Microstructural modification and mechanical property improvement in friction stir zone of thixo-molded AE42 Mg alloy

Thixo-molded AE42 Mg alloy was friction stir welded, and the soundness of joints was evaluated, together with the microstructure evolution and mechanical properties in friction stir zones. According to X-ray radiography, the optimum FSW condition range of AE42 alloy exists between AZ61 and AZ31 alloys, and it seems that the optimum welding condition range increases with decreasing Al content in the Mg alloys. There are mainly two kinds of compounds in the thixo-molded AE42 alloy, and FSW has little influence on the grainy Al₁₀RE₂Mn₇ compound, but it has great influence on Al₁₁RE₃ phase, which is changed from lamellar eutectic to small particles after welding. Furthermore, the average diameter of Al₁₁RE₃ particles in SZ decreases with increasing the traveling speed at constant rotation speed due to less heat input. The hardness in SZ is higher than that in BM, and tensile strength and elongation are both improved after welding because the stirring refines and uniforms the microstructure and intermetallic compounds.     

The role of rotation speed on intermetallic compounds formation and mechanical behavior of friction stir welded brass/aluminum 1050 couple

In this paper, the intermetallic compounds formation during dissimilar friction stir welding of brass to aluminum 1050 and its effect on the mechanical behavior of joint were studied. Scanning Electron Microscopy (SEM), Energy dispersive spectroscopy analysis (EDS) and X-ray Diffraction analysis were used to characterize intermetallics. In addition, tensile tests and microhardness measurements were performed to evaluate mechanical properties. The results showed that utilizing rotation speeds higher than 400 rpm leads to gradual formation of intermetallic compounds in the stir zone and at the interface. CuAl₂ is the dominant compound in the composite structure of the stir zone, whereas four intermetallic bands are detected at the interface. From aluminum to brass, two middle layers were formed. Then, CuAl₂, Cu₉Al₄ and CuZn were detected. The increase in rotation speed is accompanied by thickening and development of interfacial intermetallic compounds. The optimum rotation speed of 450 rpm yielded a narrow interfacial intermetallic compound and a lamellar composite structure within the stir zone which enhances the tensile strength of the weld. On the other hand, further increase of rotation speed lowers the tensile strength of the weld which is accompanied by disappearance of lamellar composite structure, increment of weld defects and thickening of interfacial intermetallic layer.     

Formation of intermetallic compounds in Al and Mg alloy interface during friction stir spot welding

The spot welding of Al plate to Mg plate was produced by friction stir spot welding using various tool rotation speed and duration time of the tool to investigate the effects of the welding parameters on the reaction of Al and Mg alloy. The interface microstructure and phase were investigated using optical microscopy, scanning electron microscopy and X-ray diffraction. The mechanical properties of the joints are evaluated using tensile test. Experimental results show that intermetallic compounds were formed in the interface of the Al and Mg alloys. The thickness of intermetallic compounds layer increases with increasing tool rotation speed and duration time, and has a significant effect on the strengths of the joints. Heavy thickness of intermetallic compounds layer seriously deteriorates the mechanical properties of the joints. The intermetallic compounds layer mainly contains Al₃Mg₂ and Al₁₂Mg₁₇     

Preparation of bimetallic nano-composite by dissimilar friction stir welding of copper to aluminum alloy

Butt friction stir welding between pure copper and AA5754 alloy was carried out. Reinforcing SiC nano- particles were utilized in friction stir welded (FSW) joints to decline the harmful effects of intermetallic compounds. Tensile tests, micro-hardness experiments, scanning electron microscopy and X-ray diffraction analysis were applied to studying the properties of welded joints. The joints with a travel speed of 50 mm/min and a rotation speed of 1000 r/min showed the best results. The presence of nano-sized SiC particles reduced the grain size of aluminum and copper in the stir zone (SZ) from 38.3 and 12.4 μm to 12.9 and 5.1 μm, respectively. The tensile strength of the joint in the presence of reinforcing SiC nano-particles was ~240 MPa, which is ～90% of that for the aluminum base. Furthermore, the highest microhardness of the weld zone was significantly increased from HV 160 to HV 320 upon the addition of SiC nano-particles. The results also showed that raising the heat generation in FSW joints increased the amount of Al₄Cu₉ and Al₂Cu intermetallic compounds.     

Materials flow and phase transformation in friction stir welding of Al 6013/Mg

Material flow and phase transformation were studied at the interface of dissimilar joint between Al 6013 and Mg, produced by stir friction welding (FSW) experiments. Defect-free weld was obtained when aluminum and magnesium were placed in the advancing side and retreating side respectively and the tool was placed 1 mm off the weld centerline into the aluminum side. In order to understand the material flow during FSW, steel shots were implanted as indexes into the welding path. After welding, using X-ray images, secondary positions of the steel shots were evaluated. It was revealed that steel shots implanted in advancing side were penetrated from the advancing side into the retreating side, whereas the shots implanted in the retreating side remained in the retreating side, without penetrating into the advancing side. The welded specimens were also heat treated. The effects of heat treatment on the mechanical properties of the welds and the formation of new intermetallic layers were investigated. Two intermetallic compounds, Al₃Mg₂ and Al₁₂Mg₁₇, were formed sequentially at Al6013/Mg interface.     

Mechanical and microstructural behaviour of 2024–7075 aluminium alloy sheets joined by friction stir welding

The aim of the present work is to investigate on the mechanical and microstructural properties of dissimilar 2024 and 7075 aluminium sheets joined by friction stir welding (FSW). The two sheets, aligned with perpendicular rolling directions, have been successfully welded; successively, the welded sheets have been tested under tension at room temperature in order to analyse the mechanical response with respect to the parent materials. The fatigue endurance (S–N) curves of the welded joints have been achieved, since the fatigue behaviour of light welded sheets is the best performance indicator for a large part of industrial applications; a resonant electro-mechanical testing machine load and a constant load ratio R=σ_min/σ_max =0.1 have been used at a load frequency of about 75 Hz. The resulted microstructure due to the FSW process has been studied by employing optical and scanning electron microscopy either on ‘as welded’ specimens and on tested specimen after rupture occurred.     

Influence of tool material on mechanical and microstructural properties of friction stir welded 316L austenitic stainless steel butt joints

In the present research, the influence of friction stir welding (FSW) tool material on the mechanical and microstructural properties of friction stir (FS) welded 316L stainless steel butt joints is investigated. FS welds were produced using two different tungsten based FSW tools having identical tool shoulder and pin profiles. In both the cases, the FSW experimental runs were carried out using tool rotational speed of 600 rpm, welding speed of 45 mm/min, axial force of 11 kN and tool tilt angle of 1.5°. The results of the study show that the joints produced using the tungsten lanthanum oxide tool are having superior mechanical and microstructural properties when compared to the joints produced using tungsten heavy alloy tool. Furthermore, the tool degradation study by mass loss and photographic techniques suggests that the tungsten lanthanum oxide tool is more prone to degradation by plastic deformation, whereas the tungsten heavy alloy tool is more prone to degradation by wear.     

静轴肩辅助铝镁搅拌摩擦搭接接头的组织与性能

文中将静止轴肩技术应用到铝镁异种合金的搅拌摩擦搭接过程中,并分析了焊接速度对接头成形和力学性能的影响.结果表明,静止轴肩能够增强上下板之间的材料交换,焊后搅拌区呈较大的洋葱环形貌,其内部分布大量的金属间化合物;搭接面处发生良好的冶金结合.由于生成金属间化合物,洋葱环区域的显微硬度值明显高于接头其它区域.X射线衍射结果表明,金属间化合物的主要成分是Al₃Mg₂和Al₁₂Mg₁₇.接头的抗拉强度随着焊接速度的增加呈先上升后下降的趋势,最大值在焊接速度为40 mm/min时取得.     

Microstructure and mechanical properties of friction stir lap welded Mg/Al joint assisted by stationary shoulder

Using magnesium alloy as upper sheet, 3 mm-thick AZ31 magnesium alloy and 6061 aluminum alloy were joined using friction stir lap welding assisted by stationary shoulder. The effects of tool rotating speed on cross-sections, microstructure and mechanical properties of Mg/Al lap joints were mainly discussed. Results showed that stationary shoulder contributed to joint formation, by which stir zones (SZ) were characterized by big onion rings after welding. Because of the big forging force exerted by stationary shoulder, the upper region of hook was well bonded. SZ showed much higher hardness because of intermetallic compounds (IMCs). The bonding conditions at the base material (BM)/SZ interface at advancing side and the hook region played important roles on joint lap shear properties. The X-ray diffraction pattern analysis revealed that the main IMCs were Al₃Mg₂ and Al₁₂Mg₁₇.     

带状组织对铝/镁异种金属搅拌摩擦焊接头力学性能的影响

采用搅拌摩擦焊(FSW)对厚度为4 mm的6061铝合金与AZ31B镁合金进行不同工艺的平板对接试验. 采用光学显微镜(OM)、扫描电镜(SEM)、X射线衍射仪(XRD)及能谱仪(EDS)对接头进行微观组织观察,采用电子万能试验机对接头力学性能进行测试. 结果表明,在接头焊核区(WNZ)中存在着明显的带状组织,带状组织是由插入镁基体中的铝合金条以及弥散分布在条带上的金属间化合物(IMCs)组成;IMCs主要为Al₁₂Mg₁₇和Al₃Mg₂;铝/镁异种金属FSW接头裂纹形核和扩展均发生在带状组织内;焊接工艺影响带状组织形态和IMCs尺寸及数量;随着转速(n)的增加或焊接速度(v)的降低,带状组织呈弯曲状,长度相对较短且呈不连续分布;当转速(n)过高或焊接速度(v)过低时,带状组织变细,但IMCs数量增多且尺寸变大;铝/镁异种金属FSW接头强度主要取决于带状组织形态和IMCs尺寸及数量.     

搅拌针长度对搅拌摩擦搭接焊铝合金/钢异种材料接头组织性能的影响

通过搅拌摩擦搭接焊接6061铝合金/QP980钢异种材料,讨论了搅拌针长度（1.5和2.1 mm）对焊接接头组织和性能的影响。结果表明,6061铝合金/QP980钢搅拌摩擦搭接焊接头分为3层结构：上层为铝合金层,中间层为Fe、Al及金属间化合物混合层状结构,下层为钢层。其中,当搅拌针长2.1 mm时,铝合金层含有散落的钢碎片。在中间层检测到2种金属间化合物,靠近Al的深灰色层为Fe₄Al₁₃相,靠近钢的是Fe₂Al₅相。随着搅拌针长度的增加,接头的失效载荷从4 kN降低到3 kN。短探针焊接的接头在接合界面处断裂,而长探针焊接的接头在铝和钢的混合区断裂。孔洞缺陷和钢碎片是导致断裂位置发生变化的主要原因。此外,嵌入铝基体中的铁屑在变形过程中起应力集中和裂纹萌生的作用,降低了接头的力学性能。     

Influence of zinc on intermetallic compounds formed in friction stir welding of AA5754 aluminium alloy to galvanised ultra-high strength steel

In this study, lap joints between AA5754 and DP1000 ultra-high strength steels were produced by friction stir welding. In order to investigate the roles of zinc on intermetallic phase formation and joint properties, steel substrates were used, two being galvanised coated and one uncoated. Joint performance has been evaluated in term of maximum tensile shear loading. The effects of the process parameter, translational speed; chemical compositions; and intermetallic phase formation on the mechanical properties have been investigated. The results show that joints with a galvanised layer exhibit higher strength as compared to the non-coated steel. A thicker galvanised layer promotes the presence of zinc in the aluminium matrix, resulting in better joint properties. The level of zinc contents in the aluminium matrix depends on process temperature and material circulation characteristics. Two stable Al-rich intermetallic phases, Al₅Fe₂ and Al₁₃Fe₄, were detected at the interface regardless of the coating conditions.     

Effect of Intermetallic Compound Phases on the Mechanical Properties of the Dissimilar Al/Cu Friction Stir Welded Joints

Types and distribution of intermetallic compound phases and their effects on the mechanical properties of dissimilar Al/Cu friction stir welded joints were investigated. Three different rotation speeds of 1000, 1200 and 1400 rpm were used with two welding speeds of 20 and 50 mm/min. The results show that the microstructures inside the stir zone were greatly affected by the rotation speed. Complex layered structures that containing intermetallic compound phases such as CuAl₂, Al₄Cu₉ were formed in the stir zone. Their amount found to be increased with increasing rotation speed. However, the increasing of the rotation speed slightly lowered the hardness of the stir zone. Many sharp hardness peaks in the stir zones were found as a result of the intermetallic compounds formed, and the highest peaks of 420 Hv were observed at a rotation speed of 1400 rpm. The joints ultimate tensile strength reached a maximum value of 105 MPa at the rotation speed of 1200 rpm and travel speed of 20 mm/min with the joint efficiency ranged between 88 and 96% of the aluminum base metal. At the travel speed of 50 mm/min, the maximum value of the ultimate tensile strength was 96 MPa at rotation speed of 1400 rpm with the joint efficiency ranged between 79 and 90%. The fracture surfaces of tensile test specimens showed no evidence for the effect of the brittle intermetallic compounds in the stir zones on the tensile strength of the joints.     

Effect of Shoulder Size on Weld Properties of Dissimilar Metal Friction Stir Welds

This article reports a research study that shows the effect of shoulder diameter size on the resulting weld properties of dissimilar friction stir welds between 5754 aluminum alloy (AA) and C11000 copper (Cu). Welds were produced using three different shoulder diameter tools: 15, 18, and 25?mm by varying the rotational speed between 600 and 1200?rpm and the traverse speed between 50 and 300?mm/min to achieve the best result. Each parameter combination was chosen to represent different heat input conditions (low, intermediates and high). The welds were characterized through microstructural evaluation, tensile testing, microhardness measurements, x-ray diffraction analysis, and electrical resistivity. Microstructural evaluation of the welds revealed that the welds produced consisted of all the friction stir welding (FSW) microstructure zones with organized flow lines comprising mixture layers of aluminum (Al) and copper (Cu) at the Stir Zones. The average Ultimate Tensile Strength (UTS) of the welds considered ranged from 178 to 208?MPa. Higher Vickers microhardness values were measured at the joint interfaces of all the welds because of the presence of intermetallic compounds in these regions. The x-ray diffraction analysis revealed the presence of Al₄Cu₉ and Al₂Cu intermetallics at the interfacial regions, and low electrical resistivities were obtained at the joint interfaces. An optimized parameter setting for FSW of Al and Cu was obtained at the weld produced at 950?rpm and 50?mm/min with the 18-mm shoulder diameter tool.     

Friction stir welding of magnesium alloy AZ31B to aluminium alloy 5083

Abstract

A preliminary investigation has been carried out into the application of friction stir welding for joining a magnesium alloy to an aluminium alloy. The work has shown that liquation during the welding process can lead to the formation of a brittle intermetallic at the joint interface. This intermetallic has a microstructure composed of a divorced lamellar eutectic containing Al₁₂Mg₁₇ and magnesium. The formation of this microstructure and its influence on mechanical properties are discussed in terms of solidification theory.     

Al-Mg-Mn-Sc-Zr合金板材搅拌摩擦焊和氩弧焊焊接接头的对比

研究Al-Mg-Mn-Sc-Zr合金的焊接工艺和焊接接头组织和性能。采用搅拌摩擦焊（FSW）和氩弧焊（TIG）2种焊接工艺对该合金的热轧和冷轧-退火2种使用态板材进行焊接。采用比较研究的方法测定和研究焊接接头的力学性能和显微组织,利用光学显微镜和透射电子显微镜研究焊缝的显微组织和力学性能之间的关系。结果表明,与基材相比,Al-Mg-Mn-Sc-Zr合金的热轧和冷轧-退火板材的FSW和TIG焊接接头的强度均下降,但FSW焊接系数高于TIG焊接系数。这是因为FSW焊接接头焊核区亚结构强化的丧失和Al3（Sc,Zr）的析出强化作用的极少量丧失,而TIG焊焊接接头的软化主要原因是其形变强化的完全丧失和Al3（Sc,Zr）的析出强化作用的大部分丧失,且搅拌摩擦焊焊核区晶粒比TIG焊的焊缝区晶粒更细小。     

An investigation on metallurgical characteristics of tungsten based tool materials used in friction stir welding of naval grade high strength low alloy steels

A non-consumable tool is a vital requirement for friction stir welding (FSW) of high melting point alloys such as steel and titanium. In this investigation, an attempt was made to understand the pre-weld and post-weld microstructural characteristics of three tungsten based alloy FSW tools viz. 90%W, 95%W and 99%W. A naval grade high strength low alloy (HSLA) steel plates of 5 mm thickness were welded using the above tools with a tool rotational speed of 600 rpm and welding speed of 30 mm/min. Microstructural characteristics of the FSW tools, before and after welding, were analyzed using optical microscopy (OM) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). From this investigation, it is found that the tool made of 99% W doped with 1% La₂O₃ exhibited microstructural stability at elevated temperatures during FSW process.     

Mechanical Properties and Microstructure of TIG and FSW Joints of a New Al-Mg-Mn-Sc-Zr Alloy

A new Al-5.8%Mg-0.4%Mn-0.25%Sc-0.10%Zr (wt.%) alloy was successfully welded by tungsten inert gas (TIG) and friction stir welding (FSW) techniques, respectively. The mechanical properties and microstructure of the welded joints were investigated by microhardness measurements, tensile tests, and microscopy methods. The results show that the ultimate tensile strength, yield strength, and elongation to failure are 358, 234 MPa, and 27.6% for TIG welded joint, and 376, 245 MPa and 31.9% for FSW joint, respectively, showing high strength and superior ductility. The TIG welded joint fails in the heat-affected zone and the fracture of FSW joint is located in stirred zone. Al-Mg-Mn-Sc-Zr alloy is characterized by lots of dislocation tangles and secondary coherent Al₃(Sc,Zr) particles. The superior mechanical properties of the TIG and FSW joints are mainly derived from the Orowan strengthening and grain boundary strengthening caused by secondary coherent Al₃(Sc,Zr) nano-particles (20-40 nm). For new Al-Mg-Mn-Sc-Zr alloy, the positive effect from secondary Al₃(Sc, Zr) particles in the base metal can be better preserved in FSW joint than in TIG welded joint.     

Mechanical Properties and Welding Power of Friction Stirred AA2024-T35 Joints

This study is concerned with the effect of friction stir welding (FSW) parameters on the mechanical properties and the consumed welding power for AA2024-T35 joints. AA2024-T35 is friction stir welded at different welding speeds (16, 40, and 80 mm/min), rotation speed (900, 1120, and 1400 rpm), and two tool profiles (triangular and square). The welding power is measured and evaluated with two previously established models (O. Frigaad, O. Grong, and O.T. Midling, A Process Model for Friction Stir Welding of Age Hardening Aluminum Alloys, Metall. Mater. Trans. A, 2001, 32A, p 1189–1200; O.P. Heurtier, M.J. Jones, C. Desrayaud, J.H. Driver, F. Montheillet, and D. Allehaux, Mechanical and Thermal Modelling of Friction Stir Welding, J. Mater. Process. Technol., 2006, 171, p 348–357). The tool profile as well as the welding speed show significant effect on the microstructure especially at lower welding speeds. The increase of the welding speed improves the mechanical properties for both tool profiles whereas it has an insignificant effect on the welding power. The square profile produces better mechanical properties and consumed more power, at 40 mm/min, than the triangular one. Moreover, the welding speed showed a weak effect on the welding power, but the need of power increased with the increase of the rotation speed. The measured power is found to be in agreement with the computed one through a theoretical work established by Heurtier et al. (Mechanical and Thermal Modelling of Friction Stir Welding, J. Mater. Process. Technol., 2006, 171, p 348–357).     

Joining of Al 6061 alloy to AISI 1018 steel by combined effects of fusion and solid state welding

The joining of a 6-mm thickness Al 6061 to AISI 1018 steel has been performed by the combined effects of fusion and solid state welding. The process is derived from friction stir welding (FSW) but with an adjustable offset of the probe location with respect to the butt line. Metallographic studies by optical microscopy, electron probe microscopy, and the utilization of the X-ray diffraction technique have been conducted. It was found that the intermetallic phases Al₁₃Fe₄ and Al₅Fe₂ exist in the weld zone. The tool was significantly worn during welding and is broken after traveling 100 mm at a rotational speed of 917 rpm. The wear of the tool significantly affects the structure of the weld, and the tool breakage was detected by the incorporated acoustic emission (AE) sensors. It appears that the joining of an Al 6061 alloy to AISI 1018 steel with a sound heterogeneous weld microstructure is feasible using this process, and the tool breakage can be detected by the AE sensing technique.