AA5754 Sheets Research Articles

Complexity-Based Analysis of the Effect of Forming Parameters on the Surface Finish of Workpiece in Single Point Incremental Forming (SPIF)

Nowadays, the manufacturing industry is focused on newer modern manufacturing methods, such as single point incremental forming (SPIF). The popularity of the SPIF process in the manufacturing industry is increasing due to its capability for rapid prototyping, forming complex geometry with simple steps, and customizing products for customers. This study investigates the effect of forming parameters (feed rate and step size) on the surface structure of the aluminum AA6061 sheet. We employ fractal theory to investigate the complexity of deformed surfaces. Accordingly, we study the relationship between the complexity and roughness of the deformed surface. The results show that the complexity and roughness of the deformed surface vary due to the changes in forming parameters. Fractal analysis can be further employed in other manufacturing processes to investigate the relation between the complexity and roughness of processed surfaces.

A Comparative Investigation of Conventional and Hammering-Assisted Incremental Sheet Forming Processes for AA1050 H14 Sheets

Incremental Sheet Forming (ISF) is emerging as one of the popular dieless forming processes for the small-sized batch production of sheet metal components. However, the parts formed by the ISF process suffer from poor surface finish, geometric inaccuracy, and non-uniform thinning, which leads to poor part characteristics. Hammering, on the other hand, plays an important role in relieving residual stresses, and thus enhances the material properties through a change in grain structure. A few studies based on shot peening, one of the types of hammering operation, revealed that shot peening can produce nanostructure surfaces with different characteristics. This paper introduces a novel process, named the Incremental Sheet Hammering (ISH) process, i.e., integration of incremental sheet forming (ISF) process and hammering to improve the efficacy of the ISF process. Controlled hammering in the ISF process causes an alternating motion at the tool-sheet interface in the local deformation zone. This motion leads to enhanced material flow and subsequent improvement in the surface finish. Typical toolpath strategies are incorporated to impart the tool movement. The mechanics of the process is further explored through explicit-dynamic numerical models and experimental investigations on 1 mm thick AA1050 sheets. The varying wall angle truncated cone (VWATC) and constant wall angle truncated cone (CWATC) test geometries are identified to compare the ISF and ISH processes. The results indicate that the formability is improved in terms of wall angle, forming depth and forming limits. Further, ISF and ISH processes are compared based on the numerical and experimental results. The indicative statistical analysis is performed which shows that the ISH process would lead to an overall 10.99% improvement in the quality of the parts primarily in the surface finish and forming forces.

Strength enhancement of AlMg sheet metal parts by rapid heating and subsequent cold die stamping of severely cold-rolled blanks

A trade-off between high strength and formability is forcing the automotive industry today to use several different aluminum alloys in structural assemblies. This leads to a reduced recyclability, which ultimately affects the sustainability of the entire product. In this work, it is demonstrated that a severely cold-worked AA5182 sheet metal blank can be formed to a sound part through a heat treatment of 10 s at 300 °C and a subsequent cold die forming. The high dislocation density in the as-received feedstock is induced by means of cold-rolling and promotes a yield strength of 326 MPa. The rapid heating with a heating rate of 24 K/s allows to increase the local ductility of the investigated material in a warm condition by more than 200% while preserving the initial grain structure of the material. Combined with additional work-hardening during forming, the final yield strength of the formed part is 319 MPa. The recovery kinetics of the as-received AA5182-H19 sheet are examined between 150 °C and 300 °C with dwell times between 1 s and 30 s. It is found that above 250 °C the fraction of residual strain hardening is a function of temperature and time. The resulting dislocation structures are investigated by a series of SEM, EBSD, and TEM measurements. Furthermore, the ductility enhancement is studied by a series of tensile tests with in-situ contact plate heating and fractographic analyses. Because the process under discussion allows to combine high strength and formability within one alloy, it is a promising approach to substitute 6000-series aluminum alloys in mixed-material assemblies and therefore make them easy to recycle.

Probing magnetic pulse welding of aluminium and steel sheets

Magnetic pulse welding is used to join overlapped thin sheets of dissimilar materials in solid state, which is not easy by fusion welding due to severe thermomechanical distortion and the formation of brittle intermetallic compounds. An intense electromagnetic pulse is employed that causes an impact between the overlapped parts leading to plastic deformation and rapid coalescence along the interface thereby posing a challenge to monitor the evolution of joint. An effort combining experimental investigation and numerical process modelling is presented here for a quantitative understanding of magnetic pulse welding of thin AA5754 and DC04 steel sheets with a flat linear coil of Cu-OFHC alloy. The numerical model couples an electromagnetic and a dynamic mechanical analysis to compute the transient electromagnetic pressure and the progressive impact between the parts and the plastic deformation that the parts experience for a given coil and sheet geometry and materials. The computed results of the impact velocity of the flyer on the target, the top and bottom part in the overlapped assembly, and the flyer–target contact length are examined against the corresponding experimentally measured results for several process conditions. The computed results are further used to elucidate the progressive nature of the evolution of the joint. Overall, the computational model has served as an important tool to uncover the underlying phenomena and identify suitable range of process conditions to produce a defect-free weld in magnetic pulse welding of sheets.

Characterization of galling during dry and lubricated punching of AA5754 sheet

When sheets of aluminum alloys are pierced or trimmed, tool failure occurs by the transfer of material from the sheet to the surface of the tool. This phenomenon referred to as galling adversely affects sheared edge quality and increases energy consumption. An instrumented pneumatic press was designed and built to conduct shear–punch tests on 2 mm-thick AA5754-O sheets and to investigate the progression of galling to AISI M2 steel punching tools during dry and lubricated punching. The punching tests were performed using a clearance of 2.0% of the lower die diameter. Cumulative galling volumes were measured using a non-contact optical surface profilometer, and the rate of material transfer (the galling rate) was estimated for both dry and lubricated punching. The galling initially occurred at a high rate, and for dry punching, it was reduced to 74.6×104μm3/stroke between 20th and 125th strokes. Lubricating the aluminum sheet with an oil-based lubricant mitigated the material transfer, and the galling rate after the 20th stroke was reduced to 3.1×104μm3/stroke. Punching force-displacement curves indicated a higher amount of energy expended to shear AA5754-O sheets in the dry punching compared to the lubricated punching that is suggested to be due to the higher galling resulting in higher friction forces at the interface.

Experimental and numerical studies on the formability of AA5754 and AA6082 thin sheets in nonisothermal warm redrawing process

The present work demonstrates a comparative investigation of the nonisothermal warm forward redrawing behavior of AA5754-H22 and AA6082-O sheets. The design and development of a new warm forward redrawing process was demonstrated. The complete redrawing was obtained by keeping the redrawing die and binder at 200 °C and cooling punch near to room temperature using water circulation. This process improved the thickness and surface strain distribution in redrawn cups without the onset of strain localization at the bottom corner. A thermomechanical finite element (FE) model of the nonisothermal warm redrawing process was developed applying the temperature-dependent Barlat-89 yield criterion and the Cowper–Symonds strain rate sensitive hardening model. The FE model reasonably predicted the part depth, earing development, thickness distribution, and surface strain evolution of the redrawn cups. The evolution of temperature distribution within the redrawing cup during the process was captured from FE simulations, and its role in the improvement in redrawing depth was demonstrated. Furthermore, the post-forming characterization of redrawn cup wall was also evaluated by microhardness and ring hoop tensile tests. It was found that the hardness, hoop tensile strength, and energy absorption capacity of AA5754-H22 cups were better than AA6082-O cups.

Investigation of microstructural and mechanical properties of AA1050-AZ91D dissimilar friction stir welding

Joining of aluminium and magnesium alloys frequently pose significant challenges to the extent where joining may seem impossible, due to differences in the physical, metallurgical, and chemical properties of the materials. Friction stir welding is a solid-state welding technique which uses a non-consumable tool to join metals. This study examines the dissimilar friction stir welding of 3 mm thick AA1050 and AZ91D alloy sheets. Successful defect-free joints were achieved at rotational speeds of 400 rpm and 600 rpm, and a constant traverse speed of 50 mm/min. The metallurgical investigations used to characterize the microstructure of the welds are optical microscopy (OM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The microstructures of the samples show distinct morphology attributed to their different rotational speeds. However, Al3Mg2 intermetallics (IMCs) phase was detected in the white bands present in both weld samples. The IMCs were formed through solid-state diffusion. The mechanical properties characterizations includes the microhardness profiles and tensile testing. The variation in the rotational speeds do not have a significant effect on the microhardness distribution of the weld samples. The tensile strength of the dissimilar weld improved substantially with the presence of an interpenetration feature (IPF).

Research on the material flow and joining performance of two-strokes flattening clinched joint

Clinching technology is widely used on thin-walled structures, but the joining of some special functional surfaces that require high strength is ignored by researchers. In the present work, a new joining technology suitable for functional surfaces, especially flat surfaces, called two-strokes flattening clinching (TFC), was introduced, which performs high-strength connections with a flat sheet surface. AA5052 sheets with thickness of 2.0 mm were adopted for experimental study of TFC process. The bottom dies are composed of the bottom ring, flap gaskets and anvil. AA5052 sheets are extruded by the punch into the bottom dies to form the initial clinched joint in the first stroke. The initial clinched joint is reverse stamped by different forces to form the TFC joint in the second stroke. The tension-shearing and cross-tension experiments were conducted to evaluate the mechanical performance of TFC joints. The material flow, static strength and energy absorption were investigated in this work. Furthermore, the relationship between neck thickness and interlock of the TFC joints under different flattening forces was studied. The result showed that the TFC joints have good mechanical performance. The tension-shearing and cross-tension strength reached 2951 N and 1646 N, respectively. The protrusion of joint disappears completely at a force of 35 kN, which means that the TFC process is able to join some functional surfaces and ensure good mechanical performance.

Formation of Heterogeneous Microstructure in AA1050/AA5052/AA6061/AA1050 Layered Sheet Processed by Cold Roll-Bonding and Subsequent Annealing.

A cold roll-bonding process was applied to fabricate an AA1050/AA6061/AA5052/AA1050 four-layer clad sheet and subsequently annealed. Three types of aluminum alloy sheets such as AA1050, AA6061 and AA5052 with 2 mm thickness, 40 mm width and 300 mm length were stacked up each other after such surface treatment as degreasing and wire brushing, then reduced to a thickness of 2 mm by multi-pass cold rolling. The rolling was performed at ambient temperature without lubricant using a 2-high mill with a roll diameter of 400 mm at rolling speed of 6.0 m/sec. The roll bonded AA1050/AA6061/AA5052/AA1050 clad sheet was then annealed for 0.5 h at 200~400 °C. Microstructures of the as-roll bonded and subsequently annealed aluminum sheets are investigated by electron back scatter diffraction (EBSD) measurement. After rolling, the roll-bonded AA1050/AA5052/AA6061/AA1050 sheet showed a typical deformation structure that the grains are largely elongated to the rolling direction. However, after annealing, it exhibits a very heterogeneous structure consisting of both deformation structure and recrystallization structure containing nanometer order grains. The formation of this heterogeneous structure and texture with annealing is investigated in detail through EBSD analysis.

Effect of Rotational Speed, and Dwell Time on the Mechanical Properties and Microstructure of Dissimilar AA5754 and AA7075-T651 Aluminum Sheet Alloys by Friction Stir Spot Welding

In the current study, the effects of dwell time and rotation speed on the mechanical properties and microstructure of friction stir spot welded joints of dissimilar aluminum sheet alloys were investigated. Aluminum AA5754 and AA7075-T651 alloys were selected as the work piece. The joint quality, microstructural evolution and mechanical behavior of the welded regions were considerably affected by the welding parameters. The results obtained that rotation speed and dwell time play an important role on welding quality of aluminum sheet. The microstructure images showed the dwell time and rotation speed has great effects on pin penetration and hook deformation. Maximum tensile shear load 806.3 N was produced at 1000 rpm and 2 s dwell time, while the tensile shear load reduced around 25 % with longer dwell time 5 s and high rotation speed 1400 rpm. Moreover, the welding joint microhardness was improved by the decrease of dwell time and increase of rotation speed.

Dissimilar friction stir lap welding of AA2198 and AA7075 sheets: forces, microstructure and mechanical properties

This paper investigates the dissimilar friction stir lap welding of AA2198 and AA7075 sheets. The influence of processing parameters, namely welding speed and tool rotational speed on joint features, microstructure, and mechanical properties were studied by implementing a full factorial design of experiments. Axial and transversal forces were continuously measured during the welding process using a sensed fixture aiming at the correlation of processing parameters, forces, and quality of the achieved joints. Obtained outcomes showed hook formation for all the combination of parameters and the existence of a very narrow processing window in which it is possible to avoid the formation of internal defects, such as grooves and tunnels. The influence of the weld bead morphology on the lap shear strength was elucidated proving that the strength is ruled by the hook morphology. The microstructure of the joints was studied and discussed considering also the microhardness distribution.Graphical abstract

High Strength-Elongation Balance in Warm Accumulative Roll Bonded AA1050 Sheets

High Strength-Elongation Balance in Warm Accumulative Roll Bonded AA1050 Sheets

Investigation on lightweight performance of tubular rivet-reinforced joints for joining AA5052 sheets

Investigation on lightweight performance of tubular rivet-reinforced joints for joining AA5052 sheets

Modeling continuous dynamic recrystallization of lightweight alloys by coupling polycrystal plasticity approach

In the thermo-mechanical process of lightweight alloys, such as aluminum alloys, complex microstructure evolutions are inevitably involved via the continuous dynamic recrystallization (CDRX) featured with extensive formation of subgrains followed by progressive transition into new grains. In this study, a novel fully integrated CDRX-VPSC (visco-plastic self-consistent) model is established. First, numerical formulations for formation and rotation of subgrains are addressed by reasonably tackling the grain boundary characteristics, and also the concept of generation for CDRX grains is newly introduced. By considering these two aspects, the grain population is updated according to the complex grain boundary evolutions. In the VPSC module of the integrated modeling, the shear strain rate, dislocation density, and orientation are calculated to update the grain populations and grain sizes in the CDRX module. The validation of the proposed model is conducted by simulating the hot compression of extruded AA7075 sheet, in which the DRX mechanism is controlled by the subgrain related dynamic recovery (DRV) and CDRX. The simulated flow stresses, microstructural evolutions (grains size and DRX fractions), and texture features agree well with reported experimental observations.

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.

Effect of plastic anisotropy and Portevin-Le Chatelier bands on hole-expansion in AA7075 sheets in -T6 and -W tempers

Influence of tempers on the hole-expansion formability of an AA7075 aluminum sheet is investigated for -T6 (as-received) and -W tempers (super saturated by the solution heat treatment followed by water quenching). The hole is prepared by end-milling, to limit the effects of hole preparation on the results and instead highlight the effects of material behavior. A flat-headed punch is used to expand the hole, and digital image correlation captures the strain fields throughout the experiment. The results present that the hole can expand by 70 % more in -W compared to -T6 temper with the lower forming force. In contrast, thickness strain distribution around the hole shows a similar pattern in both tempers except the observation of Portevin-Le Chatelier (PLC) effect in -W temper, which causing the inhomogeneous deformation. In parallel, the numerical simulation of the hole-expansion is performed using a user material subroutine implemented for the elasto-plastic material behavior, including plastic anisotropy, of both tempers. The predictions on the thickness strain variation and average level show good agreement with the experiment for -T6 temper, but less so for -W temper. This is shown to be the effect of PLC bands on the deformation: the material in -T6 temper is mainly governed by plastic anisotropy, but -W temper shows combined effect of plastic anisotropy and PLC bands. Nevertheless, the reasonable predictions of both tempers verify that the numerical framework established in this study can be used for preliminary, computationally-efficient virtual process design with a practical purpose, despite omitting the explicit physics of the PLC effect.

Mechanical Parameters Response on Micro-Friction Stir Welding of AA6061 and SS304 Sheets

Friction stir welding is a contact welding process that uses the heat generated by friction to fuse two different materials. This work is focused on the development of micro-friction stir welding which is carried out for very thin sectioned materials of thickness 1000[Formula: see text][Formula: see text]m or less. Friction welded butt-joints were successfully produced for 0.8[Formula: see text]mm thin AA6061 and SS304 sheets on a semi-automated vertical milling machine using a zero-pin length tool. A mild steel backing plate is used as fixture mechanism to hold the welding sheets on machine. Tool-rotational speed and Tool-travel speed are the weld-parameters examined on mechanical responses such as tensile behavior, micro-hardness and surface-roughness across the nugget-weld zone interface. The maximum tensile strength is obtained at lower weld-parameters. Tensile strength properties of AA6061-T6/SS304 joints were approximately found to be 25% lower than that of the AA6061-T6 alloy base metal. Maximum hardness value of 93HV and minimum roughness value of 2.808[Formula: see text][Formula: see text]m are observed for higher tool speeds at nugget-weld zone interface due to the formation of intermetallic phases. Microstructural behavior is studied on weld-parameters using scanning electron microscope and energy dispersive X-ray analyzer. Very thin intermetallic layers (consisting of Fe2Al5, FeAl3 and FeAl2 phases) were observed in stainless steel/aluminum interface.

Nonisothermal Warm Deep Drawing Behavior of Automotive Grade Aluminum Alloy Sheets

In this work, thermomechanical FE modeling of nonisothermal warm deep drawing of automotive grade AA5754 and AA6082 aluminum alloy sheets were performed. The deformable blanks were modeled using temperature dependent Cowper-Symonds constitutive equation along with Barlat-89 yield criterion. The predicted cup heights, earing, % thinning and surface strain distributions were successfully validated within acceptable error of 5%. The development of earing profile, cup thinning pattern and surface strains along 0°, 45° and 90° from rolling direction (RD) were plotted using the validated data. The ear profile developed in AA5754 cups was prominent compared to AA6082 due to relatively higher anisotropy at elevated temperatures. Thickening was more prominent along 45° to RD for AA5754, whereas thinning was higher in this direction for AA6082 material. The strain states developed at cup corner along plane strain condition was lower than the FLD0 values of materials. Thus there was uniform surface strains at cup corner indicating the improved ability of material to withstand more deformations. Comparatively, AA5754 exhibited relatively better formability compared to AA6082 material.

Assessment of different ductile damage models of AA5754 for cold forming

Aluminum alloys are characterized by low formability limits under cold forming conditions. The accurate prediction of deformation and failure in sheet metal forming allows for the optimization of forming process parameters and reduces tooling modifications and materials costs. Several models for ductile damage have been developed in the past decades to quantify and predict forming and damage response of sheet metal under complex-forming conditions. However, there is a need to identify a robust model which can provide realistic predictions for the behavior of aluminum sheet metal under the cold forming condition and different loading conditions. This work aims to investigate the prediction capabilities of different damage models for AA-5754 during the cold forming process. The experimental tensile and forming limit diagram (FLD) data of AA-5754 sheet metal used for the damage models’ calibration were obtained from literature. In this article, four damage models available in two broadly used the FE software; namely, LS-DYNA and PAM-STAMP were investigated. The models utilized from LS-DYNA material library were MAT_JOHNSON_COOK, MAT_GURSON, and MAT_GISSMO; while from the PAM-STAMP software, the novel CDM model was used. The cross-die formability tests for AA-5754 sheets were performed to validate these damage models. The predictions of the novel CDM model were found to give a good agreement with the experimental results obtained from the formability tests.

Dynamic recrystallization and solute precipitation during friction stir assisted incremental forming of AA2024 sheet

Friction stir assisted incremental sheet forming (FS-ISF) has been proved to further improve the formability of aluminum alloy sheets. Under such thermal forming condition, it is quite necessary to explore if the recrystallization and solute precipitation would happen, which might have potential in further improve the strength of aluminum alloy conventionally realized by heat treatment aging. In the present work, FS-ISF experiments are conducted for AA2024 sheet with proper parameters to achieve more solute precipitates and fine recrystallized grains with stable boundaries, of which microstructure evolutions are characterized by Transmission Electron Microscopy (TEM) and Electron Backscattered Diffraction (EBSD). It's found that cyclic and incremental plastic deformation during FS-ISF induces dislocation jogs and dislocation loops, and finally makes solute move into vacancies and generates solute precipitates. And friction stir also contributes to more solute precipitates than conventional incremental sheet forming (CISF) at room temperature. Meanwhile, precipitation zone inside grains helps to resist ductility damage and stable boundary with pinning contributes to higher strength. Besides, irregular sub-boundaries are merged and sub-boundaries consume dislocations to form new boundaries by the slip and arrangement of dislocations during dynamic recrystallization so that fine equiaxed grains with high angle boundaries are obtained, which results in higher yield strength (YS), ultimate tensile strength (UTS) and better ductility than those by CISF. Furthermore, investigations also demonstrate that static recrystallization cannot arise during FS-ISF.