Al6061 Sheet Research Articles

Zinc-based alloy rapid tooling for sheet metal forming reinforced by SLM steel inlays

Among the existing rapid and economical sheet metal–forming technologies, stamping with a press using soft tools, especially low-melting-point alloy dies, is one of the few methods that can meet the precision requirements in industrial fields such as automobile manufacturing. However, the usability of the method is limited by the low strength of the soft base. The current study proposes a new structure of zinc-based alloy dies for sheet metal forming, where the weak features of the die blocks, such as protruding edges, are reinforced by selective laser melting steel inlays imbedded during solid–liquid compound casting. A technical route for fabricating the new tools was developed, and a W-shaped part was formed using an SUS304 sheet with a thickness of 0.32 mm and an Al6061 sheet with a thickness of 1 mm to validate the concept. The experiment and simulation results proved that clearer localized features, such as a smaller radius, can be formed on the workpiece with the reinforcement of steel inlays, while the springback is smaller and the abrasion resistance of the tool is higher. This method can improve the forming quality and durability of traditional soft tools in a convenient and affordable way.

The effect of methods of surface treatment of metal elements on their surface free energy, with a view to the formation of polymer-metal hybrid elements

An analysis was made of methods of chemical surface treatment of metal elements made of DC04 steel and Al6061 alloy, for the formation of polymer–metal joints in injection molding technology. The surface characterization included determination of surface free energy (SFE) by the OWRK (Owens–Wendt–Rabel–Kaelble) method, and determination of its polar and dispersive components. Depending on the chemical treatment applied, the highest values of the polar constant for DC04 and Al6061 sheets were 26.4 and 39.2 mJ/m2, respectively, the highest values of the dispersion constant were 55.6 and 53.5 mJ/m2, respectively, for DC04 and Al6061 sheets. In the case of the surfaces of sheets made of the Al6061 alloy, the increase in the polar component value was most favorably influenced by the etching with 15% NaOH solution for 5 minutes, and the increase in the dispersive component – by the etching with 15% NaOH solution with the addition of thiourea for 2 minutes. In the case of the surface of DC04 sheets, the increase of the polar component was most favorably influenced by chemical cleaning for 10 minutes (in a solution with the composition: Na2CO3 50 g/mol, Na3PO4 × 12 H2O 50 g/mol, NaOH 50 g/mol). The highest value of the dispersive component of the surface DC04 sheets was obtained after etching with 15% HCl solution with the addition of thiourea for 5 minutes.

A Comparative Study on Stationary-Shoulder and Conventional Friction-Stir-Processed Al-6061 Alloy

Al-6061 sheets of 3 mm thickness were subjected to stationary-shoulder friction stir processing (S-FSP) and conventional friction stir processing (C-FSP) using similar processing parameters. The results showed that sound C-FSP samples could be obtained by all the selected parameters, while only high rotational (or low traverse) speed was suitable for S-FSP. The surface of S-FSP sample became smooth in comparison with C-FSP sample; moreover, the application of stationary-shoulder refined the grains further in the stir zone and inhibited the coarsening of precipitates in the heat-affected zone. For defect-free FSP samples, the tensile strength of S-FSP sample was a bit lower (about 10%) than that of C-FSP sample; however, the elongation of S-FSP sample increased due to the fine microstructures of fracture location.

Flow and friction behaviors of 6061 aluminum alloy at elevated temperatures and hot stamping of a B-pillar

The flow and friction behaviors of 6061 aluminum alloy (Al6061) at elevated temperatures were investigated to form a B-pillar by hot stamping with Al6061 sheets. The modified Arrhenius and Cowper–Symonds model were developed based on hot tensile tests at temperatures of 350–500 °C and strain rates of 0.01–1 s−1. The coefficients of friction (COF) at temperatures of 300–500 °C were also measured. The tribological test results show that the COF ranged from 0.95 to 1.05 with a loading force of 1 N and from 1.2 to 1.53 with a loading force of 10 N. Finally, hot stamping of a B-pillar using Al6061 sheets with different solution heat treatment temperatures and lubricants was conducted. Stamping experiments show that the B-pillar wrinkled badly and cracked in cold stamping with or without lubricants. The B-pillar also cracked in hot stamping without lubricants, but B-pillars without cracks could be obtained under lubricated conditions. Further finite element simulations with the implementation of Cowper–Symonds constitutive equation and the tested COF values (as references) were used to investigate the crack mechanisms that arise in hot stamping. Simulation results show that the crack was due to adverse friction and large temperature difference between the sidewall and rounded corners caused by non-uniform cooling. Lubrication not only reduces the friction to promote metal flow but also weakens the temperature difference. Thus, parts without cracks can be obtained.

Micro friction stir welding of ultra-thin Al-6061 sheets

The plunging depth of 0.05mm was optimum for joint formation of 0.5mm thick Al-6061 sheet by micro friction stir welding. Increasing rotational velocity from 1500rpm to 2000rpm was beneficial to sound surface formation, while the taper pin with three flats owned wider process window than the single taper pin. The minimum ratio of thickness reduction of 2% was attained, which enhanced the area of load bearing. The taper pin with three flats owing to the severe stirring actions resulted in the finer grain size, improving tensile property. The maximum tensile strength by the taper pin with three flats reached 217MPa, equivalent to 90% of base material.

Development of a partition panel of an Al6061 sheet metal part for the improvement of formability and mechanical properties by hot forming quenching

In this study, the hot forming quenching process was investigated to improve the deficiencies that arise in materials subjected to conventional cold stamping, such as low formability and undesirable mechanical properties. The hot forming quenching process was mainly discussed in terms of formability and mechanical properties in this study and was first evaluated by preliminary tests. To examine formability, an evaluation was conducted using hot-tensile and hemispherical-dome stretching tests at temperatures of 350°C and 450°C, respectively. In addition, the mechanical properties of the formed part were predicted using quench factor analysis, which was based on the cooling temperature during the die quenching process. These preliminary test results were then used to predict the formability and hardness of the partition panel of an automotive part, where the analytical results indicated high performance of the hot forming quenching process, in contrast to conventional forming. Finally, the hot forming quenching experiment of the partition panel was carried out to validate the predicted results and the obtained formability and hardness values were compared with conventional forming at room temperature using T4 and T6 heat-treated sheets. The analytical and experimental results indicate that the hot forming quenching process is a very effective method for obtaining desirable formability and mechanical properties in the forming of aluminum sheets.

An experimental study on the compressing process for joining Al6061 sheets

Mechanical clinching is suitable for joining lightweight sheet materials. However, the use of mechanical clinching may be restricted because of the exterior protrusion. In order to reduce the protrusion height, a compressing technology was investigated with experimental method in this paper. A pair of dies was used to compress the protrusion in a single stroke. The average tension-shearing strength of the compressed joint with a compressing force of 28kN was increased from 1231 to 1654N, and the average cross-tensile strength was increased from 953 to 1102N. As for the compressed joints, the main failure mode is neck fracture mode. The energy absorption values of the compressed joints with different compressing forces are all higher than those of the clinched joint in the failure process. Geometric characterization of the joint profile was analyzed in terms of interlock, neck thickness and protrusion height. The interlock and neck thickness were enlarged with the decrease of the protrusion height in the compressing process. The protrusion height of the compressed joint with a compressing force of 28kN was reduced from 1.62 to 0.94mm. The compressed joint can be used in the visible areas where a higher strength and a lower protrusion are needed.

Investigation of the height-reducing method for clinched joint with AL5052 and AL6061

The high protrusion on the clinched joint affects the appearance of the joint. A height-reducing method was investigated in the work to reduce the protrusion height. The clinched joint was produced with AL5052 sheet and AL6061 sheet. Flat dies were used to conduct the height-reducing process in the experiment. A rivet was used in the height-reducing process to control the material flow of the protrusion and increase the strength of the joint. The cross-tensile strength, tension-shearing strength and energy absorption were investigated in the study. The cross-tensile strength and tension-shearing strength of the joint can be increased by the height-reducing method. The neck thickness also can be enlarged with the reduction of the protrusion. The height-reduced joint can absorb more energy than the clinched joint in the failure process. The height-reducing method was effective for reducing the protrusion height and increasing the strength of the joint produced with different sheets.

Mechanical properties of the two-steps clinched joint with a clinch-rivet

In the present study, mechanical properties of the two-steps clinched joint with a clinch-rivet were investigated. The two-steps clinching method includes two steps, mechanical clinching and upsetting with a clinch-rivet. The protrusion of the joint was upset to reduce the protrusion height with different upsetting forces. This method contributed to increase the strength and reduce the protrusion height of the clinched joint. Extensible dies were used to perform the mechanical clinching process, and a pair of flat dies was used to perform the upsetting process. AL6061 sheets were used to carry out the experiment. The upsetting forces were set to 25, 30, 35, 40 and 45kN respectively to generate different two-steps clinched joints. Forming force, geometrical parameters, material flow and mechanical properties of the two-steps clinched joint were investigated by an experimental method. According to the achieved results, the cross-tension and tension-shearing strengths of the two-steps clinched joints with different upsetting forces were all higher than those of the conventional clinched joint. The strength of the two-steps clinched joint with an upsetting force of 35kN was the highest of all. The average cross-tension strength of the two-steps clinched joints with an upsetting force of 35kN was increased by 25% compared with the conventional clinched joints, while the average tension-shearing strength of the two-steps clinched joints was increased by 128%. The two-steps clinched joint could absorb more energy than the conventional clinched joint in the failure process. The two-steps clinching method was proved to be effective and reliable.

Numerical and experimental investigations of the reshaped joints with and without a rivet

Because of the high protrusion above the sheet, the mechanical clinching method might be restricted in some areas. Two new reshaping methods by compressing the protrusion with/without a rivet were investigated and compared in the current study. AL6061 sheets with the thickness of 2.0 mm were used in the study of the clinching and reshaping process. Extensible dies which consist of the punch, blank holder, die sectors, and anvil were used to generate the clinched joint, and a pair of flat dies was used to compress the protrusion in the reshaping process. A 2D model in the software DEFORM-2D was applied to analyze the strain and stress distribution of the reshaped joints with different protrusion heights. To validate the numerical model, experimental tests were carried out. Tension-shearing tests were carried out to obtain the tension-shearing strengths of the reshaped joints with/without a rivet. When the protrusion height was reduced to 1.0 mm, the tension-shearing strength of the reshaped joint reached the largest. The average tension-shearing strength of the reshaped joint without a rivet was increased from 1222.4 to 1247.3 N, and the average tension-shearing strength of the reshaped joint with a rivet was increased to 2756.6 N.

The experimental analysis of shear strength of round joints

Clinching technology is widely used in the automobile and furniture industries. Shearing strength is an important criterion for evaluating the quality of clinched joints. Round and rectangular clinched joints are based on the shape of the tools. In this article, the shearing strength of round joints was designed and discussed. Two methods, namely heat treatment and press-join orientation, were presented. Different rolling directions for Al6061, Al5052, and Q235 sheets were connected to investigate the shearing strength of round joints at 90° and 180°. An electric furnace was used to heat the clinched joints of the Al6061 sheets to 430 °C, 450 °C, 530 °C, and 570 °C and obtain the optimal heat treatment temperature. Results proved that press-join orientation and solid-solution treatment affect shearing strength.

Use of a modified Gurson model for the failure behaviour of the clinched joint on Al6061 sheet

ABSTRACTThis paper discusses the ductile fracture behaviour of the clinched joint on Alloy 6061 sheets. Failure behaviour of the clinched joint is associated with the nucleation, growth and coalescence of voids within the microstructure. Various corrections to the original Gurson model are proposed to allow for instability and final fracture of the material. This paper is concerned with the application of the modified Gurson–Tvergaard–Needleman damage developed by Ken Nahshon and Zhenyu Xue. The results of the tension tests are compared with those of numerical analysis to obtain the initial void volume fraction f0 and the shear damage coefficients kw. The modified Gurson–Tvergaard–Needleman model is used to describe the failure behaviour and the shear strength of the clinched joint. Good agreement is shown between the experiment results and the numerical results on the location of fracture and the maximum failure load.

Development of Accurate Numerical Models for Bending of Aluminum Tailored Blanks

Nowadays the main target in the automotive field is the realization of lightweight and safe components. In this way it is possible to reduce costs and improve fuel consumption and, at the same time, enhance passenger safety. The use of tailored blanks has increased considerably in the automotive industry. Tailored blanks are a combination of different thicknesses or different materials, obtained by welding together two or more blanks, used in particular in car body panels. A new requirement in the automotive sector is the application of aluminum tailored blanks. The main target of this paper is the development of accurate numerical models for bending tailored blanks made from thin aluminum sheets, joined by laser welding, without filler metal. The FE bending simulations have been carried out using an explicit solver. The accuracy of the numerical models has been estimated and improved through a comparison with the results from an experimental study. The experimental tests have been performed using bending testing equipment, designed and developed by the authors. Three different bending radii have been tested. Tailored blanks, used as specimens, have been made by laser welding of thin Al6061 sheets. The considered outputs, used for the numerical-experimental comparison, are the punch force and the bending angle. The experimental results have been compared with the numerical ones in order to verify the accuracy of the FE model related to thickness and radius variations.

Evaluation of properties and FEM Model of the Friction welded mild Steel-Al6061-Alumina

Evaluation of mechanical and interfacial properties of friction welded alumina-mild steel rods with the use of Al6061 sheet are presented in this work. SEM, EDX analysis, hardness and bending strength tests were conducted. The bonds were attained through interfacial interlocking and intermetalllic phase formation with average bending strengths in the range of 40 to 200 MPa and insignificant hardness change in the parent alumina and mild steel. A preliminary simulation was made to predict the deformation, stress, strain and temperature distribution during the joining operation using a fully coupled thermo-mechanical FE model. The aluminum alloy metal being rubbed was simulated using a phenomenological Johnson-Cook viscoplasticity material model, which suited for materials subjected to large strains, high strain rates and high temperatures. The highest stress, strain and deformation are found to be within the heat affected zone of the weld close to the periphery rubbing surface region and correspond to the highest temperature profiles observed.

Study of friction stir processing (FSP) and high pressure torsion (HPT) and their effect on mechanical properties

Production of Bulk Nano-structured Materials (BNM) using Severe Plastic Deformation (SPD) is currently being pursued by researchers all around the world. Recently FSP has gained prominence on account of its ability to create BNM in the processed specimen. In the present study an improvised Vertical Milling Machine is designed that can perform FSP on thin metallic sheets. Al6061 sheets of 2mm thick are subjected to FSP and its effect on microstructure is studied. It is observed that very fine grains are formed in these sheets. Further effect of FSP on hardness is studied with the help of micro hardness tester. It is found that the hardness has increased by 50% on the processed AL6061 sheets on account of FSP. The study clearly brings out the advantage of severe plastic deformation caused on account of FSP and HPT and is a step forward in developing Bulk Nano-structured Materials (BNM) materials in future. Another important SPD process is High Pressure Torsion (HPT). In this work Finite element (FE) modeling of HPT of a circular disc of commercially pure aluminum (Al99) is also attempted to illustrate the advantage using FEM in evaluating equivalent strain and hardness numerically prior to experimentation.

Investigations on forming of aluminum 5052 and 6061 sheet alloys at warm temperatures

In an ongoing quest to realize low-mass transportation vehicles with enhanced fuel efficiency, deformation characteristics of Al5052 and Al6061 were investigated. In the first part of this study, material behavior of Al5052 and Al6061 sheet alloys were investigated under different process (temperature and strain rate) and loading (uniaxial vs. biaxial) conditions experimentally. With the biaxial, hydraulic bulge tests, flow stress curves up to 60–70% strain levels were obtained whereas it was limited to ∼30% strain levels in tensile tests. The microstructure analysis showed that the change of grain size due to the effects of elevated temperatures and strain rates were not significant; therefore, it was concluded that the decrease in the flow stress at high temperature levels was mainly due to the thermally activated dislocation lines. In the second part, the effect of the temperature and the pressure on the formability was further investigated in a set of closed-die warm hydroforming experiments. The test results showed that a linearly increasing pressure profile up to ∼20 MPa levels did not have a significant effect on the die filling ratios and thinning of the parts when a uniform temperature distribution of 300 °C was applied. Finally, in the third part of the study, finite element models were developed for the same closed-die hydroforming geometry using the material behavior models obtained from bulge and tensile tests. Flow stress curves obtained from tests were compared in terms of predicting the cavity filling ratios and thinning profiles from the experiments. Based on the comparison, it was revealed that flow stress curves obtained from the warm hydraulic bulge tests provided accurate predictions at high strain levels (i.e., ε ¯ > 0.4 , when part filling is above 80%) while the flow stress curves from the tensile tests did so at low strain levels (i.e., ε ¯ < 0.2 , when cavity filling is below 80%). On the other hand, comparison of thinning values indicated that flow stress curves from bulge tests yielded good agreement with the experimentally measured values in general. Therefore, it can be recommended that the bulge test results should be used whenever available in order to conduct accurate numerical analyses for warm sheet hydroforming where complex geometry and loading conditions exist.