Non-destructive inspection for weld joint of steel structure

Friction stir welding (FSW) succeeded in producing high quality dissimilar welds with AA5083 and A6N01 by evaluation of the microstructure and the root bend testing. A6N01 with a wide optimum range of welding condition should be placed on the retreating side to weld a sound joint between AA5083 and A6N01. The optimum welding condition of FSW for the dissimilar alloys between AA5083 and A6N01 was wider than that of AA5083. In the opposite orientation, A6N01 on the advancing side can hardly flow into AA5083 on the retreating side in front of the tool. As the pores on inappropriate welding conditions were observed, large pores on a lower tool rotation speed were different from small discontinuous pores on a higher tool rotation speed.     

Joint characteristics and dissimilar materials joining of pure-Al/5083 by friction stir welding

Friction stir welding (FSW)^1,2, developed in 1991 by The Welding Institute, UK is a joining process which overthrew welding concepts which existed at the time; its application has been progressed not only for soft alloys including aluminium, but also, in recent years, for steel.³ Sato and others carried out friction stir welding on 1080-O and 5083-O materials and investigated variations in the hardness.⁴ Ten years or so have passed since the development of friction stir welding, the process has been globally investigated and widely employed in various sectors such as vehicles, ships and the aerospace industry. Furthermore, investigations have also been carried out into the manufacture of dissimilar metal joints. For example, Enomoto studied 2024/AC4C cast alloy and reportedly obtained satisfactory joints.⁵ Li and others have investigated 2024/6061 and reported that both alloys are distributed at the weld zone in a stratified and complex manner.⁶     

轴肩尺寸对异种铝合金材料搅拌摩擦焊接头显微组织的影响规律

对5083铝/6082铝异种材料搅拌摩擦焊（friction stir welding,FSW）进行研究,重点分析轴肩直径对横截面形貌、显微组织与显微硬度的影响规律.结果表明,FSW接头焊核区由致密细小的等轴晶组成;增加轴肩直径可增加焊核区沿垂直焊缝方向的宽度以及增大焊核区、热影响区与热力影响区的晶粒尺寸.与后退侧的6082铝合金不同,前进侧5083铝合金的热力影响区发生了动态再结晶.显微硬度呈W形分布,最小值出现在热影响区.显微硬度的测试结果与焊核区的横截面形貌结果吻合.     

An apparatus for the determination of the shear and peel strengths in pad welds

Abstract

Friction stir welding (FSW)^1,2, developed in 1991 by The Welding Institute, UK is a joining process which overthrew welding concepts which existed at the time; its application has been progressed not only for soft alloys including aluminium, but also, in recent years, for steel.³ Sato and others carried out friction stir welding on 1080-O and 5083-O materials and investigated variations in the hardness.⁴ Ten years or so have passed since the development of friction stir welding, the process has been globally investigated and widely employed in various sectors such as vehicles, ships and the aerospace industry. Furthermore, investigations have also been carried out into the manufacture of dissimilar metal joints. For example, Enomoto studied 2024/AC4C cast alloy and reportedly obtained satisfactory joints.⁵ Li and others have investigated 2024/6061 and reported that both alloys are distributed at the weld zone in a stratified and complex manner.⁶     

Variations in stir zone and thermomechanically affected zone of dissimilar friction stir weld of AA5083 and AA6082 alloys

Variations in composition, microhardness (in the thermomechanically affected zone) and texture in the tool domain of the dissimilar friction stir weld of AA5083-O and AA6082-T6 alloys were investigated. The contents of the major alloying elements in the weld zones were determined using inductively coupled plasma?atomic emission spectroscopy. It was observed that a slight drop in the content of the alloying elements results from the friction stir welding process with the Mg content being the most affected amongst the major alloying elements in the two alloys. By relating the mass fractions of the major alloying elements in the parent metals of both alloys to those of the stir zone, the relative proportions of the two alloys in the stir zone were estimated with the results showing that at least 60% of the materials in the stir zone are from the retreating side of the weld. It was also revealed that the changes in the hardness profile in the thermomechanically affected zone of the retreating side are predominantly influenced by changes in grain size in that domain. Finally, the investigation further revealed that the texture component in the tool shoulder domain is different from the texture component in the tool pin domain.     

Effects of processing parameters on the friction stir spot joining of Al5083-O aluminum alloy to DP590 steel

Two dissimilar materials, aluminum alloy Al5083-O and advanced high strength steel DP590, were successfully joined by using friction stir spot joining (FSSJ). Satisfactory joint strengths were obtained at a rotational speed of 300 rpm and a plunge depth of 0.7 mm. Resulting joints were welded without a non-welded zone. This may be attributed to the enhanced smooth material flow owing to sufficient stirring effect and tool down force between the upper Al5083-O side and the lower DP590 side. The maximum tensile shear strength was 6.5 kN, which was higher than the joint strength required by the conventional method of resistance spot welding. The main fracture mode was plug fracture in the tensile shear test of joints. An intermetallic compound (IMC) layer with <6 μm thickness was formed at the joint interface, which meets the allowance value of <10 μm for the dissimilar material Al-Fe joints. Thus, the use of FSSJ to weld the dissimilar materials Al5083-O and DP590 resulted in mechanically and metallurgically sound joints.     

Base material location dependence of corrosion response in friction-stir-welded dissimilar 2024-to-5083 aluminum alloy joints

The effects of the base material (BM) location on the mechanical properties and the exfoliation corrosion performance of friction-stir-welded (FSWed) dissimilar 2024-to-5083 aluminum alloy joints were investigated. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), tensile tests and electrochemical experiments were conducted. The results revealed that the BM location had little effect on the tensile properties of the joints. The grain orientation spread (GOS) value of 2024 alloy side was lower than that of 5083 alloy side. Intergranular corrosion occurred mainly on the 2024 alloy side, while the grain interior of the 5083 alloy side was corroded due to the higher GOS value and dislocation density. The FSWed dissimilar joints with a superior exfoliation corrosion resistance could be achieved when the 5083 aluminum alloy with better corrosion performance was positioned on the retreating side.     

5052铝合金FSW接头组织和力学性能

采用搅拌摩擦焊焊接8 mm厚5052-O铝合金,并对焊接接头进行了显微组织观察和力学性能测试。结果表明:接头组织左右不对称,前进侧与母材分界线较明显,后退侧与母材分界线较模糊;焊接接头抗拉强度平均值为193.5 MPa,接头强度可达母材的99%,伸长率可达母材的84%;焊接接头正弯角和背弯角均可达到180°,弯曲性能良好;焊核区显微硬度约为72 HV,略高于母材,硬度最低点出现在前进侧熔合过渡区。     

基于CEL方法的Al/Mg搅拌摩擦焊温度场及材料混合流动研究

本文基于耦合欧拉-拉格朗日(CEL)方法建立5A06铝合金与AZ31B镁合金对接搅拌摩擦焊（FSW）的全热力耦合数值模型,并结合试验测试对Al/Mg异种金属FSW过程的温度场及材料混合流动特征进行研究。数值模拟所得特征点的温度循环曲线、焊缝表面形貌以及横截面上异种材料的混合分布状态均与试验结果吻合良好。在此基础上,采用质点追踪法对材料混合流动行为进行了深入分析。结果显示,高温区集中分布在轴肩下方区域,返回侧(Mg侧)温度较低温度梯度较大。焊缝区上表面材料熔合线偏向于前进侧(Al侧)。搅拌针附近材料流动剧烈,前进侧和返回侧的大部分材料都较均匀地沉积于搅拌针后方。前进侧与返回侧材料在水平和竖直方向上的交叉混合流动,最终形成了两种材料“咬合式”的界面特征。     

2219-T87铝合金搅拌摩擦焊接头组织与力学性能

采用搅拌摩擦焊方法对8mm厚2219-T87铝合金进行了焊接.对接头的宏观形貌、微观组织、显微硬度及断口形貌进行了分析.结果表明,焊核区为细小的等轴晶粒,晶粒尺寸远小于母材;热机影响区发生了弯曲变形;热影响区组织出现了明显粗化.前进边热机影响区和焊核区形成明显分界线,后退边相对模糊.搅拌摩擦焊对接头各区域沉淀相分布形态有重要影响.接头室温拉伸强度可以达到母材的70%以上.沿焊缝横截面的显微硬度的分布显示,硬度最低点位于后退侧热影响区区域,断裂位置位于后退侧热影响区处,接头的断裂形式为韧性断裂.     

2024/7075异种铝合金搅拌摩擦焊的晶体取向演化

使用光学显微镜、电子背散射衍射（EBSD）对比研究了2024/7075异种铝合金搅拌摩擦焊（FSW）接头及母材的组织特征、晶界特征和织构的演化.结果表明,后退侧热力影响区晶粒的小角度晶界含量较母材明显增大而前进侧热力影响区晶粒的小角度晶界含量与母材相比没有明显变化,焊核区发生了动态再结晶,大角度晶界含量明显增加.后退侧2024铝合金为弱取向组织,前进侧7075铝合金母材、热影响区以及热机影响区具有较强的S织构{123}<634>、黄铜织构{011}<211>和R织构{124}<211>,焊核区为等轴再结晶晶粒,没有明显的择优取向.     

Microstructure and Mechanical Properties of Low-Carbon Q235 Steel Welded Using Friction Stir Welding

This study focuses on the microstructure and mechanical properties of the joints of Q235 mild steel, which was formed by the friction stir welding (FSW). The results indicated that, after the FSW, the heat-affected zone (HAZ) of the retreating side (HAZ_RS) and the HAZ of the advancing side (HAZ_AS) recovered under the influence of the heating cycle. The transformation of the phases in the thermo-mechanically affected zone (TMAZ) of the retreating side (TMAZ_RS), the stir zone (SZ) and the TMAZ of the advancing side (TMAZ_AS) generated the pearlite and acicular ferrite. The continuous dynamic recrystallization occurred in all the three zones, whereas the grains were refined. The SZ mainly consisted of D₁, D₂ and F shear textures, while the TMAZ_AS was made up of only the F shear texture. The fine-grained structure, pearlite and the acicular ferrite improved the hardness and tensile strength of the joint. Its ultimate tensile strength was 479 MPa, which was 1.3% higher than that of the base metal. However, the uniform elongation was 16%, which showed a decrease of 33%. The fracture was a ductile fracture with the appearance of dimples. Besides, the joints of the FSW showed an excellent bending performance.     

Friction stir welding of dissimilar aluminium–magnesium joints: sheet mutual position effects

Abstract

Friction stir welding (FSW) is a solid state welding process used to weld difficult to be welded or unweldable materials as aluminium alloys. In the last years, other materials have been successfully tested as magnesium, titanium and nickel based alloys. Dissimilar joints can be obtained by FSW, but issues arise concerning the correct choice of the process parameters. In the paper, the results of an experimental and numerical campaign aimed to produce dissimilar AZ31-AA6016-T6 butt joints are presented. The effect of sheet mutual position and main process parameters was investigated. It was found that intermetallics are the main cause of the poor quality of the joints. Sound joints can be produced only if the magnesium alloy is in the advancing side.     

Electrochemical corrosion behaviour of stir zone of friction stir welded dissimilar joints of AA6061 aluminium–AZ31B magnesium alloys

Joining of dissimilar metals will offer many advantages in transportation sectors such as fuel consumption, weight reduction and emission reduction. However, joining of aluminium (Al) alloys with magnesium (Mg) alloys by fusion welding process is very complicated. Friction stir welding (FSW) is a feasible method to join these two dissimilar alloys. Mixing these two metals together in stir zone (SZ) leads to poor corrosion resistance. In this investigation, an attempt has been made to understand the corrosion resistance of SZ of FSWed dissimilar joints of AA6061 Al alloy and AZ31B Mg alloy. Potentiodynamic polarization test was conducted by varying chloride ion concentration, pH value of the NaCl solution and exposure time. The corroded surfaces were analyzed using optical microscopy, scanning electron microscopy and XRD techniques. Of these three factors investigated, exposure time is found to be the most significant factor to influence the corrosion behaviour of SZ of friction stir welded dissimilar joints of Al/Mg alloys.     

Fatigue Behavior of Dissimilar Al–Mg–Si/Al–Zn–Mg Aluminum Alloys Friction Stir Welding Joints

In this study, fatigue properties and fracture mechanism of dissimilar Al–Mg–Si/Al–Zn–Mg aluminum alloys friction stir welding(FSW) joints were investigated and the effect of the sheet configuration on the fatigue behavior of the FSW joints was also discussed. Results showed that the joints owned better fatigue properties when the Al–Zn–Mg aluminum alloy was placed at the advancing side(AS). At 10~7 cycles, the fatigue strengths of Al–Zn–Mg–AS and Al–Mg–Si–AS joints were, respectively, 105.6 and 90.1 MPa. All joints fractured at the heat-affected zone at the Al–Mg–Si alloy side. Transmission electron microscopy results showed that better fatigue property of the Al–Zn–Mg–AS joint was associated with the bridging effect of the bigger secondary phase particles.     

Pitting and stress corrosion cracking resistance of friction stir welded AA 5083

The corrosion behaviour of friction stir welded (FSW) joints of AA 5083 has been compared to that of MIG welded joints. Pitting and stress corrosion cracking (SCC) resistance in 3.5% NaCl + 0.3 g/l H₂O₂ and in EXCO (4 M KCl + 0.5 M KNO₃ + 0.1 M HNO₃) solutions has been determined at 25°C. SCC susceptibility was evaluated by slow strain rate tests (SSRT), at a strain rate of 1 × 10⁻⁶ s⁻¹.Welds obtained by FSW technique showed a higher corrosion resistance in EXCO solution and a lower pitting tendency than the base alloy. Electrochemical measurements (corrosion potential measurements, polarization curves recording) evidenced that FSW weld was cathodic to base alloy. FSW joints were not susceptible to SCC in both test solutions, whereas MIG joints cracked in both solutions.     

Evaluation of joint performance of 5056 aluminium alloy friction welded joints by heat input. On the tensile strength of welded joints (1st report)

Ferritic stainless steel SUS430 sheets were friction stir welded by using a Ni-base dual two-phase intermetallic alloy tool. After friction stir welding (FSW), the SUS430 work and the tools were evaluated in terms of microstructure and mechanical properties. The tensile specimens cut from the welded joints fractured in the base metal portion and their fracture strength was equal to that of the base metal. The stir zone comprised of recrystallized fine microstructure was observed, and also the thermo-mechanically affected zone was observed in an advanced side. Hardness in the upper one-third layer of the welded cross section was higher than the base metal. The admixture matter from work to tool surface occurred whereas that from tool to work surface did not take place in the scanning electron microscopy-EPMA resolution level. The amount of wear of tool was negligibly small, suggesting that the Ni-base dual two-phase intermetallic alloy is promising as a new type of FSW tool used for high melting materials such as steel.     

异种铝合金摩擦塞补焊工艺与组织性能

采用顶锻式摩擦塞补焊方法,以2219-T6铝合金为塞棒材料,分别对8 mm厚2024-T3和7075-T6两种铝合金FSW接头进行了摩擦塞补焊试验研究,深入探讨了不同焊接压力下塞补焊接头的微观组织、显微硬度、力学性能及断口形貌特征. 结果表明,塞棒和母材或FSW焊缝是由等轴晶进行过渡,获得了紧密结合的接头,热力影响区和热影响区晶粒发生长大. 整个塞补焊接头塞棒区软化最严重,硬度在85 ~ 95 HV之间. 2024铝合金塞补焊接头抗拉强度和断后伸长率分别达到了母材的70%和65%以上,7075铝合金塞补焊接头抗拉强度和断后伸长率分别达到了母材的62%和48%以上. 塞补焊接头断裂模式为韧性特征.     

5mm厚铝合金双面搅拌摩擦焊接

对5mm厚的1050-H24铝合金板材进行了双面搅拌摩擦焊接(FSW)，重点研究了接头的拉伸性能和断裂部位及其影响因素。研究结果表明，一次焊接参数、二次焊接参数和焊接方向对双面FSW接头的拉伸性能和断裂部位有不同程度的影响。一次焊接参数的影响较小，而二次焊接参数的影响显著并且存在最佳取值。同向焊接的接头强度较高且断在前进侧(AS)或后退侧(RS)，而异向焊接的接头强度较低且只断在AS。在文中的试验条件下，1500r／min的旋转速度、400mm／min的二次焊速和同向焊接方式是最佳的工艺组合，接头最高强度达到母材强度的78％。     

Fabrication of SiC_p/AA5083 composite via friction stir welding

Microstructure and mechanical properties of SiCp /AA5083 composite fabricated by friction stir welding (FSW) were investigated.The influence of the number of FSW passes on the distribution of SiC particles and mechanical properties in the joint was studied.After one pass,the SiC particles were entangled in the upper side of the stir zone (SZ).However,the particle distribution became more uniform after two passes due to the repeated stirring of the joint.As the SiC particles facilitate the grain refinement in the SZ by the pinning effect,the particle including region has much smaller grain size than the SZ without SiC particles.The SiCp /AA5083 composite region exhibits a Vickers hardness of HV90,which is much higher than the value of HV80 in the SZ produced by FSW without SiC particles.