Friction stir welding of V-1461 and V-1469 high strength aluminium–lithium alloys

The problems of the technology of friction stir welding (FSW) of new high-strength aluminium–titanium alloys V-1461 and V-1469 are discussed. The technical and economical advantages of the process are shown, the parameters are determined and the optimum FSW conditions resulting in high mechanical properties of the welded joint are proposed.     

Increasing the reliability of welded joints in high-strength V-1461 aluminium–lithium alloy

Filler materials for welding V-1461 alloy, ensuring high cracking resistance, corrosion resistance and mechanical properties, are selected. The results of tests of the welded joints in static tensile loading and bending and the impact toughness of the weld metal and low-cycle fatigue strength are presented. The experimental results show that the application of impact ultrasound treatment increases by an order of magnitude the values of low-cycle fatigue resistance of the welded joints as a result of the formation of the nanostructured surface layers. The level of residual stresses in welded joints is determined.     

Effect of backing runs on the properties of welded joints in aluminium–lithium alloys

The effect of the parameters backing runs and the composition of filler material on the properties of a welded joint and the heat-affected zone is investigated. It is shown that the porosity of the weld metal in the areas with backing runs depends strongly on the welding conditions, and when using Sv-1557 wire, the strength and plasticity are higher than those of the Sv-AMg6 wire.     

Properties and structure of friction stir welded joints in 1424 and V-1461 (Al–Li) alloys*

The effect of the friction stir welding (FSW) conditions on the structure of welded joint and mechanical properties of 1424 and V-1461 alloys is investigated. FSW is accompanied by the formation of a recrystallized fine-grain microstructure in the welded joint. It is shown that the increase of the heat input to the welded sheets does not increase the average grain size in the weld zone (the average grain size is 1.5–2.2 μm). The tensile strength of the welded joints depends on the welding conditions for both alloys. Special features of the microstructure formed in the zone of the welded joint are discussed and the effect of the microstructure on the mechanical properties of the welded joints and evolution under the effect of heat treatment after FSW are determined.     

Bending properties of friction stir welded joints – Studies on characteristics of friction stir welded joints in structural aluminum alloys (report 4)

The objective of this work is to determine the best parameters for brazing ceramic joints of pre-metallized Al₂O₃ with Ti by a plasma process using amorphous ribbons of Cu₄₉Ag₄₅Ce_x alloy as the addition metal. The alloys were prepared in an arc oven, and later processed by melt spinning, varying Cerium content by 4–6%. Brazing took place in a vacuum oven and the following variables were analysed: deposition time of the Ti film and temperature and brazing time, which were related to the flex resistance in three points of the brazed joint. A linear regression equation was obtained, and the interaction between these factors was verified. The metallized ceramic surfaces showed excellent uniformity and the brazed joints demonstrated very good adhesion, achieving flex resistance values of up to176.8 MPa.     

Effect of heat treatment of the mechanical properties and corrosion resistance of welded joints in high-strength aluminium–lithium alloys

Experimental results show that the maximum level of strength characteristics is obtained in complete heat treatment (quenching + artificial ageing) after welding. The heat treatment of friction stir welded joints results in the equalization of the structural heterogeneity and removal of softening in the heat-affected zone. Post-weld heat treatment conditions have almost no effect on the protective properties of non-metallic inorganic coatings. The susceptibility to intercrystalline corrosion (ICC) of welded joints with anodic oxide and chemical oxide coatings is also eliminated.     

Friction stir welding of V-1469 high strength aluminium–lithium alloy

The results of investigations of the effect of the technology for repairing defects, formed in friction stir welding of V-1469 aluminium alloy (secondary pass, manual argon-shielded arc welding), and of the effect of heat treatment on the mechanical properties and nature of failure of the welded joints are presented.     

Comparative study on fatigue properties of friction stir and MIG-pulse welded joints in 5083 Al-Mg alloy

The objective of this investigation was to compare the fatigue properties of friction stir welds with those of MIG-pulse welds. The 5083 Al-Mg alloy was welded by single pass friction stir welding（FSW） and double-sided MIG-pulse welding. The results show that friction stir（FS） welds have a better appearance than MIG-pulse welds for the lack of voids, cracks and distortions. Compared with the parent plate, FSW welds exhibit similar fine grains, while MIG-pulse welds display a different cast microstructure due to the high heat input and the addition of welding wire. The S-N curves of FSW and MIG-pulse joints show that the fatigue life of FS welds is 18 - 26 times longer than that of MIG-pulse welds under the stress ratio of 0.1 and the calculated fatigue characteristic values of each weld increase from 38.67 MPa for MIG-pulse welds to 53.59 MPa for FSW welds.     

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.     

Effect of process parameters on corrosion rate of friction stir welded aluminium SiC–Gr hybrid composites

Abstract

In the present study, the influence of processing parameters of friction stir welding on the corrosion rate of the welded joints of aluminium SiC–Gr hybrid composites was investigated. The experimental results indicate that the corrosion resistance of the welded joints increases at high welding (traverse) speed and/or low values of rotational speed. These variations occur as a result of the changes in the joint microstructure, where fine grains are developed as a consequence of a relatively low heat input and fast cooling to room temperature by ambient air associated with low rotational speed and/or high welding speeds. The mixed electrode theory is used to explain these variations of the corrosion rate, where the area ratio of cathode/anode for the galvanic couple between the aluminium metal matrix and the reinforcement constituents becomes small for fine grains. Thus, the corrosion resistance of the welded joints is increased.     

Microstructural characteristics and mechanical properties of Al–Mg–Si alloy self-reacting friction stir welded joints

The 5?mm thick Al–Mg–Si alloy was self-reacting friction stir welded using the specially designed tool at a constant rotation speed of 400?rev?min^?1 with various welding speeds. Defect-free welds were successfully obtained with welding speeds ranging from 150 to 350?mm?min^?1, while pore defects were formed in the weld nugget zone (WNZ) at a welding speed of 450?mm?min^?1. Band patterns were observed at the advancing side of WNZ. Grain size and distribution of the precipitated phase in different regions of the joints varied depending on the welding speed. The hardness of the weld was obviously lower than that of the base metal, and the lowest hardness location was in the heat affected zone (HAZ). Results of transverse tensile tests indicated that the defective joint fractured in the WNZ with the lowest tensile strength, while the fracture location of the defect-free joints changed to the HAZ.     

Mechanical properties of friction stir welded joints of 1050 – H24 aluminium alloy

Abstract

The friction stir welding (FSW) of 1050 - H24 aluminium alloy was performed to investigate the mechanical properties of the joints and determine the optimum FSW parameters. The mechanical properties of the joints were evaluated via tensile tests. The experimental results showed that a distinct softened region located at the weld and heat affected zones occurred in the joints. The degree of softening and tensile properties of the joints are significantly affected by the welding process parameters, such as welding speed and rotation speed. The optimum FSW parameters can be determined from the relations between the tensile properties and the welding parameters, and the maximum tensile strength of the joints is equivalent to 80% of that of the base material. When the welding parameters deviate from the optimum values, a crack like defect or significant softening is produced in the joints, thus the tensile properties of the joints deteriorate and the fracture locations of the joints change. All these results can be explained by the hardness distributions and welding defects in the joints.     

Microstructures and mechanical properties of friction stir welded joints of Zr–Ti alloy

Zirconium–titanium alloy joints were successfully produced by friction stir welding. Unlike the (α+β) dual phase microstructure in base metal, only the β phase existed in the region in which temperature exceeded the β transient point for the as welded joint. Accordingly, the hardness in these regions exhibited integral decrement and uniform distribution features. The thermal simulation further showed that hardness variation was mainly determined by phase composition. Microstructure development in the nugget zone was mainly governed by continuous dynamic recrystallisation. Satisfactory ultimate tensile strength and elongation equal to the base metal were achieved in the as welded joint. Tensile fracture occurred at the heat affected zone near the retreating side of the joint. The fracture surface of the joint exhibited a mixing feature with quasi-cleavage facets and small dimples.     

Stability of Y–Ti–O precipitates in friction stir welded nanostructured ferritic alloys

Abstract

Nanostructured ferritic alloys, which have complex microstructures consisting of ultrafine ferritic grains with a dispersion of stable oxide particles and nanoclusters, are promising materials for fuel cladding and structural applications in the next generation nuclear reactor. This study evaluates microstructure of friction stir welded nanostructured ferritic alloys using electron microscopy and atom probe tomography techniques. Atom probe tomography results revealed that nanoclusters are coarsened and inhomogeneously distributed in the stir zone and thermomechanically affected zone. Three hypotheses on coarsening of nanoclusters are presented. The hardness difference in different regions of friction stir weld has been explained.     

Comparing similar and dissimilar friction stir welds of 2017–6005A aluminium alloys

Abstract

Similar and dissimilar friction stir welds made of aluminium alloys 2017-T6 and 6005A-T6 are compared in terms of heat inputs, temperatures, material flow distributions and resulting local and overall tensile properties. Similar welds are systematically hotter and weaker than the dissimilar welds. Predictions of a three-dimensional finite element model of the tensile test transverse to the weldline are assessed towards local deformation fields measured by digital image correlation. Deformation systematically localises on the weakest heat affected zone, which is on the 6005A side in the dissimilar welds.     

Fabrication and performance evaluation of dissimilar magnesium–aluminium alloy multi-seam friction stir clad joints

This investigation is aimed to establish empirical relationships between continuous multi-seam friction stir cladding process parameters (i.e., rotational speed, welding speed and shoulder overlap ratio) and the quality characteristics (bond tensile strength, shear strength and corrosion) of dissimilar magnesium–aluminium alloy clad joints. The influence of considered process parameters on the clad properties was reported. Furthermore, multi-criterion optimization procedure was used to obtain ideal processing conditions, which can yield higher interface strength and lower corrosion rate of fabricated composite plate. Results indicate that, the aluminium-rich thin continuous layer, Mg-rich irregular shaped regions consists of Al₃Mg₂ and Al₁₂Mg₁₇ intermetallic compounds and nature of mechanical interlocking has great influence on the joint interface strength. On the other hand, the corrosion resistance of the clad joints is greatly affected by the amount of magnesium mixed with top aluminium sheet during friction stirring. Also, bend testing shows that, the cladded joints exhibit excellent ductility.     

Tensile properties and mechanical heterogeneity of friction stir welded joints of 2014 aluminum alloy

1 INTRODUCTIONFriction stir welding ( FSW) is a new andpromising welding process that can produce low-cost and high-quality joints of many alloys[1 7]becauseit does not need consumable filler materialsand can eli minate some welding defects such ascrack and porosity . In the FSW process , thewelding temperature is lower than that in thefusion welding, and the metal is in the plasticstate ,so many fusion welding defects can be avoi-ded. At present , more and more researches havebeen focu…