Effect of welding parameters on the mechanical properties of AA2024 aluminium alloy joints welded by resistance seam welding

In this study, sheets of aluminium alloy 2024-T6 of 1?6 mm thickness were welded using the technique of resistance seam welding (RSEW) with different welding parameters. The peak load, energy absorption and failure mode obtained from tensile shear tests were used to describe the mechanical performance of seam welds. The results revealed that the increase in welding current and time and the decrease in electrode force increased tensile shear strength. The interfacial to pullout transition for the AA2024 seam welds occurred at a critical weld nugget (WN) diameter of 3?77 mm. In addition, a hardness evaluation was carried out in order to determine the effect of welding parameters on the welded joints and it was found that the developed heat affected the joint hardness.

Dans cette étude, on a soudé des feuilles d’alliage d’aluminium 2024-T6 de 1·6 mm d’épaisseur en utilisant la technique de soudage par résistance en ligne continue avec différents paramètres de soudage. On a utilisé la charge maximale, l’absorption d’énergie et le mode de défaillance obtenus à partir des essais de traction en cisaillement pour décrire le rendement mécanique des soudures en ligne continue. Les résultats ont révélé que l’augmentation du courant de soudage et de la durée ainsi que la diminution de la force de l’électrode augmentaient la résistance au cisaillement par traction. La transition de l’interface à l’arrachement des soudures en ligne continue de l’AA2024 se produisait à un diamètre critique du noyau de soudure de 3·77 mm. De plus, on a évalué la dureté afin de déterminer l’effet des paramètres de soudage sur les joints soudés. On a trouvé que la chaleur développée affectait la dureté du joint.     

Shear Strength of Reactive Resistance Welded Ti6Al4V Parts with the Use of Ni(V)/Al Multilayers

The Ti6Al4V/(Ni/Al)/Ti6Al4V joints were obtained through reactive resistance welding which takes advantage of electric current heating to initiate the rapid exothermic reaction of Ni(V)/Al multilayers and activate diffusion of elements across the Ni/Al-Ti6Al4V interfaces. Simulations of temperature distribution, carried out using COMSOL^® software, showed temperature gradient in the joint being a result of differences in resistivity of the Ti6Al4V alloy and the (Ni/Al)/Ti6Al4V interface. Shear tests revealed that extending duration of the process from 2 to 6 minutes helped to improve the shear strength from ~?240 to ~?335 MPa. The microstructure observations of the samples after those tests showed that de-cohesion of the joint occurred along the filler material/base material interface. A microcrack network characteristic for reacted Ni/Al foil with small ridges was found on the flat surfaces of fractured samples.     

Microstructure,Thermal, Thermo-mechanical and Fracture Analyses of Hybrid AA2024-SiC Alloy Composites

This research work aims to investigate the inter-correlation between microstructure, thermal (thermal conductivity, thermo-gravimetric analysis), thermo-mechanical (dynamic mechanical analysis) and fracture characteristics of hybrid AA2024-SiC alloy composites fabricated via semi-automatic stir-casting process, as per standard industrial practice. Silicon Carbide (SiC) particulates of varying amount (0–6 wt%; @ step of 2%) were used to reinforce master batch of AA2024 wrought alloy, Silicon Nitride (Si3N4) and graphite particulates. The thermal conductivity and storage-modulus magnitudes of alloy composites have shown diminishing trend with hard SiC reinforcing phase, while material stability, viscous modulus, damping factor and fracture toughness have shown significant improvement. Uniform dispersion and better interfacial adhesion between matrix–reinforcement were observed from metallographic examination. The XRD analysis identified the different phases of the hybrid alloy composites. The trends in variations of physical, mechanical and tribological properties were supported by microstructure analysis, thermal analysis, thermo-mechanical analysis and fracture analysis.     

Mechanical properties of alloy Ti–6Al–4V and of stainless steel 316L processed by selective laser melting: influence of out-of-equilibrium microstructures

Abstract

Ti–6Al–4V and stainless steel 316L have been processed by selective laser melting under similar conditions, and their microstructures and mechanical behaviours have been compared in details. Under the investigated conditions, Ti–6Al–4V exhibits a more complex behaviour than stainless steel 316L with respect to the occurrence of microstructural and mechanical anisotropy. Moreover, Ti–6Al–4V appears more sensitive to the build-up of internal stresses when compared with stainless steel 316L, whereas stainless steel 316L appears more prone to the formation of ‘lack of melting’ defects. This correlates nicely with the difference in thermal conductivity between the two materials. Thermal conductivity was shown to increase strongly with increasing temperature and the thermophysical properties appeared to be influenced by variations in the initial metallurgical state.     

Laser Keyhole Welding of Dissimilar Ti-6Al-4V Titanium Alloy to AZ31B Magnesium Alloy

Laser keyhole welding of Ti-6Al-4V titanium alloy to AZ31B magnesium alloy was developed, and the correlations of process parameters, joint properties, and bonding mechanism were studied. The results show that the offset from the laser beam center on AZ31B side to the edge of the weld seam plays a big role in the joint properties by changing the power density irradiated at the Ti–Mg initial interface. The optimal range of the offset is 0.3 to 0.4mm in the present study. Some lamellar and granular Ti-rich mixtures are observed in the fusion zone, which is formed by intermixing melted Ti-6Al-4V with liquid AZ31B. The maximum ultimate tensile strength of the joints reaches 266 MPa. Furthermore, the fracture surface consists of scraggly remaining weld metal and smooth Ti surface. The higher the failure strength, the smaller the proportion of smooth Ti surface to whole interface is. Finally, the bonding mechanism of the interfacial layer is summarized by the morphologies and test results of fracture surfaces.     

Modeling of the Effect of Temperature, Frequency, and Phase Transformations on the Viscoelastic Properties of AA 7075-T6 and AA 2024-T3 Aluminum Alloys

The viscoelastic response of commercial aluminum alloys 7075-T6 and 2024-T3 as a function of temperature is presented. Experimental data are obtained with a dynamic-mechanical analyzer (DMA) at different loading frequencies and compared with the available transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) data. The effect of successive microstructural transformations (particle precipitation and redissolution) is revealed. An analytical model is developed, which fits the mechanical response up to 573?K (300?°C). The model takes into account the concentration of Guinier-Preston Zones (GPZ) and metastable precipitates (???? in AA 7075-T6 and ????/S?? in AA 2024-T3), allowing us to determine the kinetic parameters of these transformations. The activation energies were previously obtained by several authors from DSC measurements and other techniques, showing considerable dispersion. The presented data, obtained with a completely different technique, allow us to reduce the uncertainty on these data and show the potential of DMA measurements in the study of microstructural transformations.     

Grain structure development and eutectic solidification of discontinuous magnesium borate whisker reinforced AA2024 matrix composite

Abstract

In the present research, the solidification behaviour of MBO whisker reinforced 2024 aluminium alloy matrix composite (MBO/AA2024) was studied by employing computer based thermal analysis, scanning electron microscopy and differential scanning calorimetry. The results show that the addition of MBO whiskers refines the grain structure in the matrix of the MBO/AA2024 composite. The nucleation of primary α-Al phase took place away from the whisker surfaces and started within the interstice of whiskers. The whiskers had almost no significant influence on the refinement of the eutectic phases.

Dans cette recherche, on a étudié le comportement de solidification du composite (MBO/AA2024) à matrice d’alliage d’aluminium 2024 renforcée par des barbes de MBO, au moyen de l’analyse thermique automatisée, de la microscopie électronique à balayage et de l’analyse calorimétrique à compensation de puissance. Les résultats montrent que l’addition de barbes de MBO affine la structure de grain dans la matrice du composite MBO/AA2024. La nucléation de la phase primaire α-A1 prenait place à l’écart des surfaces de la barbe et commençait à l’intérieur de l’interstice des barbes. Les barbes n’avaient presque pas d’influence sur l’affinement des phases de l’eutectique.     

Electrochemical Behavior of SLM Ti–6Al–4V Alloy After Long Time of Immersion in Lactic Acid Environment

Metallurgical and Materials Transactions A - The corrosion behavior of selective laser melted Ti–6Al–4V alloy (SLM Ti–6Al–4V) was assessed in 0.1 M lactic acid + 0.1 M NaCl...     

Effect of Nanosecond Laser-Textured Ablation on Performance of Ti6Al4V Alloy Prepared by Composite Nitriding Process

As a widely used orthopedic implant, titanium alloy will face the corrosion of body fluid in human body. In addition, the wear of implants and bones in human body will also reduce the service life of implants. To improve the wear resistance and corrosion resistance of biological titanium alloy, Ti6Al4V alloy was modified by plasma nitriding and plasma-enhanced chemical vapor deposition (PN + PECVD) composite process, and then samples were ablated by nanosecond laser to form a regular surface texture. The textured Ti6Al4V and PN + PECVD samples marked as Ti6Al4V-T and PN + PECVD-T samples. The microstructure and phase composition of the samples before and after modification were observed by scanning electron microscope (SEM), energy-dispersive spectrometer (EDS) and X-ray diffraction (XRD). It was found that after PN + PECVD process, a TiN film with a thickness of 2 μm was formed on the surface of Ti6Al4V. The surface texture of Ti6Al4V-T sample was regular, but the PN + PECVD-T sample texture was wide and shallow irregular after nanosecond laser ablation. The Ti–O and Ti–N–O non-stoichiometric compounds appeared on the samples after nanosecond laser ablation. Through the wear and electrochemical corrosion test in SBF, it was found that PN + PECVD sample had the best wear resistance and corrosion resistance. The wear resistance and corrosion resistance of Ti6Al4V-T and PN + PECVD-T samples were much better than that of Ti6Al4V substrate. The results show that, nitrogen oxides formed on the surface had higher microhardness and surface density, which was beneficial to improve the wear resistance and corrosion resistance of implants.

     

YAG激光焊接Be/Al合金的结晶组织分析

采用YAG激光焊接方法,通过控制激光束的能量密度和焊接速度,对铍铝两种几乎完全不相溶的金属进行了焊接并得到了良好的接头组织.焊缝和热影响区的显微组织为典型的铍铝共晶组织.     

Brazing of Ti-6Al-4V and niobium using three silver-base braze alloys

Evaluations of the (infrared)-brazed Ti-6Al-4V and niobium joints using three silver-base braze alloys have been extensively studied. According to the dynamic wetting angle measurement results, the niobium substrate cannot be effectively wetted by all three braze alloys. Because the dissolution of Ti-6Al-4V substrate causes transport of Ti into the molten braze, the molten braze dissolved with Ti can effectively wet the niobium substrate during brazing. For infrared-brazed Ti-6Al-4V/Ag/Nb joint, it is mainly comprised of the Ag-rich matrix. The TiAg reaction layer is observed at the interface between the braze and Ti-6Al-4V substrate. In contrast, Ti-rich, Ag-rich, and interfacial TiAg phases are found in the furnace-brazed specimen. The dominated Ti-rich phase in the joint is caused by enhanced dissolution between the molten braze and Ti-6Al-4V substrate. The infrared-brazed Ti-6Al-4V/72Ag-28Cu/Nb joint is mainly comprised of the Ag-rich matrix and Ag-Cu eutectic. With increasing the brazing temperature or time, the amount of Ag-Cu eutectic is decreased, and the interfacial Cu-Ti reaction layer(s) is increased. The infrared brazed joint has the highest average shear strength of 224.1 MPa. The averaged shear strength of the brazed joint is decreased with increasing brazing temperature or time, and its fracture location changes from the braze alloy into the interfacial reaction layer(s) due to excessive growth of the Cu-Ti intermetallics. The infrared-brazed Ti-6Al-4V/95Ag-5Al/Nb joint is composed of Ag-rich matrix and TiAl interfacial reaction layer. With increasing the brazing time, the amount of Ag-rich phase is greatly decreased, and the interfacial reaction layer becomes Ti₃Al due to enhanced dissolution of Ti-6Al-4V substrate into the molten braze. The average shear strength of the infrared-brazed joint is 172.8 MPa. Additionally, the existence of an interfacial Ti₃Al reaction layer significantly deteriorates the shear strength of the furnace-brazed specimen.     

Investigation on Metallurgical Structure and Mechanical Properties of Dissimilar Al 2024/Cu FSW T-joints

In this research, T-joining of AA2024-T4 and commercially pure copper were performed successfully using friction stir welding. Effect of welding parameters on metallurgical and mechanical characteristics of the joints was studied. For this purpose, tensile strength, microhardness, and macro- and microstructures of the joints were investigated. Also, the fracture surfaces were examined using XRD and SEM. The best results were obtained for the 1130 rpm rotation speed (ω) and 12 mm/min travel speed (v), with the UTS of 156 MPa (~70% of Cu strength). The microhardness test showed that TMAZ and base metal of Al side had the maximum hardness amounts (148 and 155 HV, respectively). Generally, increase in the ω²/v ratio caused the nugget zone and HAZ grain size to increase. The results revealed the formation of Al₂Cu and Al₄Cu₉ intermetallic compounds in the border zone of the joints. The fractography results showed the occurrence of cleavage fracture in all the samples.     

Global and Local Mechanical Properties of Autogenously Laser Welded Ti-6Al-4V

Ti-6Al-4V sheets, 3.2-mm in thickness, were butt welded using a continuous wave 4 kW Nd:YAG laser welding system. The effect of two main process parameters, laser power and welding speed, on the joint integrity was characterized in terms of the joint geometry, defects, microstructure, hardness, and tensile properties. In particular, a digital image correlation technique was used to determine the local tensile properties of the welds. It was determined that a wide range of heat inputs can be used to fully penetrate the Ti-6Al-4V butt joints during laser welding. At high laser power levels, however, significant defects such as underfill and porosity, can occur and cause marked degradation in the joint integrity and performance. At low welding speeds, however, significant porosity occurs due to its growth and the potential collapse of instable keyholes. Intermediate to relatively high levels of heat input allow maximization of the joint integrity and performance by limiting the underfill and porosity defects. In considering the effect of the two main defects on the joint integrity, the underfill defect was found to be more damaging to the mechanical performance of the weldment than the porosity. Specifically, it was determined that the maximum tolerable underfill depth for Ti-6Al-4V is approximately 6 pct of the workpiece thickness, which is slightly stricter than the value of 7 pct specified in AWS D17.1 for fusion welding in aerospace applications. Hence, employing optimized laser process parameters allows the underfill depth to be maintained within the tolerable limit (6 pct), which in turn prevents degradation in both the weld strength and ductility. To this end, the ability to maintain weld ductility in Ti-6Al-4V by means of applying a high energy density laser welding process presents a significant advantage over conventional arc welding for the assembly of aerospace components.     

Effect of Alclad Layer on Material Flow and Defect Formation in Friction-Stir-Welded 2024 Aluminum Alloy

The effect of the Alclad layer on material flow and defect formation during friction-stir welding (FSW) of 6.5-mm-thick 2024Al-T351 alloy plates was investigated. To characterize the material flow during FSW, different cross sections of the keyhole and “stop-action weld” were made for metallographic observations. It was found that the top Alclad assembled at the shoulder/workpiece interface, thereby weakening the material flow in the shoulder-driven zone and favoring the formation of void defect at high traveling speeds. The bottom Alclad layer extended into the weld at excess material flow state, which could be avoided at balanced material flow state. A conceptual model of material flow was proposed to describe the formation of the weld. It was indicated that a perfect FSW joint of Alclad 2024Al alloy without defect could be obtained at an optimum FSW condition.     

Four-point-bend fatigue of AA 2026 aluminum alloys

High-cycle fatigue tests were carried out on a newly developed high-strength AA 2026 Al alloy, which was in the form of extrusion bars with square and rectangular cross sections, using a self-aligning four-point-bend rig at room temperature, 15 Hz, and R = 0.1, in lab air. The fatigue strength of the square and rectangular bars was measured to be 85 and 90 pct of their yield strength, respectively, more than twice that of the predecessor to the 2026 alloy (the AA 2024 Al alloy). Fatigue cracks were found to be always initiated at large Θ′ (Al₇Cu₂(Fe,Mn)) particles and to propagate predominantly in a crystallographic mode in the AA 2026 alloy. The fatigue fractographies of the square and rectangular extrusion bars were found to be markedly different, due to their different grain structures (fibril and layered, respectively). Fracture steps on the crack face were found in both of these extrusion bars. Since the 2026 alloy was purer in terms of Fe and Si content, it contained much less coarse particles than in a 2024 alloy. This partially accounted for the superior fatigue strength of the 2026 alloy.     

Microstructural characterization of dissimilar friction stir welds between AA2219 and AA5083

Fusion welding of dissimilar aluminum alloys is very challenging. In the present work, Al-Cu alloy AA2219-T87 was friction stir welded to Al-Mg alloy AA5083-H321. Weld microstructures, hardness, and tensile properties were evaluated in as-welded condition. Microstructural studies revealed that the nugget region was primarily composed of alloy 2219, which was placed on the advancing side. No significant mixing of the two base materials in the nugget region was observed. Hardness studies revealed that the lowest hardness in the weldment occurred in the heat-affected zone on alloy 5083 side, where tensile failure were observed to take place. Tensile tests indicated a joint efficiency of around 90%, which is substantially higher than what can be achieved with conventional fusion welding. Overall, the results show that satisfactory butt welds can be produced between AA2219-T87 and Al-Mg alloy AA5083-H321 sheets using friction stir welding.     

The Effect of a Laser Beam on Chip Formation during Machining of Ti6Al4V Alloy

The effect of the laser beam on chip formation when machining Ti6Al4V alloy has been investigated at different cutting speeds and laser powers. The characteristics of the segmented chip produced by laser-assisted machining (LAM) in terms of the tooth depth and tooth spacing were strongly dependent on the cutting speed and laser power. Two types of segmented chip formation processes were observed, one at low and the other at high cutting speeds with a continuous chip occurring between these two types of segmented chips. The critical cutting speed at which the transition from the sharp, segmented chip to the continuous chip occurred increased with laser power. To obtain the continuous chip, plastic deformation at the shear zone to match the deformation strain introduced by the cutting tool is required. This can be achieved by laser heating the material in front of the cutting tool. A physical model is proposed to explain qualitatively the chip segmentation in conventional machining and the continuous chip transition at high cutting speed with the application of a laser beam.     

Distinguishing the influence of aluminium and vanadium additions on microstructural evolution and densification behaviour during the sintering of ti6Al,ti4V and ti6al4v

In this work, the influence of pure Al (Ti6Al) and V (Ti4?V) powder additions on the sintering behaviour of a coarse CP-Ti powder compact was investigated. Pure Al melts and spreads to form intermetallic layers at the CP-Ti surface, causing swelling and prevention of sintering and shrinkage below 1050°C. Ti4?V compacts do not swell and begin to sinter at 990°C. The sinter rate for both Ti4?V and Ti6Al are similar at 1200°C and higher than the CP-Ti compact alone. Aluminium melting distributes this element better than the dispersed V particles, leading to more rapid homogenisation. When both pure Al and V are present (Ti6Al4?V), the sintering rate at 1200°C is similar to that of Ti6Al and Ti4?V. However, swelling is increased and homogenisation is slower, resulting in a reduced sintering aid effect compared to Ti6Al and Ti4?V.     

SiC_P/2024Al铝基复合材料的腐蚀及防护

用电化学方法研究了 2 0 2 4Al和SiCP/2 0 2 4Al基复合材料在 3 5NaCl水溶液中的耐蚀性 ,用电化学阻抗技术对它们的硫酸阳极氧化膜的耐蚀性进行了研究 .结果表明 ,SiCP/2 0 2 4Al复合材料在3 5 %NaCl水溶液中比相应的基体金属有较大的腐蚀敏感性 .SiCP/2 0 2 4Al的阳极氧化膜具有良好的耐NaCl溶液腐蚀能力 ,但其耐蚀性不如 2 0 2 4Al合金的阳极氧化膜 ,这是由于氧化膜中SiC颗粒的存在破坏了氧化膜的完整性和均匀性所致