Alloy AA2024-T3 Research Articles

Development of mathematical model for friction stir welded joint using ‘R’ Programming

In Friction Stir Welding (FSW), the parent materials get fused and joined with each other without any addition of filler material. So in FSW, the weld joints have negligible weld defects in comparison to conventional fusion welding process. It is applicable to join both similar and dissimilar metals which is difficult in conventional welding processes. In the current study, FSW was carried out for AA 6061-T6 alloy using ‘General Full Factorial’ Design and measured the temperature distribution around the stirred zone. This paper describes the use of mathematical model for FSW joint of AA 6061-T6 using ‘R’ Programming to extrapolate the test findings. This mathematical model helps in correlating the process variables with the output response ‘Maximum Process Temperature’. The experimental values and the predicted values can be established by an empirical relationship. To assess the accuracy of the models developed for predicting the Maximum Process Temperature, Analysis of Variance (ANOVA) – F test and scatter diagram were applied.

Mechanism of residual stress and surface roughness of substrate on fatigue behavior of micro-arc oxidation coated AA7075-T6 alloy

The micro-arc oxidation (MAO) coatings were produced on AA7075-T6 alloy with a surface roughness (Ra) of 0.2, 0.8, and 1.6. The effects of the Ra of substrates on the morphologies of MAO coating and fatigue behavior of the coated samples were investigated. The structural characteristics of the MAO coating were analyzed by X-ray diffraction, scanning electron microscopy, and laser scanning confocal microscopy. Moreover, the residual stress in the oxide films was measured using an X-ray stress tester. The surface and cross-section analyses of the coatings revealed the mechanism of the oxide layer growth. The phase composition and the mechanism of residual stress were further investigated according to the heat transfer in the MAO process. The relationship between the nature of residual stress in MAO coating and the surface porosity as well as the temperature of the substrate and the coating was revealed. The fatigue test results showed a significant effect of the Ra of the substrate on the high cycle fatigue life at low cyclic stress levels. The residual stress relaxation attributed to the insignificant changes in the fatigue life of the coated samples with Ra = 0.2, 0.8, and 1.6 at high cyclic stress levels. Besides, the mechanism of the residual stress affecting the fatigue performance was explored.

Predicting the Wear Rate of Aluminum Alloy AA2024-T351 using Hybrid Linear function and Radial Basis Function

AA2024 is one of the heat treatable Al-Cu alloys with good strength to weight ratio and fracture resistance. It finds application mainly in aircraft and structural applications. In T351 tempered condition, AA2024 has improved hardness and strength. However, the softness of the matrix leads to high wear rate. In this study, tribological characteristics of AA2024-T351 is determined using a pin-on-disc tribometer by varying the sliding velocity, sliding distance and axial load as per face centered central composite design. A hybrid linear – radial basis function model is developed to explore the effect of normal load, sliding distance and sliding velocity on the wear rate of AA2024-T351 alloy. The predominant wear regimes in AA2024-T351 alloy is understood from the characterization study on the surface morphology of the worn specimens.

Dieless friction stir extrusion joining of aluminum alloy sheets with a pinless stir tool by controlling tool plunge depth

Abstract The present work explains dieless friction stir extrusion joining for aluminum alloy sheets, AA5052-H32 and AA6061-T6, of 2 mm thickness each. The joints are strengthened by metallurgical bonding as well as mechanical interlocking. The hook defect and the pinhole formation in friction stir spot welding are successfully eliminated in this new process. Experimental investigation of the effect of tool plunge depth on the formation of the joint and its performance is comprehensively discussed with mechanical performance tests, macro/ microstructuture analysis, hardness measurement, joint morphology and failure mode analysis. The joints possess shear fracture load of 7.7 kN, which is superior than that of friction stir spot welding and conventional friction stir forming. Higher tool plunge depth level ranging from 0.45–0.50 mm is found to be optimum choice for fabricating spot joints with better joint strength and aesthetic appearance. Slight increase in tool plunge depth yields significant improvement in the mechanical interlocking (collar growth). The zones identified through microstructural analysis, which are subjected to severe plastic deformation and frictional heat flux possess significant recrystallization and grain refinement. Reduction in hardness is observed over the joint spot than that of the parent metal. Morphological features of the joint are affected by increase in the plunge depth beyond the optimum range. The critical zones in the joint, which leads to pin failure and bonding delamination failure are also identified.

Effect of different machining parameters on surface roughness of aluminium alloys based on Si and Mg content

Aluminium-based alloys are considered lengthily for many applications in engineering areas due to their good mechanical properties. Machining these alloys had attracted the attention of many researchers on how to improve the machining, especially when high manufacturing rate is demanded. Usually, machining these materials poses some difficulties such as burr formation, roughness of the surface, continuous chip formation and build-up edge on cutting edge. In this study, AA6061T6, LM6 and AA5083 aluminium-based alloys were considered to research the optimum drilling parameters with the aim to address the earlier started challenges. Drillings were carried out by using a MAHO three-axis CNC drilling machine with an HSS drilling bit at three different spindle speeds and feed rates. From the results, it was established that each aluminium alloy has different surface roughnesses and this surface roughness decreases as spindle speeds increased. A minimum build-up edge was achieved for AA5083 and AA6061T6 alloys. However, a relatively high BUE was noticed in LM6.

Residual stress relaxation and duty cycle on high cycle fatigue life of micro-arc oxidation coated AA7075-T6 alloy

Ceramic coatings were produced on AA7075-T6 alloy by micro-arc oxidation (MAO). The MAO treatment was performed at different duty cycles (8, 10, 15, and 20%). Effects of duty cycle on microstructure and fatigue behavior of the coated samples were investigated. Surface features and cross-section morphology, and fatigue fracture were observed by SEM and laser microscope. Phase structure and residual stress in the coatings were analyzed by X-ray diffraction. The nature and relaxation mechanism of the residual stress were revealed. Finally, the influence of the residual stress relaxation on the fatigue life at high and low cyclic stresses was explored.

Electro chemical response of stir zone in friction stir welded AA7075-T651 joint in sodium chloride solution

Abstract High strength heat treatable aluminium alloy AA7075T-651 is widely used in aircraft industries. It is very difficult to weld in fusion technique due to poor solidification and microstructure in weld region. Friction Stir Welding is reliable technique to joining aluminium alloys in solid state condition with sound weld ability. In this work, rolled aluminium plate with thickness of 10 mm were square butt welded by Friction Stir Welding (FSW) process. The electrochemical corrosion behavior of FSW joints were investigated in 3.5% wt NaCl solution. The corrosion morphology of friction stir zone has been compared with parent metal. It is observed that, stir zone prone more corrosion potential than parent metal.

Crash-worthiness of a recently-developed AA 2624 aluminum alloy: Experimental studies

In this study, the crash-worthiness of a recently-developed AA 2624-T351 aluminum alloy plate was experimentally determined under dynamic compressive load along the normal (OP) and rolling (IP0) directions of the as-received plate. The alloy is characterized by anisotropic grain shape with an aspect ratio of 9:3:1 (RD:TD:ND). While IP0 specimens exhibit higher true strain and true strain-rate than those of the OP specimens, the latter exhibit higher dynamic impact strength than the former due to lower grain thickness of OP specimens (tOP) than that of IP0 specimens (tIP0). The strain-rate sensitivity, m, increased as deformation rate changed from the quasi-static (mOP = 0.0059 and mIP0 = 0.0023) to dynamic regimes (mOP = 0.25 and mIP0 = 0.19). At strain rates above 6070 s-1, the m value for IP0 specimens dropped significantly to -0.57 due to the formation of adiabatic shear band (ASB). While the deformation mechanism in AA 2624-T351 alloy is slip, the onset of dynamic fracture is preceded first by the saturation of <110>||CD fiber texture on the compression plane. This is followed by (a) the onset and exhaustion of slip bands (~7 μm thick), (b) onset and propagation of ASB, and (c) dynamic fracture along the ASB. These mechanisms hold for both OP and IP0 specimens but occur at a much lower impact momentum, true strain and true strain-rate in OP specimens due to their smaller grain thickness, tOP. This implies that the IP0 specimens exhibit better damage tolerance under dynamic impact loading than the OP specimens. Unlike the conical-shape ASB developed in equiaxed grained aluminum alloys, two unconnected, split ASB cone develops in AA 2624-T351 plate; a behavior that could open new ways of engineering the microstructure of alloys to resist ASB propagation. By comparison, the recently-developed AA 2624-T351 alloy has improved dynamic mechanical strength and better crash-worthiness than the more widely-used AA 2024-T351 alloy.

The Role of Lithium Salt Concentration in the Active Corrosion Protection of Aluminium Alloys

It has been demonstrated previously that lithium salts containing organic coatings offer effective active corrosion protection on AA2024-T3 alloys when exposed to neutral salt spray test for 168 hours [1, 2]. In the presence of a coating defect the lithium salts leach from the organic coating to the exposed metal substrate increasing the local pH to moderate alkaline conditions followed by the formation of a protective layer within the defect site [2, 3]. The lithium accumulation at the defect site and hence the formation of the protective layer is influenced by the inhibitor loading and solubility in the coating as well as the coating defect size. Three different surface compositions of the lithium protective layer have been recently identified as lithium-based layered double hydroxide (Li-LDH), lithium mixed pseudo-boehmite (Li-PB) and pseudo-boehmite (PB) each depending on the lithium leaching rate and the coating defect size [4]. For small defect sizes a high lithium concentration is hypothesized to result in the generation of Li-LDH. Furthermore, Li-PB is identified within moderate defect sizes and moderate inhibitor concentration and PB is generated within large defect sizes where low lithium concentrations are expected. On this basis, this paper describes the lithium active corrosion protection on aerospace aluminium alloys as a function of the inhibitor concentration. In doing so, commercial AA2198-T8 and AA2024-T3 aluminium alloys are immersed for 24 hours in lithium salt containing aqueous solutions at systematically varied lithium salts concentration from 10-6 M to 10-1 M. The alloys are then transferred to 10-1 M aqueous NaCl solution at near neutral pH conditions and either LPR measurements are performed as a function of time over 100 hours or anodic polarization is performed. The surface composition of the alloys after 24 hours immersion in lithium containing aqueous solution is also characterized. The surface composition and the electrochemical characteristics of each lithium passive layer generated is determined as a function of the lithium concentration. The surface composition of the passive layer ranges from PB to Li-PB and Li-LDH with increasing inhibitor concentration. The polarization resistance obtained as a function of time is correlated to the corrosion rate of each generated passive layer thus demonstrating the corrosion protection performance of Li-LDH, Li-PB and PB. The generation and corrosion protection performance of each passive layer is also demonstrated under relatively thin electrolyte layers mimicking the exposure of a coating defect and the leaching of lithium salt from the coating matrix under atmospheric conditions. Visser, P., et al., Study of the formation of a protective layer in a defect from lithium-leaching organic coatings. Progress in Organic Coatings, 2016. 99: p. 80-90.Visser, P., et al., Electrochemical Evaluation of Corrosion Inhibiting Layers Formed in a Defect from Lithium-Leaching Organic Coatings. Journal of The Electrochemical Society, 2017. 164(7): p. C396-C406.Visser, P., et al., Mechanism of Passive Layer Formation on AA2024-T3 from Alkaline Lithium Carbonate Solutions in the Presence of Sodium Chloride. Journal of The Electrochemical Society, 2018. 165(2): p. C60-C70.Visser, P., et al., The chemical throwing power of lithium-based inhibitors from organic coatings on AA2024-T3. Corrosion Science, 2019. 150: p. 194-206.

Friction stir welding of T-joints in dissimilar materials: Influence of tool geometry and materials properties

The aim of this work is to investigate the influence of the materials properties, process parameters and tool geometry on the formation of defects and mechanical strength of Friction Stir Welding (FSW) of dissimilar T joints. The 3 mm thick aluminium plates of AA5083-H111 and AA6082-T6 alloys were arranged in a T- geometry, using the AA6082 alloy as the skin or as the stringer. An additional 1 mm thick plate overlaps the skin to provide material to fill the fillets. Two tool geometries were analysed. The geometry of the variable section pin of the tool allied to the setup dies constrains the formation of two independent material pin driven flows whose morphology depends also on the processed base material properties. Thus, the formation of weld defects is greatly affected by the tool geometry, the materials and the process parameters. AA 5083 requires low tool rotation (w) and traverse (v) speeds but w/v ratio above 16 to avoid defects. The oxides in the nugget, produced for very high w/v ratio, reduce the mechanical strength of the welds. The welds with AA 5083 skin exhibit similar fatigue strength to those with AA 6082 as skin, although the latter alloy has higher fatigue strength than the former.

Metallurgical behavior and variation of vibro-acoustic signal during preheating assisted friction stir welding between AA6061-T6 and AA7075-T651 alloys

Abstract The present work investigated the effects of pin profiles (cylindrical and square), pin eccentricity (0.5 mm and 1 mm) in cylindrical tool and preheating (secondary heating) on metallurgical behavior, variation of vibro-acoustic signal pattern and joint strength during friction stir welding (FSW) between AA6061-T6 and AA7075-T651 alloys. The eccentric tool pins were observed to provide good flowability and intermixing between dissimilar metals, increased the size of stir zone, and the grains in stir zone were sufficiently finer with eccentric tool pin than concentric pin. The magnitude of vibro-acoustic signal increased when shoulder plunging started and drop in signal was noted when the tool shoulder reached its desired depth. The signal magnitude was noted to be higher in welding stage compared to tool plunging stage as the tool took in fresh material during tool movement along the weld path. Preheating the workpiece prior to pin plunging and during welding notably influenced the flow behavior and mixing pattern, and the grains in stir zone were slightly coarser than those in specimen without preheating. Significant reduction in the magnitude of the signal was also observed after preheating. Tensile and flexural strength of joints were also improved slightly when additional heating was employed.

Numerical Simulation for FSW Process at Welding Aluminium Alloy AA6082-T6

This paper presents the numerical simulation of the Friction stir welding (FSW) process obtained by using the DEFORM 3D software package. Numerical simulations are based on experimental research, welding of aluminum alloy AA6082-T6 by FSW method, which has the thickness of 7.8 mm. The aim of this paper is to determine the reliability of numerical simulations in the FSW process, which is followed by large deformations, where influential geometric and kinematic parameters are varied. Numerical research was done on the basis of the adopted five-phase orthogonal experimental plan with a variety of factors on two levels and repetition at the central point of the plan for four times. The parameters varied in the experiment are: Welding speed v mm/min, a rotation speed of tool ω rpm, angle of pin slopes α o, a diameter of the pin d mm, diameter of the shoulder D mm. During the performing of the FSW process, forces were measured in three normal directions: Axial force Fz, longitudinal force Fx and side force Fy, as well as the temperature in the adopted measuring positions of the workpiece. The experimental results obtained in this way were compared with the numerical experiment in the same adopted measuring positions, i.e., in the paper an analysis and comparison of the obtained experimental and numerical data of the measured forces and the generated temperature field were made.

Hard Anodizing of Aerospace AA7075-T6 Aluminum Alloy for Improving Surface Properties

In the current research work undertaken, an oxide film was grown by performing hard anodizing process on a pure aluminum layer deposited by PVD magnetron sputtering process on AA7075-T6 alloy. The corresponding tribo-mechanical properties were evaluated and compared with those of the base alloy. The dry sliding wear experiments were carried out to investigate wear resistance of anodized AA7075-T6 against the AISI SS316 counter-body by means of a reciprocating tribo-testing setup. The hardness of AA7075-T6 after the anodizing process exhibited an enhancement of about 1.94 times. Results revealed that the wear of anodized coating was exceptionally less when compared with the substrate. Based on morphology and chemistry changes of worn-out surfaces and debris, it was determined that severe abrasive and oxidative wear was the primary wear mechanism for AA7075-T6. The anodizing process increased the friction coefficient from 0.33 to 0.46 but reduced the wear severity by altering the wear mechanism into mild polishing and abrasion. Anodizing enhanced the wear resistance of AA7075-T6 to about three times, and the wear rate decreased to around 4.3 times.

Scanning Kelvin Probe Force Microscopy and Density Functional Theory Studies on the Surface Potential of the Intermetallics in AA7075-T6 Alloys

The surface potentials of Mg2Si and Al7Cu2Fe intermetallic particles in AA7075-T6 alloys were investigated by scanning Kelvin probe force microscopy (SKPFM) technique. The experimental surface potentials of Mg2Si and Al7Cu2Fe intermetallic particles relative to Al matrix were ranging from − 368 to − 265 mV and 480–500 mV, respectively. A theoretical method for assessing relative nobility of intermetallics in Al alloys was discussed through first principle calculation. The work functions and surface energies of Mg2Si and Al7Cu2Fe surfaces were calculated by using density functional theory (DFT) method. The results showed that work functions and surface energies of Mg2Si and Al7Cu2Fe intermetallics were influenced by the orientations of crystal face and terminal types. At the oxygen coverage of 1/4 ML and 1 ML, the theoretical surface potential differences between Mg2Si intermetallics and Al matrix were increased by 10–560 mV and 0–620 mV, while those between Al7Cu2Fe intermetallics and Al matrix were increased by 62–360 mV and 102–331 mV. For the adsorption of oxygen atom, theoretical surface potentials of Mg2Si and Al7Cu2Fe intermetallics relative to Al matrix had a close agreement with the experimental surface potentials. It was verified that DFT method was a valuable theoretical approach to assess the relative nobility of different phases in alloys.

Enhancement of weld strength of laser-welded joints of AA6061-T6 and TZM alloys via novel dual-laser warm laser shock peening

In this paper, an experimental study is presented on an investigation to improve the weld strength of laser-welded joints via post-processing by warm laser shock peening (wLSP). A dual-laser setup was utilized to simultaneously heat the sample to a prescribed temperature and to perform the wLSP process on the laser-welded joints of AA6061-T6 and TZM alloys. Joints in overlap and bead-on-plate configurations were created by laser welding by a high-power fiber laser and post-processed with wLSP. The tensile tests carried out on wLSP-processed AA6061-T6 samples demonstrate an enhancement in the strength by about 20% over as-welded samples and the ductility of samples processed by wLSP improved by 30% over as-welded samples. The bead-on-plate (BOP) welds of TZM alloy processed with wLSP demonstrated an enhancement in strength by about 30% and the lap welds processed with wLSP demonstrated an increase in the joint strength by 22%. Finite element analysis revealed that the depth and magnitude of compressive stresses imparted by wLSP were greater than room temperature laser shock peening (rtLSP), which contributed to the enhancement of the joint strength for processed samples.

Effect of Heat Treatment on Microstructure and mechanical hardness of aluminum alloy AA7075

The mechanical properties of high strength aluminum alloy AA7075 were greatly affected by heat treatment. This paper was intended to clarify the effect of heat treatment on the microstructure and the mechanical hardness of commercial alloy AA7075-T651. Heat treatment was performed at a variation temperature of 300, 400, 500, and 600°C for 1 h in a vacuum furnace followed by a water quench. The surface observation was done by using optical and electron microscopy and the mechanical hardness was measured by the Vickers Hardness test. The XRD result on as-received alloy revealed the precipitates in the alloy was MgZn2, Al7Cu2Fe, and Al2CuMg. The average hardness of the as-received alloy was 136 HV. The hardness became significantly lower (78.5 HV) after heat treatment at 400°C while heat treatment at others temperature gave hardness in the range 116-122 HV. Heat treatment induced grain growth and dissolution of metastable precipitates. Reduction in the number of MgZn2 and Fe-rich phase decreased the hardness significantly. Heat treatment above 400°C promoted segregation of fresh precipitates which enhanced the metal hardness again. The metallic grain size increased with heat treatment temperature. At 600°C, most of the precipitates were segregated along the equiaxed grain boundaries.

Corrosion Behaviour of Aluminum Alloy AA7075-T651

The present work investigates the corrosion behavior of a high strength aluminum alloy AA7075-T651 which is widely used in the aerospace industry. The alloy composed of Zn, Mg, and Cu as the main alloying elements. The T651 referred to a peak strength temper. X-ray diffraction (XRD) analysis detected MgZn2 as the second phase next to the Al matrix. The corrosion behavior of AA7075 was studied by conducting an immersion test in 30 g/l NaCl and 10 ml/l HCl solution at 35°C based on ASTM B597 for 8, 16, 24 h. The specimen was then characterized by an optical microscope and scanning electron microscope (SEM). The results showed that the specimen experienced a severe corrosion attack as a result of immersion test, as indicated by the change in the surface appearance, the development of surface roughness, as well as significant weight loss. The surface became remarkably rough and grain embrittlement following the metal grain boundaries occurred down to 150 µm depth. The near surface layer became disintegrate and easily detached from the surface after immersion 16 and 24 h. The results indicated that the alloy was sensitive to intergranular corrosion.

Post-Weld Heat Treatment Effects on Mechanical Properties and Microstructure of AA6061-T6 Butt Joints Made by Friction Stir Welding at Right Angle (RAFSW)

Friction stir welding (FSW) provides users with many advantages over fusion welding techniques. Nevertheless, it is not widely employed in current industry mainly due to high equipment costs and royalties. To overcome these issues, a low-cost FSW technique operated at a right angle, called RAFSW, has recently been developed by our research team. To make the RAFSW technique reliable for potential users, we are going to analyze the effect of various post-weld heat treatments (PWHT) on the mechanical and physical properties of the RAFSW joints. To this end, optimized process parameters are used to weld butt joints of an AA6061-T6 alloy. The joints were characterized using a tensile test, a micro-hardness test, and metallography techniques. The most efficient aging time was obtained for various aging temperatures. Moreover, it was found that artificial aging at 220 °C for 30 min could be used as a fast and cost-effective artificial aging PWHT for the industrial sector. In addition, the repeatability of the PWHTs were demonstrated by studying the effect of waiting time prior to the artificial aging. Finally, it was revealed that a single fast artificial aging process is more beneficial than solubilizing followed by an artificial aging process in terms of tensile properties, consumed time, and cost.

Study of the influence of the RRA thermal treatment and plasma nitriding on corrosion behavior of 7075-T6 aluminum alloy

Aluminum alloys are mainly used in aircraft's structural components, which present the fatigue process as a predominant failure mode. The fact that there are many airports in coastal regions makes the study of aluminum alloy corrosive processes relevant as localized corrosion causes adverse effects on mechanical properties of the material. Plasma nitriding is an alternative method of raising surface hardness, fatigue resistance, wear and corrosion of alloys, there is a trend to expand the applicability of the plasma nitriding process through utilization of new materials and nitriding of aluminum and its alloys would be of greatest interest. In order to improve the corrosion behavior of 7075-T6 aluminum alloy, this work evaluated and compared the effect of RRA thermal treatment and plasma nitriding on the corrosion behavior of AA7075-T6 alloy. The tests were performed in 3.5%wt NaCl solution at room temperature (~25 °C) and pH ~ 6. The linear potentiodynamic polarization study showed that RRA thermal treatment and plasma nitriding were effective in improving corrosion behavior in saline solution. The protective efficiency of plasma nitriding was 64.2% and RRA treatment was 18.4%. The corrosive process at the T6 condition was deeper and generalized, with a high concentration of corrosion pits. For the RRA condition, the process was less generalized and not so deep, while in the plasma nitrided condition it was more localized and superficial, preserving much of the exposed surface in the corrosion tests. These results can be considered very promising by indicating an increase in the useful life of this material. This directly implies a consequent reduction in the preventive maintenance costs of the industries that use this alloy, as replacing damaged parts that have been treated by the plasma assisted technique used in this study may be performed at longer time intervals than the alloy parts without any kind of treatment.

Electromagnetic expansion joining between tubular and flat sheet component

To join tubular and flat sheet components, this paper investigates an electromagnetic expansion joining (EMEJ) method, which combines tube expansion and electromagnetic forming (an emerging high-speed forming technique). To enable partial modification of the conductive coil, an assembly-type Bitter coil was utilized. The aluminum alloys AA6063-O and AA7075-T6 were selected for the tube and flat sheet joining targets, respectively. EMEJ tests were performed with several charging voltages: 5.7, 7.5, 9.2, and 11.1 kV. Three EMEJ mechanisms were revealed by numerical simulations: a geometrical constraint imposed by the bulging and flanging of the tube, an interference fit imposed by the residual stress, and an indenting phenomenon caused by impact with the flat sheet. Complete joining without any looseness was accomplished at charging voltages of 9.2 and 11.1 kV. Through pull-out testing, the connection strength was confirmed to be higher than the yield strength of the tube, as was predicted by the numerical simulation. As a result, the tube and flat sheet were successfully joined by EMEJ without additional connecting elements, and the feasibility of EMEJ as an advanced joining technique was verified.