Thin Aluminum Sheets Research Articles

Experimental and Numerical Analysis of Refill Friction Stir Spot Welding of Thin AA7075-T6 Sheets.

The refill friction stir spot welding (refill FSSW) process is a solid-state joining process to produce welds without a keyhole in spot joint configuration. This study presents a thermo-mechanical model of refill FSSW, validated on experimental thermal cycles for thin aluminium sheets of AA7075-T6. The temperatures in the weld centre and outside the welding zone at selected points were recorded using K-type thermocouples for more accurate validation of the thermo-mechanical model. A thermo-mechanical three-dimensional refill FSSW model was built using DEFORM-3D. The temperature results from the refill FSSW numerical model are in good agreement with the experimental results. Three-dimensional material flow during plunging and refilling stages is analysed in detail and compared to experimental microstructure and hardness results. The simulation results obtained from the refill FSSW model correspond well with the experimental results. The developed 3D numerical model is able to predict the thermal cycles, material flow, strain, and strain rates which are key factors for the identification and characterization of zones as well for determining joint quality.

Tool Downscaling Effects on the Friction Stir Spot Welding Process and Properties of Current-Carrying Welded Aluminum–Copper Joints for E-Mobility Applications

According to the technical breakthrough towards E-Mobility, current-carrying dissimilar joints between aluminum and copper are gaining an increasing relevance for the automotive industry and thus, coming into focus of many research activities. The joining of dissimilar material in general is well known to be a challenging task. Furthermore, the current-carrying joining components in E-Drive consist of pure aluminum and copper materials with relatively thin sheet thickness, which are thermally and mechanically very sensitive, as well as highly heat and electrically conductive. This results in additional challenges for the joining process. Due to their properties, friction stir welding and especially fiction stir spot welding (FSSW) using pinless tools—i.e., as hybrid friction diffusion bonding process (HFDB) is more and more attractive for new application fields and particularly promising for aluminum–copper joining tasks in E-Mobility. However, the feasibility is restricted because of the relatively high process forces required during friction stir welding. Thus, to fulfill the high process and quality requirements in this above-mentioned application field, further research and process development towards process force reduction are necessary. This work deals with the application of the tool downscaling strategy as a mean of process force reduction in FSSW of thin aluminum and copper sheets for current-carrying applications in E-Mobility, where the components are very sensitive to high mechanical loads. The tool downscaling approach enables constant weld quality in similar process time of about 0.5 s despite reduced process forces and torques. By reducing the tool diameter from 10 mm to 6 mm, the process force could be reduced by 36% and the torque by over 50%. Furthermore, a similar heat propagation behavior in the component is observable. These results provide a good basis for the joining of E-Drive components with thermal and mechanical sensitive sheet materials using the pinless FSSW process.

Effect of Fluid-Structure Interaction on Noise Generation in MAV with Fixed and Flapping Membrane Wing

An experimental study on the effect of fluid-structure interaction on noise generation in Micro Air Vehicle (MAV) with fixed and flapping membrane Tipula sp. wing is investigated. The acoustic performance of the fixed and flapping wing which made up of certain characteristic thin materials such as Low-density Polyethylene Terephthalate (PET), Thin Aluminium sheets (Al), and Non-woven fabrics (NWF) is analysed. An acoustic study is conducted to estimate the acoustic characteristic parameters of the insect mimic- membrane wing for various flapping conditions with various flapping frequency. In this research, the membrane wing with15cm of the total span is tested on both fixed and flapping MAV at different flexibility conditions and velocity conditions. The study of flapping MAV enables the study of the characteristic effects of sound emitted during the flapping motion of a wing. With the analysed results, the performance of wings is identified and compared with the sound pressure level. After analysing different materials, it is found that NWF produces 20% less noise than the other two more materials. Since the stiffness to strength ratio of metal is high, the formation of vortices is less compared to other membranes. For all fixed membrane wings at low Strouhal numbers, the formation of vortices is very low, and when the Strouhal number increases, the vortices became dense and results in the reduction of Sound pressure level.

Nano-alumina reinforcement on AA 8079 acquired from waste aluminium food containers for altering microhardness and wear resistance

The recycling of waste is act of charity as it takes part of maintain environmental clean as well as offer balance in supply to meet the same or alternate use. Thin Aluminium sheets made food packaging items are usually ‘use and through’ and AA 8079 obtained by recycled them after use by stir-casting process. This research aims to investigate the control over hardness and wear resistant by reinforcing alumina nanoparticles at different wt% in such recovered AA 8079 by Sliding wear test and Vickers micro hardness test to identify the degree of variation in mechanical and tribological aspect of reinforcement effects. The results of wear test reveal that the highly influencing functional parameter is normal pressure or load on the surface on the rate of wear than usage. The increase of quantity of reinforcement increases the wear rate in experimental results and the same confirmed with probability graph and the surface plots used to graphically analyses the relationship between combinations of parameters on wear rate. The increase of reinforcement increases, the microhardness also improved the same was depicted with microhardness graph. The effect of reinforcement in altering micro defects generation also investigated with SEM analysis and found that increase of reinforcement increases the micro defects. Contribution of wear functional factors and optimized parameter for minimum wear found by ANOVA and Taguchi analysis respectively. Hence the alteration of wear and microhardness properties can be done by nanoparticle reinforcement and the developed regression equation can be used for prediction of wear rate.

Experimental investigation on the effect of spot diameter on continuous-wave laser welding of copper and aluminum thin sheets for battery manufacturing

Welding of dissimilar materials, particularly copper and aluminum alloys, has gained considerable industrial interest in many different electric and electronic fields, such as the production of lithium-ion batteries for automotive applications. The differences in physical and chemical properties of these materials make fusion welding processes difficult to apply due to the formation of hard and brittle intermetallic compounds that impair both mechanical and electrical performance. In this paper, the effect of spot diameter on dissimilar laser autogenous lap-welding of copper and aluminum was studied. Experiments were conducted using a mid-power fiber laser source equipped with a galvo scanner and two different focal lengths to obtain two different spot diameters. The results showed that a smaller spot diameter promoted the formation of sound weld beads with better control of penetration depth, reduced mixing of the base metals and lower laser power requirements. By selecting the correct process parameters, good mechanical properties and low contact resistance could be obtained with both focal lengths. SEM-EDX analysis confirmed that a smaller spot diameter minimized the formation of copper rich phases in the weld bead.

Influence mechanism of the keyhole behavior on penetration depth by in-situ monitoring in pulsed laser welding of aluminum alloy

The dynamic behavior of keyhole plays a critical role in determining the weld penetration and process stability during pulsed laser welding of thin-sheet aluminum alloy. This study aimed to explore the influence mechanism of the keyhole instability on the penetration depth under different pulsed laser parameters. To this end, we firstly applied a high-speed camera to directly observe the oscillation characteristic of inner keyhole through a transparent glass, and its fluctuation period was nearly coincided with one pulse duration. Based on maximum deviation ratio, the pulse frequency has a more obvious effect on the fluctuation in keyhole depth comparing with laser power and focus distance. Along with the increase of laser power and frequency, the incident laser intensity also increased, which leads to an increasing of keyhole depth and decreasing of inclination angle. The weld penetration depth is determined primarily by the variation of the keyhole depth and inclination angle. The findings of this paper will provide theoretical basis for achieving the desired weld penetration and improving weld quality regarding keyhole formation.

Facing the Issues of Sheet Metal Equal‐Channel Angular Pressing: A Modified Approach Using Stacks to Produce Ultrafine‐Grained High Ductility AA5083 Sheets

A new approach for equal‐channel angular pressing (ECAP) of thin AA5083 sheets using two different orientations is investigated to address the issues of sheet metal ECAP. The method includes the deformation of a stack of 6 individual sheets supported by bulk material pieces placed on both sides of the stack. An excess length of the support materials and their pre‐deformation during an early stage of processing allows a buckling‐free deformation of the thin sheets for one of the investigated orientations. Multiple ECAP passes (up to N = 4) at room temperature following route C and microstructural analyses by electron back‐scatter diffraction are performed. Two passes of ECAP already result in considerable grain refinement with equiaxed grains, pronounced substructures and in an increased tensile strength at room temperature. At elevated temperatures (250 °C) a comparatively large elongation to failure (>130%) is found for the fine‐grained sheets. Diffusion‐controlled deformation mechanisms likely contribute to the deformation behavior of the investigated material. Scanning electron microscopy of the tensile specimens after testing reveals the formation of elongated and large cavities. These results highlight the suitability of the modified experimental method to produce (ultra)fine‐grained thin aluminum sheets with distinctly increased strength and ductility.

Ernest Rutherford’s ambitions

One of the pioneers of radioactivity research, Rutherford feared his work would be overlooked—and changed his publishing strategies to make sure it wasn’t.

Stress State of 3D-Printed Plastic Dies at Thin-Sheet Aluminum Bending

The paper deals with the problems and prospects of forming thin-sheet blanks, using ABS plastic dies, made by 3D printing. This technology combines the positive properties of plastic material and 3D-printing. The mechanical characteristics of the plastic were determined experimentally. On the basis of computer modeling, the dependence between the angle of bending the blank and the stresses arising in the dies is established. As a result of computer simulation and physical experiment, the value of the maximum thickness 0.5 mm for the aluminum 3003 blank is obtained. In this case, there is no plastic deformation of the plastic tool. The use of plastic dies does not require lubrication. The technology of sheet bending, using a plastic tool, can be implemented with the greatest efficiency in single and small-scale production.

Electromagnetic Embossing of Optical Microstructures with High Aspect Ratios in Thin Aluminum Sheets

Electromagnetic embossing enables the transfer of surface structures from forming dies to metal sheets at high forming speeds. For this purpose, the contactless forming force is provided by means of a magnetic field of a tool coil which interacts with an eddy current in the workpiece. In thin sheets which are completely penetrated by the magnetic field, the resulting Lorentz forces act as body forces that accelerate the workpiece onto the forming die. In addition to the body forces, also high strain rates can support the embossing of thin sheets. This investigation deals with the embossing of pyramidal structures in the submillimeter range and an aspect ratio of about 1 into thin aluminum sheets (3.0255 / Al99,5). In order to quantify the reproduced microstructures, their extent is determined by means of a lateral analysis. From this, the replicated height is derived. Up to now it has been possible to partially reproduce microstructures with a large aspect ratio in thin sheets. In addition, the changing surface roughness of the sheets is taken into account. Before embossing, the sheets exhibit a relatively rough surface with a rolled texture, which is smoothed by the impulse forming with an optical forming die. This study reveals basic approaches for the electromagnetic embossing of optical microstructures.

Analysis of Dual Semicircle Shape CSRR Sensor for Dent Detection on Teflon Coated Metal Surfaces

A planar microstrip transmission line with dual semicircle complementary split-ring resonator (CSRR) is proposed as a high sensitivity RF sensor for detecting non-uniformity of the surface of the thin metal plate. In automotive industries, a surface deformity on lightweight aluminum sheet components is a serious problem. Due to the uneven surfaces of the parts, typical flaws such as dents, dings, and waviness are not visible in the early stages of production. The defects, if ignored at an early stage, may lead to more production cost. So in this paper, we investigated the detection of flaws on the thin aluminum sheet under variable load conditions. The dual ring semicircle CSRR loaded microstrip transmission line implemented on Teflon (thickness = 0.08 mm) coated aluminum sheet (thickness = 3 mm) which behave as an RF sensor. By varying the depth of the dent from 1 to 2.05 mm on the aluminum sheet, the sensor was able to find the maximum frequency shift (nearly 800 MHz frequency) as compared to faultless (without a dent) aluminum sheet, in both simulations as well as in measurement conditions. As compared to circular shape CSRR, the dual ring semicircle CSRR has a high bonding effect between the electric field and metal sheet, which gives a more accurate prediction of dent portion on a thin metal sheet. This proposed compact RF sensor can be effectively utilized for crack avoidance in fiber optic glasses, crack avoidance in the gas pipeline, aircraft plate etc. By comparing frequency shift of the proposed CSRR sensor is more accurate, even invisible non-uniformities can be easily detected and thus can be prevented at an early stage to avoid any damage.

Fatigue life prediction of 2524‐T3 and 7075‐T62 thin‐sheet aluminium alloy with an initial impact dent under block spectrum loading

AbstractThis paper presents a fatigue life prediction model of post‐impacted sheets considering the effects of dent size and stress ratio. Low‐velocity impact tests at four different impact energies were performed on specimens cut from sheets of 2524‐T3 and 7075‐T62 aluminium alloy. Following the impact tests, static tensile and uni‐axial constant amplitude and block spectrum fatigue experiments were conducted. Numerical models were generated to determine the initial residual stress patterns, residual stress relaxation, and stress concentration factors around the impact dent. The S‐N curves and corresponding stress concentration factors and relaxed residual stresses of three of the post‐impacted specimens were used to determine the model parameters. Good agreement was achieved between the predictions and experimental results, and it has been demonstrated that the fatigue life prediction model can effectively simulate the effects of residual stress, stress concentration, and stress ratio on fatigue damage for post‐impacted thin sheet aluminium alloy materials.

The crack growth resistance behaviour of aluminium alloy 2024-T3 at slow strain rates after exposure to standard corrosive environments

SYNOPSIS The study investigates the effect of prior corrosive exposure on crack growth resistance behaviour of thin sheet (3 mm thick) aluminium alloy 2024-T3 at slow strain rates. Compact tension specimens were exposed to standard corrosive environments that simulate accelerated atmospheric corrosion attack. TWo corrosive environments were considered - an exfoliation corrosion (EXCO) solution and a 3.5 wt% sodium chloride solution. The unloading compliance R-curves of the two-hour EXCO-exposed specimens revealed a significant degradation of approximately 11% in the crack growth resistance behaviour (Kcevalues) compared to the baseline (air-exposed) values. Furthermore, secondary intergranular crack formation was also revealed in the plastic zone ahead of, and adjacent to, the crack tip of these specimens; which formed during the crack growth resistance loading. It is postulated that the observed degradation of the Kce values of the EXCO-exposed material is due to hydrogen embrittlement since the exposure times for the EXCO evaluation were limited to ensure that uniform corrosion dominated; that is, significant penetration of corrosion damage and pitting due to localized corrosive attack did not occur. The sodium chloride-exposed specimens revealed a similar degradation (13%) after 24 hours exposure. However, slight intergranular corrosive attack and isolated pitting were observed on the exposed surfaces prior to crack growth resistance loading, resulting in notch effects that could assist in crack growth. Pitting and intergranular corrosion were, however, not observed at the pre-crack tip. The relative contributions of the notch effects and the hydrogen embrittlement during the degradation of the KR performance are, therefore, unclear. Keywords: corrosion, crack growth, aluminium alloy 2024-T3.

A COMPARISON OF SERIAL AND PARALLEL SOLUTIONS OF TWO DIMENSIONAL HEAT CONDUCTION EQUATION

We study a comparison of serial and parallel solution of 2D-parabolic heat conduction equation using a Crank-Nicolson method with an Alternating Direction Implicit (ADI) scheme. The two-dimensional Heat equation is applied on a thin rectangular aluminum sheet. The forward difference formula is used for time and an averaged second order central difference formula for the derivatives in space to develop the Crank-Nicolson method. FORTRAN serial codes and parallel algorithms using OpenMP are used. Thomas tridigonal algorithm and parallel cyclic reduction methods are employed to solve the tridigonal matrix generated while solving heat equation. This paper emphasize on the run time of both algorithms and their difference. The results are compared and evaluated by creating GNU-plots (Command-line driven graphing utility).

Sharp Triple-Notched Ultra Wideband Antenna with Gain Augmentation Using FSS for Ground Penetrating Radar

A printed ultra-wideband antenna that provides wide bandwidth of 2.6–10.58 GHz, with sharp triple notches at 3.3–3.92, 5.1–5.4 and 5.68–6.02 GHz to eliminate the WiMAX and WLAN interferences, is proposed. Triple notches are implemented by embedding split ring shaped slot and unique circular split ring resonator pairs in the antenna. The antenna provides monopole like radiation patterns with gain variation of 2.5–5 dBi and average radiation efficiency of 86% in its pass band. Wide bandwidth of the antenna makes it well suited in low depth subsurface scanning ground penetrating radar (GPR) applications where better lateral resolution is desired. To improve the depth resolution, the antenna is integrated with reflective type frequency selective surfaces. Overall gain augmentation of 3 dBi with maximum gain increment of nearly 6 dBi at 5.5 GHz is achieved by adding the FSS. The antenna-FSS composite structure provides impedance band of 2.52–10.66 GHz with triple notches at 3.26–3.84, 5.1–5.38 and 5.66–5.95 GHz. Performance of the composite structure is evaluated in close proximity of sandy soil test bed by keeping thin aluminium sheet at the bottom of sand. Adequate VSWR, transfer function and group delay responses ensure the eligibility of proposed antenna to work for GPR.

Gain Augmentation of a Triple Notched Ultra-wideband Antenna using Compact Uniplanar Frequency Selective Surface for Ground Penetrating Radar

A simple structured, compact ultra-wideband (UWB) circular disk monopole antenna of dimension 35 × 30 × 0.8 mm3 that offers wide bandwidth from 2.64 to 9.36 GHz with sharp triple notch bands at 3.28–3.84, 5.08–5.44, and 5.62–6.06 GHz is integrated to the single-layer UWB frequency selective surface (FSS) that has unit cell dimension of 0.1136λL × 0.1136λL only where λL signifies the lower band-edge of UWB. Sharp triple notches are employed by embedding split-ring slot on circular patch and implanting dual circular split-ring resonator pairs at the backside of feed. Addition of FSS layer does not affect the antenna impedance band and offers significant antenna gain improvement by 2–4 dBi in the pass bandwidth with maximum gain of 8 dBi at 8.5 GHz. The antenna also provides high average radiation efficiency of 80%, improved radiation in the broadside direction and consistent group delay response in its pass band when integrated to the FSS layer. Working capability of proposed antenna-FSS structure is evaluated in proximity of soil test bed by keeping thin aluminum sheet at different buried levels. Adequate VSWR profile, linear transfer function response, and consistent group delay response in pass band ensure the eligibility of proposed antenna to work for ground penetrating radar.

Influence of Forming Parameters on the Mechanical Behavior of a Thin Aluminum Sheet Processed through Single Point Incremental Forming

Incremental sheet forming (ISF) is an economical process for batch production. This paper investigates post-forming mechanical properties with an emphasis on the relationship between residual stresses, strengths, micro-hardness and the strain-hardening exponent. Moreover, the influence of important process parameters on the post-forming tensile properties and hardness is analyzed. A Taguchi statistical analysis method is applied to study the effect of forming parameters and identify the best combinations to enhance the mechanical properties of the commercial aluminum. The results reveal that direct relationships exist for the plots of: (i) the strain-hardening exponent vs. the post-necking strain and (ii) difference of post-forming strengths vs. the strain-hardening exponent. Furthermore, the post-forming yield strength can be enhanced by 66.9% through the Single Point Incremental Forming (SPIF). Similarly, the ductility can be doubled by conducting the SPIF after performing the annealing of the as-received rolled sheet. In the present study, parts formed at a wall angle (θ) of 40° with a tool diameter (d) of 6 mm exhibit the highest strength. Moreover, most ductile parts will be obtained at ω = 1500 rpm, d = 22 mm and θ = 20°. It has also been shown that the compressive residual stresses are favorable for higher yield strength and improve hardness of the formed parts.

Pre-equilibrium stopping and charge capture in proton-irradiated aluminum sheets

We present a first-principles study of pre-equilibrium stopping power and projectile charge capture in thin aluminum sheets irradiated by 6 - 60 keV protons. Our time-dependent density functional theory calculations reveal enhanced stopping power compared to bulk aluminum, particularly near the entrance layers. We propose the additional excitation channel of surface plasma oscillations as the most plausible explanation for this behavior. We also introduce a novel technique to compute the orbital-resolved charge state of a proton projectile after transmission through the sheet. Our results provide insight into the dynamics of orbital occupations after the projectile exits the aluminum sheet and have important implications for advancing radiation hardness and focused-ion beam techniques, especially for few-layer materials.

Semi-analytical estimation of the effective plastic zone size at U-notch neighborhood in thin sheets under mixed mode I/II loading

In an effort to semi-analytically estimate the effective plastic zone size around U-shaped notches under mixed mode I/II loading by using the Tresca and Von-Mises yield criteria, explicit formulas of the elastic stress field at the neighborhood of such notches and the extended Irwin’s model are employed. Since the formulations are proposed under plane-stress conditions, they are useful to be used for thin sheets with elastic-plastic behavior. For verification of the proposed formulas, elastic-plastic finite element analyses are done on thin U-notched aluminum sheets and the corresponding numerical results are compared with the semi-analytical estimations. For the most cases, it is shown that the effective plastic zone size, which is crucial for determining the type of ductile failure, can be successfully estimated by using the proposed semi-analytical formulas. Furthermore, due to lack of precision of the analytical stress fields used in this study, the shapes of the plastic zones obtained by the semi-analytical and numerical methods are not the same. This research also reveals that instead of the complicated and time-consuming numerical elastic-plastic solutions, by using the semi-analytical method based on the linear elastic solution, the effective plastic zone size at the neighborhood of U-notches under mixed mode I/II loading can be determined simply and rapidly.

Investigating steel tool life in the RFSSW process

Abstract Refill Friction Stir Spot Welding (RFSSW) has demonstrated capability in joining thin sheets of aluminum with dissimilar thickness, alloy, and composition. The process remains to be implemented on a wide scale in the automotive and aerospace industries, partially due to the relatively short number of welds producible by a toolset, prior to needing cleaning. In the following work, an investigation was conducted to better understand this limitation. First, the effective tool life of a steel toolset was quantified. Experiments showed that less than 60 consecutive welds could be made before the toolset seized and required cleaning. To better understand the conditions contributing so such a short tool life, thermocouples were used in subsequent experiments, to measure the temperatures achieved at various locations in the weld. Peak weld temperature increased with longer cycle times and decreased with shorter cycle times. During the experiments, it was noted that weld temperatures in excess of 500 °C were observed at weld center. At these high temperatures, the authors anticipate that intermetallic compounds (IMCs) are able to grow on tool surfaces. A rough, existing model of IMC growth in an Fe-Al system predicted IMC growth on the same order of magnitude of the tool clearances, supporting the anticipation that IMC growth is a factor in the observed, short tool life between cleanings. Following this analysis, future evaluation of less re-active tool materials is recommended.