provides a continuous supply of undissolved S phase particles, which melt spontaneously when the welding parameter settings produce stir zone temperatures ≥490 °C. A weak crystallographic texture where the {100} planes are oriented at about 45° to the θ-direction exists in the stir zones of spot welds made using different tool rotational speeds (from 750 to 3000 rpm). Another crystallographic texture where the {100} planes are parallel to the Z-direction (to the tool axis) is stronger in spot welds made using higher tool rotational speed settings. Also, material located at the root of the pin thread has a quite different crystallographic texture from that in the bulk of the stir zone.     

Effect of welding parameters on microstructure and mechanical properties of friction stir spot welded 5052 aluminum alloy

Friction stir spot welding (FSSW) is a newly-developed solid state joining technology. In this study, two types of FSSW, normal FSSW and walking FSSW, are applied to join the 5052-H112 aluminum alloy sheets with 1 mm thickness and then the effect of the rotational speed and dwell time on microstructure and mechanical properties is discussed. The lower sheet material underneath the hook didn’t flow into the upper sheet due to the concave surface in the shoulder and groove in the anvil. The hardness profile of the welds exhibited a W-shaped appearance and the minimum hardness was measured in the HAZ. The results of tensile/shear tests and cross-tension tests indicate that the joint strength decreases with increasing rotational speed, while it’s not affected significantly by dwell time. At the rotational speed of 1541 rpm, the tensile/shear strength and cross-tension strength reached the maximum of 2847.7 N and 902.1 N corresponding to the dwell time of 5 s and 15 s. Two different fracture modes were observed under both tensile/shear and cross-tension loadings: shear fracture and tensile/shear mixed fracture under tensile/shear loadings, and nugget debonding and pull-out under cross-tension loadings. The performance of the welds plays a predominant role in determining the type of fracture modes. In addition, the adoption of walking FSSW brings unremarkable improvements in weld strength.     

Dissimilar metal joining of ZK60 magnesium alloy and titanium by friction stir welding

Friction stir welding (FSW) is a solid-state joining process, and the joining temperature is lower than that in the fusion welding process. The effect of alloying elements on the microstructure of dissimilar joints of a Mg–Zn–Zr alloy (ZK60) and titanium by using FSW, was examined. A commercial ZK60 and a titanium plates with 2 mm in thickness was butt-joined by inserting the probe into the ZK60 plate, and slightly offset into the titanium plate side to ensure the direct contact between them. The average tensile strength of the joint was 237 MPa, which was about 69% of that of ZK60 and a fracture occurred mainly in the stir zone of ZK60 and partly at the joint interface. A thin Zn and Zr-rich layer with about 1 m in thickness was formed at the joint interface, which affected the tensile strength of the dissimilar joint of ZK60 and titanium.     

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。     

Effect of welding parameters on microstructure and mechanical properties of friction stir welded joints of AA7039 aluminum alloy

A high strength Al–Zn–Mg alloy AA7039 was friction stir welded by varying welding and rotary speed of the tool in order to investigate the effect of varying welding parameters on microstructure and mechanical properties. The friction stir welding (FSW) process parameters have great influence on heat input per unit length of weld, hence on temperature profile which in turn governs the microstructure and mechanical properties of welded joints. There exits an optimum combination of welding and rotary speed to produce a sound and defect free joint with microstructure that yields maximum mechanical properties. The mechanical properties increase with decreasing welding speed/ increasing rotary speed i.e. with increasing heat input per unit length of welded joint. The high heat input joints fractured from heat affected zone (HAZ) adjacent to thermo-mechanically affected zone (TMAZ) on advancing side while low heat input joints fractured from weld nugget along zigzag line on advancing side.     

Effect of friction stir welding parameters on microstructural characteristics and mechanical properties of 2219-T6 aluminum alloy joints

A 2219-T6 aluminum alloy was friction stir welded in the present study. The results indicate that the recrystallized grains in the weld nugget zone (WNZ) of the joints exhibit the largest size in the middle part and the smallest size in the lower part. Furthermore, the void defect is formed in the joint when the rotation speed or welding speed is quite high. As the rotation speed or welding speed increases, the tensile strength of the joint firstly increases to a maximum value and then sharply decreases due to the occurrence of void defect. During tensile test, the defect-free joints welded at lower rotation speed are fractured in the WNZ, while those welded at relatively high rotation speed tend to be fractured in the heat affected zone (HAZ) adjacent to the thermal mechanically affected zone (TMAZ) on the retreating side.     

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.     

铝/钢搅拌摩擦焊对接焊缝组织及机理研究

为了提高Q235钢板和6082-T6铝合金对接的连接强度,采用搅拌摩擦焊进行对接焊接.研究了不同尺寸和形状的搅拌头、转速、焊接速度和偏移量等对铝钢对接焊缝组织的影响,进而优化了搅拌摩擦焊工艺.实验结果表明:不同形状的搅拌头影响接头"钉子"形状,接头的不同位置处由于受到不同热循环和搅拌导致晶粒尺寸不同,从而影响接头的力学性能.当搅拌针旋转速度260 r/min,焊接速度16 mm/min,针头偏向铝侧0.2 mm时,所得焊缝的拉伸强度为141.204 MPa,为最佳工艺参数.在此最优参数下获得过渡层的厚度约为8μm,界面的主要成分是Fe Al3.     

Characteristics of the reverse dual-rotation friction stir welding conducted on 2219-T6 aluminum alloy

Reverse dual-rotation friction stir welding (RDR-FSW) has great potential to obtain appropriate welding conditions through adjusting the independently rotating tool pin and surrounding shoulder. The welding torque exerted on the workpiece by the reversely rotating shoulder also cancels off a part of the welding torque exerted by the rotating tool pin, thus the clamping requirement for the workpiece is also reduced. In the present paper, a tool system for the RDR-FSW was designed and successfully applied to weld high strength aluminum alloy 2219-T6, and then microstructures and mechanical properties of the optimized joint were investigated to demonstrate the RDR-FSW characteristics. The weld nugget zone was characterized by the homogeneity of refined grain structures, but there was a three-phase confluction on the advancing side formed by different grain structures from three different zones. The tensile strength of the optimized joint was 328 MPa (73.7% of the base material), showing an obvious improvement when compared with the optimized joint welded by the FSW without the reversely rotating assisted shoulder. The tensile fracture occurred in the ductile fracture mode and the fracture path propagated in the weakest region where the Vickers hardness is the minimum.     

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.     

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.     

Effects of welding speed on the microstructure and hardness in friction stir welding joints of 6005A-T6 aluminum alloy

The 6005A-T6 aluminum alloy was friction stir welded at different welding speeds. The peak temperature, microstructure and mechanical properties were examined for these joints. A special attention was devoted to the relationship between the precipitates evolution within different zones and the local hardness. In the nugget zone (NZ) experiencing the highest peak temperature, the β″ precipitates dissolved into α-Al matrix during welding, and the hardness of NZ depended on the level of natural aging (NA) at different welding speeds. The thermo-mechanically affected zone (TMAZ) is characterized by elongated grains with a high density of dislocations. The welding speed had not a significant effect on hardness in this zone. The heat-affected zone (HAZ) contains the transformation of β″–β′, the precipitation of Q′ and the coarsening of precipitates. The HAZ close to the joint center line exhibited the minimum hardness due to the coarsening of β′ and Q′ precipitates while the HAZ far from it having a high hardness level was mainly related to coherent β″ precipitates. The HAZ hardness and joint strength have an increased tendency with increasing the welding speed. It can be explained by increasing the density of Q′ or β″ precipitates.     

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.     

铝/钢异种金属的超声振动强化搅拌摩擦焊接工艺

采用新型超声振动强化搅拌摩擦焊接工艺实现了6061-T6铝合金以及QP980高强钢的搭接焊,对比分析了有无超声作用下,接头的宏观形貌、微观组织和拉伸剪切性能,同时研究了超声振动对焊接载荷的影响。结果表明:焊接前对母材施加超声振动,可以起到软化母材的作用,促进了材料的塑性流动,扩大了铝/钢界面区和焊核区,使更多的钢颗粒随搅拌针旋转进入铝合金侧,在界面区边缘形成钩状结构,进而提高了接头的失效载荷;超声改变了FSW接头断裂位置和断口形貌,提高了接头力学性能,在本实验工艺参数范围内,接头最大的平均失效载荷为4.99 kN;当焊接速度为90 mm/min,下压量为0.1 mm时,施加超声振动使接头的平均失效载荷提高了0.98 kN,拉剪性能提升28.24%;施加超声振动后轴向力F_z、搅拌头扭矩M_t和主轴输出功率分别下降2.46%,6.44%和4.59%。     

基于热力耦合模型铝合金搅拌摩擦焊接顺序优化仿真分析

基于所建立的搅拌摩擦焊接过程热输入模型和热力耦合有限元分析模型,对带圆孔铝合金板的搅拌摩擦焊接顺序进行了有限元研究,并得到了焊接过程中不同焊接方案下的温度、瞬态应力变化曲线以及焊后残余变形。通过综合比较可以看出,从两边向中间焊的方案2优于从中间向两边焊的方案1和从左向右的顺序焊接的方案3。此外,有限元模型求解结果和实验测量数据具有相当好的吻合。