Superplastic Metal Research Articles

Finite Element Formulation and Computation of Superplastic Metal Forming Processes with Optimized Rate of Deformation Control

Superplastic forming (SPF) is a material forming technique that uses superplastic exceptional elongations and deformation characteristics to form superplastic materials into certain shapes. The combination of superplastic forming with diffusion bonding (SPF/DB) gives rise to an almost unlimited extension of superplastic forming since more integral lightweight cellular structural components can be manufactured. This paper discusses numerical modelling of the mechanism of superplasticity in metallic materials. The SPF computational method based on the finite element technique augmented with the controlling rate of deformations is developed to examine a range of design or operating conditions leading to more economical forming processes. The non-Newtonian ‘viscous flow’ material is used to model the constitutive of superplastic material during the forming period. The contact mechanics between the sheet material and the mold surface and the intersheet material contact mechanics are imposed using the penalty control method, in which the sticking contact boundary conditions are employed. The space discretization is carried out using the membrane element under plane strain and axisymmetric flow stress conditions, while the implicit time integration technique is utilized to follow the shape changes of the formed sheet material. The validation of the SPF finite element formulation was performed by comparing it with the available analytical solution of Hydraulic Free Bulging of Thin strips. The SPF of a hemispherical dome made of 7475 aluminum sheet alloy was performed to demonstrate the forming process as well as to validate the results obtained between the SPF finite element numerical simulation and the experimental results. The SPF/DB of the multicell component section is considered in the final part.

Formability Analysis on Superplastic Forming of AZ91 Magnesium Alloy Sheet

Superplastic sheet metal forming allows the production of complex parts that are not formable under normal conditions. Superplastic sheet metal forming processes are normally based on the same common principle: the sheet metal is firmly clamped between the die halves and is blow-formed by means of gas pressure. Generally superplastic forming can only be achieved in a very narrow range of strain rates and temperature. Superplastic materials are relatively stable when deformed; this behavior is related to the observation that the flow stress of a superplastic material is very sensitive to the rate of deformation. This paper aims to study the formability characteristic of Magnesium alloy by considering variable parameters, such as the sheet thickness, forming pressure and forming temperature. The forming time of 120 minutes is constant for the formability test. Keywards: Multi dome test, superplasticity, Mg – alloy, Thermomechanical processing, Formability.

Hot bend assisted gas forming of AA5083 sheet for making V-shaped trough containing deep uneven concavities

Employing low pressurized gas for shaping superplastic metal sheets into complex contours has long been adopted in the aero/auto industries and it is commonly recognized as superplastic forming (SPF). The most undesired feature of SPF would be an uneven thickness distribution in the final formed part. However, there are techniques that lessen this disadvantage. Low pressurized gas was used to make a V-shaped trough containing deep uneven concavities using superplastic AA5083. The auxiliary yet influential procedure of mechanically hot bending the flat sheet into a V-shape precedes the gas-forming process. In this first quick hot-bending operation, buckling will occur if the depth of bending exceeds a certain level. The degree of buckling and associated contours will affect the thickness distribution as well as the wrinkling location in the gas-formed product. A better thickness distribution is obtainable at the cost of wrinkle formation. Wrinkling can be purposely arranged to achieve better uniform thickness distribution, but it needs to be located outside the trim line of the gas-formed semi-product. Therefore, it is critical to manipulate the hot bending procedure to yield a suitable pre-form allowing a successful sequential gas-forming process.

Heat Assisted Dieless Drawing Process of Superplastic Metal Microtubes - From Zn22Al to β Titanium Alloys

A heat assisted superplastic dieless drawing process that requires no dies or tools is applied to the drawing of a Zn-22Al and β titanium superplastic alloy for not only circular but also noncircular microtubes such as square, rectangular and noncircular multi core tubes having square inner and rectangular outer cross sections. As a result, the tendency has been to increase the limiting reduction in area with increasing strain rate sensitivity index m value. We successfully fabricate Zn-22Al alloy, AZ31 magnesium, β titanium circular microtubes with outer diameter of 191μm, 890μm and 180μm, respectively. Furthermore, a noncircular micro tube, which has inner square tubes with a 335μm side, and an outer rectangular tube of 533×923μm were fabricated successfully. During the dieless drawing process, the geometrical similarity law in cross section which the tube is drawn while maintaining its initial shape can be satisfied. The smooth surface can be obtained in case of superplastic dieless drawing process without contact situation with dies and tools. Consequently, it is found that the superplastic dieless drawing is effective for the fabrication of circular and noncircular multicore microtubes.

Numerical Study of Radiation and Temperature Phenomena for Improved Super-Plastic Sheet Metal Forming

In most super-plastic forming (SPF) investigations the focus is usually on the material aspects. In this paper the authors develop a model to improve the heat management of SPF. The model presented improved process possibilities. The improved design involves selective application of heat to the material. Final product shape can easily be controlled by accurate temperature control of the work piece. Numerical simulation has been carried out on various components including a ‘top hat shape‘ and a heat exchanger part. Simulation comparisons are made between selective heating and conventional processing, where all of the formed material is at the same temperature, and greater process efficiency of the selective heating approach is demonstrated.

GILDING IN ARCHITECTURE

The application of a gold layer on the surface of a product - century tested way to improve the various properties of the processed materials. Gold plating is able to become a reliable protection against corrosion of metal or of the raid, as a result of contact with the environment. But the main cause that leads to conduct coating of gold is to increase the external decorative features of the products and to give them the uniqueness.The core of the gold has a large cross-section of neutron capture, the ability of the gold to the reflection of infrared rays is close to 100%, in the alloys it has a catalytic properties. Gold is very technologically easily produce ultrathin foil and micron wire. It is very ductile and superplastic metal, which can be shaped into various shades by adding other metals. Such a set of useful properties have served as the reason for the wide use of gold in architecture, which does not lose its relevance to this day.

Designing superplastic forming process of a developmental AA5456 using pneumatic bulge test experiments and FE-simulation

Relatively low tooling costs, high design complexity coupled with low forming speeds make the superplastic sheet metal forming process attractive, especially for smaller lot sizes. Due to the relatively small lot size, the effort and budget for designing superplastic forming processes is usually limited (Kappes and Liewald in J Mater Sci Eng B1:472–478, 2011). For this reason the tool design and corresponding pressure profiles in superplastic forming processes are often based on trial and error (Franchitti et al. in 11th international Esaform conference on material forming, 2008; Barnes in J Mater Eng Perform 4:440–454, 2007). Consequently a process chain should be established to design superplastic forming processes accurately and efficiently. This paper deals with the process chain to form an aluminium part superplastically. At the beginning of the process chain, there is a new, developmental aluminium alloy sheet (AA5456, s0 = 1.6 mm) designed for superplastic forming supplied by Hydro Aluminium Rolled Products GmbH. The relevant material parameters of this sheet are then determined via pneumatic bulge testing with and without in situ measurement of strains. Using these experimentally determined parameters superplastic forming process can be simulated by FE modelling (PAM-STAMP 2G). Due to in situ measurement of strains during pneumatic bulging, the comparison of experiment and FE-simulation results over the whole pneumatic bulging process could be done. This comparison shows good correlation for the observed conditions. Furthermore a cylindrical cup was simulated, evaluated via determined isobar Superplastic Forming Limit Curve (at fracture) and finally formed by pneumatic bulging. Material characterisation of the bottom of this cup showed that excessive cavitation was observed as a result of the iron-silicon particles. Superplastic forming of a bracket usually formed out of AA5083 was also simulated using material parameters of AA5456. The simulation was able to show that this part is not able to be manufactured out of AA5456 under these forming conditions, which was confirmed by forming trials performed at ALU-SPF AG.

Specific Mechanical Properties of Superplastically Formed Components and Resulting Applications for Vehicles

The technical requirements to produce parts as light as possible with more complex geometries are ever increasing in recent years in automotive industries, rail vehicle and aerospace. Manufacturing technologies such as super-plastic metal forming, which had been considered as a niche technology earlier, is now gaining greater technical relevance for industrial size production. The parts that have been generated through super-plastic forming in innovative vehicle for example Mercedes SLS AMG reflect the industrial activity in this area. Manufacturability of thin-walled structures enables lightweight design. Also the tool and manufacturing costs are lower in comparison. However, the main challenge could be found in maintaining exact process parameters. There is a large research potential in super-plastic forming; from the determination of optimal material data through process simulation to manufacturing of real parts and their characterization. In the framework of the project international Bureau of the Federal Ministry of Education and Research UKR005/08 “Manufacture of parts with special properties” a preliminary research work has been carried out.

Superplastic Forming of Combustion Chamber

The major advantage of superplastic forming (SPF) technology is that it can form integral and complex components in simple operation, since it is possible to form one or more sheets of superplastic grade metal into single surface tools by relatively low gas pressure. Duplex steel contains two phases in nearly equal proportions which can suppress grain growth at a high temperature, like superplastic Ti-6Al-4V, and many duplex stainless steels with fine grained microstructures show superplastic behavior. In this study, superplastic forming technology was developed to fabricate a duplex stainless steel sheet for the outer surface of liquid propellant combustion chamber. Superplasticity of this alloy was investigated and forming methodology was analyzed and developed. The experimental results show a complex configuration of aerospace component was successfully fabricated by superpalstic forming of a sheet of duplex stainless steel.

Superplastic Sheet Metal Forming with Focus on the Warm Bulge Test and its In-Process Monitoring

Material characterisation is of prime importance in understanding its response to forming loads, which in turn influence the product design. The flow stress in plastic loading defines the evolution of the yield surface and depends on a variety of factors such as strain, strain rate and temperature. The degree of influence of the strain rate increases at higher temperatures. This effect can be well described with superplastic forming, in which the material is loaded very slowly at superplastic temperatures. This paper deals with monitoring of process parameters during superplastic sheet metal forming of magnesium alloys, with special emphasis on in-process measurements for bulge test purposes at elevated temperatures. The strain evolution near the part‟s pole region has been recorded in-process by using the ViALUX photogrammetric strain analysis system AutoGrid. The recorded data provides a lot of information about the forming process such as evolution of strains, strain rate, flow stress and the limit strains, which allows determining all relevant material and process parameters for superplastic forming.

A planar simple shear test and flow behavior in a superplastic Al-Mg alloy

Superplasticity is generally studied by performing tensile and gas-pressure-bulge tests. In formed parts, however, a variety of strain states, including in-plane shear, are encountered. The understanding of the mechanical response in shear is helpful in the study of superplastic metal forming. In this study, a device for a planar simple shear test was designed and used to perform tests on a superplastic Al-Mg alloy sheet at the elevated temperatures of 500 °C (773K) and 550 °C (823K). In such a test, the incremental rotation of the principal strain axes and specimen-end effects during deformation can complicate the determination of true mechanical response. The possible approximations regarding the strain state in the specimen gage have been investigated. The σe-ee curves developed based on a simple-shear assumption show a lower flow stress than that under uniaxial tension, and strain hardening is related to dynamic grain growth. The rate of strain hardening at a fixed \(\dot \varepsilon \)e level is essentially the same for both uniaxial tension and shear, but the difference in the effective stress between uniaxial tension and shear depends upon strain rate and temperature. This study marks the first known attempt to characterize large strain response for superplastic metals under conditions of simple shear.

A Theory for Stretchiness

Superplastic metal alloys can be easily molded into strong, yet complex shapes for airplanes and cars. A new theory attempts to explain at the atomic level why such materials can stretch so easily.

Analysis of limit strains of a high strain-rate superplastic AI6061/20SiCw composite under equibiaxial tension

Since the publication of the pioneering work by Marciniak and Kuczynski, numerous research papers have appeared in the literature for the theoretical prediction of limit strains. However, less work has been done in the analysis of limit strains of high-strain-rate superplastic metal matrix composite sheets. In this paper, limit strains of a A16061/SiCw composite sheet deformed at a temperature of 873 K and under equibiaxial tension were predicted based on the M-K and a plastic damage model. It is shown that the predicted limit strain increases with increasingf o, and decreases with increasingD Bo/DAo, and it is able to predict limit strains of MMC sheets under equibiaxial tension in a reasonable agreement with the experimental results even without assuming any initial geometrical defect.

Microstructural characteristics and deformation properties in superplastic intermetallics

Abstract Superplasticity in intermetallic alloys is reviewed. Intermetallics which have been demonstrated to be superplastic include nickel-based (Ni 3 Al, Ni 3 Si), iron-based (Fe 3 Al, FeAl), and titanium-based (Ti 3 Al, TiAl) alloys. Superplasticity has been recorded in both quasi-single-phase and two-phase intermetallic alloys. The microstructural characteristics and deformation properties of superplastic intermetallics are in many ways similar to those observed in conventional superplastic metal alloys. In the present paper, some of the unusual microstructural features pertinent to superplastic intermetallics are described. Two interesting features are especially highlighted: intermetallics can exhibit superplastic properties in a relatively coarse-grained condition (>100 μm); and intermetallics with a metastable, inhomogeneous microstructure can exhibit superplasticity at low temperatures. Examples are given for both cases. In addition, the superplastic deformation mechanisms as well as microstructural characteristics in different intermetallics are discussed.

超塑性Ｓｉ３Ｎ４／６０６１Ａｌ複合材料の空洞形態に及ぼす強化材形状の影響

Cavitation of superplastic metal matrix (6061Al alloy) composite reinforced by 20% volume fraction of Si3N4, particulate and Si3N4, whisker has been investigated. A constant stress tention test was carried out at temperature of 818K and stress of 8MPa for the composite containing Si3N4, particulate, and at 833K, 10MPa for the composite containing Si3N4, whisker. Volume of cavity in the Si3N4p/6061Al composite was larger than that in the Si3N4w/6061Al composite at a range of strain up to 1.5. Both composites already included the volume of cavity of 0.6-0.8% at a strain of 0.2. Cavity volume fraction exponentially increased with increasing strain. Most cavities of both composites were nucleated at the interface of matrix and reinforcements. Cavities in the Si3N4p/6061Al composite were almost granular and those in the Si3N4w/6061Al composite were either granular or flat.

Processing and Development of Superplastic Metal Matrix Composites

Processing and Development of Superplastic Metal Matrix Composites

A comparative study of cavitation characteristics in composite and 7475 aluminum alloy

Recently, it has been demonstrated that many aluminum matrix composites with discontinuous SiC or Si[sub 3]N[sub 4] show superplastic behavior. In particular, it should be noted that some aluminum matrix composites show superplasticity at high strain rates (> 10[sup [minus]2] s[sup [minus]1]). It is well established that cavitation occurs during superplastic flow in a wide number of metallic materials. However, the cavitation behavior in superplastic metal matrix composites is not well understood. It is important to investigate characteristics of cavitation in metal matrix composites for superplastic forming applications. In this investigation, cavitation in a 20 vol% Si[sub 3]N[sub 4p]/Al-Mg-Si composite, which exhibits superplasticity at high strain rates, has been investigated and the data of the composite have been compared with those of the superplastic 7475 alloy which is a typical superplastic aluminum alloy.

Superplastic deformation mechanism accommodated by the liquid phase in metal matrix composites

Abstract The accommodation processes for superplastic metal matrix composites are required to release the stress concentration near matrix-reinforcement interfaces because of stress concentration caused by interfacial sliding. An optimum superplastic elongation was found at the temperature where local melting of interfaces was confirmed by in situ transmission electron microscopy observation. It is postulated that superplastic flow in metal matrix composites is controlled by a grain-boundary sliding mechanism accommodated with relaxing the stress concentration by an isolated liquid phase at matrix-reinforcement interfaces.

Superplastic sheet metal forming of a generalized cup part ii: nonuniform thinning

Superplastic sheet metal forming of a generalized cup part ii: nonuniform thinning

Superplastic sheet metal forming of a generalized cup part i: uniform thinning

A computational process model for the super plastic formation of a generalized cup is presented that takes into account the variation in thinning in the unsupported region. The relative pole to edge thinning arises due to the change in the state of stress from balanced biaxial at the pole to plane strain at the edge. Using kinematic conditions and material constitutive equations, a relationship between the instantaneous thickness at the pole and edge is developed. An equation for thickness variation from center to edge in terms of convected coordinates is postulated. Process parameters including thickness profile and pressure-time cycle for the generalized cup are determined using an incremental formulation. The solution developed in Part II depends on process and material parameters, unlike the uniform thinning model. The thickness profile for different shapes like the dome, cup, and cone formed from superplastic aluminum 7475 and aluminum-lithium alloys are compared with experimental results.