Abstract: Ultrahigh carbon steel containing 1.6 wt pct C was processed to create microduplex
structure consisting of fine-spheroidized carbides and fine ferrite grains. Elongation-to-failure tests
were conducted at strain rates from 10-4s-1 to 15×10-4s-1, and at temperatures from 600 °C to 850 °C.
The steel exhibited superplasticity at and above 700 °C when testing at a strain rate of 10-4s-1, and at
800 °C when testing at strain rates of 7×10-4s-1 and slower. The grains retained the equiaxed shape
and initial size during deformation; dynamic grain growth was not observed after superplastic
deformation, whereas carbide coarsening was observed. It is concluded that the fine ferrite grains or
austensite grains are stabilized by the grain boundary carbides, and grain-boundary sliding
controlled by grain boundary diffusion is the principal superplastic deformation mechanism at
temperatures in the range of 700-850 °C.
Abstract: Superplastic deformation (SPD) behaviors of two fine-grained materials produced by
ECAE and hot rolling methods have been contrastively studied in this paper. It is found that the
optimum superplastic condition in as-ECAEed material was at 350°C and 1.7×10-3s-1 with elongation
to failure about 800%; while in as-rolled material, the largest elongation to failure about 1000% was
obtained at 480°C and 5.02×10-4s-1. Microstructure observation showed that grain evolution and
cavitation behavior were different in these two materials during superplastic deformation. The
controlled mechanisms for superplasticity, i.e. grain boundary sliding (GBS), dislocation creep and
diffusional creep, at different deformation conditions were discussed in terms of strain rate sensitivity
coefficient, stress exponent and activity energy.
Abstract: Superplastic forming (SPF) of magnesium alloys has received increasing attention in the
recent past. The aim of this presentation is to review recent works dealing with SPF of Mg alloys with
a three-fold objective: i. How to produce fine or ultra fine grained (UFG) microstructures? ii. Are
there specifities in superplastic deformation mechanisms? iii. How SPF Mg alloys resist to
cavitation? Deformation mechanisms as well as damage variations in the superplastic regime will be
preferentially discussed in relation with grain size, content in intermetallic particles and diffusion
kinetics. For the sake of illustration, some results concerning the superplastic behaviour of UFG
magnesium alloys produced by severe plastic deformation will be presented since such
microstructures exhibit particularly attractive superplastic properties at quite low temperatures.
Abstract: Accurate constitutive modeling of superplastic deformation is critical for successful
simulation and optimization of superplastic forming. The selection of the forming pressure profiles in
gas blow forming of superplastic materials is still based on trial and error due to the limited predictive
capabilities of current models describing superplastic deformation. In general, these models are based
on uniaxial loading condition, assuming isotropic behavior. In this work, we examine the biaxial
bulge forming of AZ31 magnesium alloy using pressure profiles derived from different available
analytical models. The results clearly show the need for more accurate description of superplastic
deformation to improve predictive capabilities. In addition, a pressure profile that is generated using
FE in conjunction with a microstructure-based constitutive model is used and the results indicate
better ability to predict the height of the bulged sheet.
Abstract: Magnesium alloys show promise in meeting the demand for materials of lighter weight and
higher rigidity. Mg alloys are hard to process and normally require grain refining for improved
formability and mechanical properties. To process these fine-grained Mg alloys effectively, it is
important to relate their load stress and mechanical properties to changes in their microstructures.
Using a biaxial tensile machine and cruciform specimens, to evaluate the mechanical properties,
microstructure, and plasticity, in a high temperature biaxial stress state, used of AZ31 Mg alloy sheet.
With biaxial deformation, grain boundary slide occurred more frequently than with uniaxial
deformation, causing grain boundary separation and formation of micro-voids between the grains. In
the vicinity of the cracks and at the locations of grain boundary separation, although deformation
temperature at higher than the recrystallization temperature, fine grains (about 2 )m) showing in
duplex grain structures were formed locally. The formation of duplex grain structures as a result of
local formation of fine grains during the deformation process is a major issue to be solved from the
viewpoint of plasticity processing.
Abstract: The superplasticity of a hot-rolled AZ31 Mg alloy was investigated by uniaxial tensile tests
at temperature range 250-450oC and strain rate range 0.7×10-3-1.4×10-1s-1. Superplastic formability of
the alloy was evaluated by gas bulging test at elevated temperatures. The threshold stress for grain
boundary sliding (GBS) was calculated and the topography during superplastic deformation was
observed by SEM. It is found that, at 400 oC and 0.7×10-3 s-1, the maximum elongation reaches
362.5%. GBS is the predominant deformation mechanism and characterized by a pronounced
improvement in homogeneity with increasing temperatures, indicating a transformation of GBS mode
from cooperative GBS (CGBS) to individual GBS (IGBS). The improved homogeneity of GBS can
be interpreted in terms of decreased threshold stress with increasing temperatures. Gas bulging test
demonstrates that the temperature for the best superplastic formability is 400 oC and a hemispherical
part with a specific limiting dome height of 0.51 was obtained, suggesting good application prospect
for this alloy.
Abstract: The superplasticity of magnesium alloy is important in industrial application. However
the superplastic deformation of casting magnesium alloy is hard to be realized. In this paper, the
stress–strain behaviors of casting AZ31 magnesium alloy with various strain rates at different
deformation temperatures were investigated. The alloy was tested in the tensile condition with
initial grain size of 25μm. It was found that the elongation of the alloy at 400°C with ε&
s-1 is almost 200%. According to the results of uniaxial tensile experiment, the alloy exhibited
superplastic deformation behavior with the slow stain rate in a temperature range of 350 to 450°C.
The microstructures deformed and undeformed samples were observed with aid of optical
Abstract: A new SPF/DB technology using gasification agent as pressurization mediator was
proposed in this paper. The forming principle of SPF/DB using the agent was represented. Dies used
for the forming process was designed and manufactured, and new gasification agent N11 which is
white solid powder at normal temperature and it is easy to encapsulate and keep was developed for
magnesium alloy. ZK60 magnesium alloy with a thickness of 1mm and grain size of 7.9μm was
selected to conduct the experiment of SPF/DB. Corrugated ZK60 magnesium alloy parts were well
formed under the temperature between 653K and 673K and forming time of 50 minutes. SEM was
used to observe the microstructures of the diffusion bonding joints. The result shows that the joints
were well bonded.
Abstract: The superplasticity of LY12 alloy was reviewed in this paper. Complex component was
extruded by taking advantage of the superplasticity of supplied LY12 alloy. The research
demonstrates that in isothermal compression process dynamic recrystallization may occur in
supplied LY12 alloy. In superplastic forming test grain refinement was combined with initial
extrusion step utilizing dynamic recrystallization to complete grain refinement, which ensured the
superplasticity in supplied LY12. In the early stage of extrusion, using high deformation speed and
large amount of deformation can result in grain refinement, which primarily satisfied the demand of
the superplasticity. In the final stage, the forming speed decreased sharply so that the optimum
strain rate was satisfied and the complicated component can be extruded successfully. The resulted
product has reasonable flowing traces, which improves its service performance.
Abstract: In this paper, an ultra-fine grained AZ31 magnesium alloy sheet with grain size less than
3μm was generated by three-run accumulative roll bonding of as cast alloy at a deformation
temperature of 350°C and a reduction of 80% for each pass. The microstructures on the different ARB
stages were observed and superplasticity examination in the ultrafine grained AZ31 alloy were carried
out at a fixed temperature of 300°C and varied strain rate ranging from 10-4 to 10-1 s-1. It is indicated
that significant grain refinement was mainly achieved in the first run and gradual uniformity of grain
size in the next by continuous dynamic recrystalization. Besides, a superplastic deformation with a
moderate elongation-to-fracture of 316% was obtained at a strain rate of 10-2 s-1 indicating a low
temperature and high strain rate superplasticity, while a maximum elongation-to-fracture of 562%
at10-4 s-1. The strain rate sensitivity exponent as high as of 0.34-0.41 implies the dominant role of
grain boundary sliding in superplastic deformation at strain rate ranging from 10-3 to 10-2 s-1. The
results indicate a possible approach to produce magnesium alloy sheet with fine grain and excellent
deep drawing workability.