Superplastic Capability Research Articles

Research on Superplastic Zn-22Al Alloy with a Large Size to a New Seismic Damper

To develop a superplastic damping device, the mechanical properties and superplastic capability of Zn-22Al alloy with a large size in the rolled samples were investigated. It is indicated that the alloy with a large size has some advantage properties, such as high ductility, low yield stress and low work hardening at room temperature, which is very useful to a seismic damper.

The Development of Superplastic Magnesium Alloy Sheet

While magnesium alloys are routinely used in engineering applications in the form of net shape castings, applications for sheet product have been limited due to the poor cold formability of magnesium combined with the perceived expense of sheet. The issues associated with poor cold formability could largely be overcome if magnesium alloys were to be superplastically formed. Superplasticity in magnesium is well established with research papers on the subject dating back to the late 1960s. In recent years, interest in this area has grown to the point where a number of companies have successfully superplastically formed prototype automotive panels from magnesium alloy sheet. Concurrent to this the scientific community have demonstrated superplasticity in a wide range of magnesium alloys using processing techniques ranging from the exotic (severe plastic deformation) to the mundane (traditional warm rolling). Work by the current authors has shown, rather surprisingly, that superplasticity can be achieved in magnesium alloys in the as-cast condition. This has led to some initial exploratory work involving twin roll casting. The concept being that affordable superplastic magnesium sheet could be produced via twin roll casting with only limited rolling reduction to final gauge. This paper describes the superplastic behaviour (in uniaxial tension) and microstructure of sheet processed from strip cast AZ31 and AZ91. The experimental material has included strip cast AZ91 subjected to large shear strains immediately prior to casting. The material was tested in the as-cast condition and after warm rolling to a number of gauges. Industrially useful superplastic capability was demonstrated in the strip cast alloys. Furthermore, good superplastic capability was also demonstrated in sheet subsequently rolled from the cast metal and rolling strain did not significantly influence the ductilities obtained. The mechanism for achieving superplasticity in as-cast magnesium alloys will be considered and the contrasting deformation characteristics of AZ31 and AZ91 will be discussed in terms of m value analysis and microstructural characterisation.

The Development of Superplastic Magnesium Alloy Sheet

While magnesium alloys are routinely used in engineering applications in the form of net shape castings, applications for sheet product have been limited due to the poor cold formability of magnesium combined with the perceived expense of sheet. The issues associated with poor cold formability could largely be overcome if magnesium alloys were to be superplastically formed. Superplasticity in magnesium is well established with research papers on the subject dating back to the late 1960s. In recent years, interest in this area has grown to the point where a number of companies have successfully superplastically formed prototype automotive panels from magnesium alloy sheet. Concurrent to this the scientific community have demonstrated superplasticity in a wide range of magnesium alloys using processing techniques ranging from the exotic (severe plastic deformation) to the mundane (traditional warm rolling). Work by the current authors has shown, rather surprisingly, that superplasticity can be achieved in magnesium alloys in the as-cast condition. This has led to some initial exploratory work involving twin roll casting. The concept being that affordable superplastic magnesium sheet could be produced via twin roll casting with only limited rolling reduction to final gauge. This paper describes the superplastic behaviour (in uniaxial tension) and microstructure of sheet processed from strip cast AZ31 and AZ91. The experimental material has included strip cast AZ91 subjected to large shear strains immediately prior to casting. The material was tested in the as-cast condition and after warm rolling to a number of gauges. Industrially useful superplastic capability was demonstrated in the strip cast alloys. Furthermore, good superplastic capability was also demonstrated in sheet subsequently rolled from the cast metal and rolling strain did not significantly influence the ductilities obtained. The mechanism for achieving superplasticity in as-cast magnesium alloys will be considered and the contrasting deformation characteristics of AZ31 and AZ91 will be discussed in terms of m value analysis and microstructural characterisation.

Factors influencing superplastic behavior in a magnesium ZK60 alloy processed by equal-channel angular pressing

Processing by equal-channel angular pressing was used to refine the grain size of a magnesium ZK60 alloy to ∼0.8 μm and introduce a superplastic capability. Superplastic elongations up to >1000% were achieved at temperatures of 450 and 473 K but the superplastic behavior was lost at 493 K because of grain growth. The strain rate sensitivity under optimum superplastic conditions was measured as ∼0.5 which is consistent with conventional superplastic flow.

The manufacture of superplastic Magnesium alloy sheet

AbstractProbably because of their propensity to dynamically recrystallise, superplastic behaviour can be obtained from magnesium alloys considerably more easily than from comparable aluminium alloys. In some cases even as cast magnesium alloys can exhibit reasonable superplasticity and there appears no need for the special alloying additions or complex thermal mechanical treatments required by aluminium alloys such as AA2004 or AA7475. The paper describes the superplastic behaviour (in uniaxial tension) and microstructure of sheet processed from strip cast AZ31 and AZ91. The material was tested in the as‐cast condition and after warm rolling to a number of gauges. Industrially useful superplastic capability was demonstrated in strip cast AZ31 and AZ91 in the as cast condition. Furthermore good superplastic capability was also demonstrated in sheet rolled from the cast metal and the ductilities obtained were not significantly influenced by rolling strain. Twin roll strip casting represents a feasible and simple route for the production of superplastic material either for use in the as cast condition or after rolling to the required gauge.

Grain Refinement of an Al-Cu-Mg Alloy by Microalloying and Common Thermo-Mechanical Treatment

Heavy deformation plus micro alloying could be an effective way to obtain ultrafine grain structure of metals. In the present work, an Al-Cu-Mg alloy was microalloyed with Zr to obtain homogeneous precipitates and then heavily deformed by conventional forging at high temperature. The possible refining processing routes were studied and the superplasticity behaviors of the alloy was investigated. Results show that the micro alloyed alloy can be stably refined to 3-5μm under conventional processing routes. The Al-3Zr precipitates act both as additional sites to enhance recrystallization nucleation rate and pins to impede grain growth to increase the thermal stability of the fine grain structure. However, as the Al3Zr precipitates remains along grain boundaries, the superplastic capability of the material is not high. At 430°C with 1×10-4S-1 strain rate, the elongation obtained was 260%.

An Experimental Study on Superplastic Behaviors of Magnesium Alloy Sheet

An experimental study on superplastic forming behaviors and microstructure characters of commercial magnesium alloy sheet AZ31B is presented in this paper. The main experimental results show that the commercial magnesium alloy AZ31B sheet has superplastic capability. For the received sheet without any pre-processing, the maximum elongation is 295%. The dynamic recrystallization and grain refinement can be found, In the case of temperature <350°C, and the grain growth appears if temperature ≥ 350°C. The superplastic behaviors can be improved by controlling the dynamic recrystallization and grain refinement. Some experimental results of free superplastic bulging are presented in this paper. The results show that influence of temperature on forming capability is much less than the influences of temperature on elongation. In addition, the maximum principle strain

Alloy design of gamma titanium aluminides based on phase diagrams

Abstract Phase stability in the TiAlX (X = Cr, Mo and W) system has been investigated at 1473 and 1573 K by the following methods: microstructure observation of quenched specimens, diffusion coupling experiments, thermal analysis of DTA and in situ observation of X-ray diffraction. The ternary phase diagrams of TiAlX system are proposed; additions of Cr, Mo and W stabilize the β phase in the ternary phase diagrams. The tendency of ‘β stabilizer’ is in the following order: 6 at% Cr = 3 at% Mo = 1 at% W ≒ 10 vol% β phase. In these Ti-Al-X ternary systems, the α + β + γ three-phase coexisting region is close to the TiAl binary line and sifts slightly toward a higher concentration of Al as temperature increases. Based on the ternary phase diagrams, (γ + β) TiAl having a super-plastic capability and partial lamellar (P-L) microstructure which shows relatively well balanced mechanical properties from room temperature to elevated temperatures have been rationalized.

High-strain-rate superplasticity of an AL2009-SICw composite

Discontinuously reinforced aluminium composites are considered to be excellent candidates for aerospace and automobile industries. However, their formability and machinability needs to be understood first before they can be widely used in these industries. Therefore, a lot of research effort has been spent in the study of the superplasticity of such composites over the past decade. The superplastic capability of many discontinuously reinforced aluminium matrix composites [1–7] has been discovered. Al 2009=SiCw composite is attractive for its high strength, stiffness and thermal stability and an ideal substitute for titanium used at service temperatures betwen 366 and 450 K. Also this material can be used in the sporting goods industry. Up to the present day, the superplastic deformation of Al 2009–20 vol % SiCw composite has not been investigated. In the present study, the superplastic behaviour of a SiC whisker reinforced 2009 aluminium matrix composite has been investigated. A 20 vol % SiC whisker-reinforced 2009 aluminium alloy composite sheet supplied by Advanced Composite Materials Corporation was investigated in this paper. The sheet thickness was 2.286 mm and the size of the â-SiC reinforcement is 0.45–0.65 μm in diameter and 5–80 μm in length. The composite was fabricated by powder metallurgy followed by extrusion and rolling. A typical scanning electron micrograph of the composite is shown in Fig. 1. The distribution of whiskers was found to be uniform and approximately aligned in the direction of the rolling direction. The solidus temperature of the composite was determined by a Du Pont 9900 differential scanning calorimeter (DSC). The solidus temperature of the composite was found to be 812 K when the DSC test started at room temperature and ended at about 893 K with a constant heating rate of 10 K miny1. Superplastic tensile samples with a gauge length of 5 mm and a width of 4 mm were machined from the sheet in the rolling direction. Superplastic tests at temperatures ranging from 723 to 813 K were conducted in an Instron test machine with a ceramic heater furnace. Prior to testing, the specimen was held in the furnace at the specified test temperature for about 20 min to establish thermal equilibrium and all testing was carried out in air at different constant crosshead velocities. The material showed the superplastic ability under certain conditions. The relationship between the total elongation-to-failure and the initial strain rate of the composite at different test temperatures is shown in Fig. 2. A maximum elongation of 190% was obtained at a strain rate of 6:7 3 10y1 sy1 and at 773 K which is far below the solidus temperature, 812 K. A similar phenomenon was also observed for Al2009–15 vol % SiCw composite [8]. That the optimum superplastic temperature was far below the solidus temperature was anomalous because the optimum temperatures of several other superplastic aluminium composites were found to be slightly higher than their solidus temperatures [1–7]. The optimum superplastic strain rate of the superplastic composites was obviously higher than the conventional superplastic strain rate of 10y5 –10y3 s [9] and this was considered to be highly beneficial in the superplastic forming of aluminium composites. The optimum superplastic temperature of several super-

Low temperature superplasticity in 8090 AlLi alloys

There have been a number of aluminum alloys which, after being subjected to appropriate thermomechanical treatments (TMTs), exhibit high strain-rate sensitive superplasticity while deformed at a temperature near 0.9T[sub m]. The current study was intended to develop a series of TMT process which will allow the 8090 Al-Li base alloy to have superplastic capability at temperatures below 450 C so as to suppress to a certain degree of the extensive grain growth and Li-loss; at temperature above 300 C so that the flow stress will not be too high to induce intensive cavitation; and in excess of 400% elongation, thus reaching the level for certain commercial applications, if possible.