Abstract: Microstructure and mechanical properties of AZ91D
Mg alloys for nonflammable use, containing Ca and Y, were
investigated in this study. Solid solution treatment of AZ91D Mg alloy
with Ca and Y was successfully conducted at 420oC and
supersaturated microstructure with almost all beta phases resolved into
matrix was obtained. After solid solution treatment, the alloy was
annealed at temperatures of 180 and 200oC for time intervals from 1
min to 48 hrs and hardness of each condition was measured by
micro-Vickers method. Peak aging conditions were deduced from the
results as at the temperature of 200oC for 10 hrs. Hot rolling was also
carried out at 400oC by the reduction ratio of 0.6 through 5 passes
followed by recrystallization treatment. Tensile and compressive
properties were measured at room temperature on the specimens of
each process, i.e. as-cast, solution treatment, hot rolling, and
recrystallization.
Abstract: Heat treatable aluminum alloys such as 7075 and
7055, because of high strength and low density, are used widely in
aircraft industry. For best mechanical properties, T6 heat treatment
has recommended for this regards, but this temper treatment is
sensitive to corrosion induced and Stress Corrosion Cracking (SCC)
damage. For improving this property, the over-aging treatment (T7)
applies to this alloy, but it decreases the mechanical properties up to
30 percent. Hence, to increase the mechanical properties, without any
remarkable decrease in SCC resistant, Retrogression and Re-Aging
(RRA) heat treatment is used. This treatment performs in a relatively
short time. In this paper, the RRA heat treatment was applied to 7055
aluminum alloy and then effect of RRA time on the mechanical
properties of 7055 has been investigated. The results show that the
40-minute time is suitable time for retrogression of 7055 aluminum
alloy and ultimate strength increases up to 625MPa.
Abstract: Effect of alloying on the microstructure and mechanical properties of heat-resisting duplex stainless steel (DSS) for Mg production was investigated in this study. 25Cr-8Ni based DSS’s were cast into rectangular ingots of which the dimension was 350×350×100 mm3 . Nitrogen and Yttrium were added in the range within 0.3 in weight percent. Phase equilibrium was calculated using the FactSage®, thermodynamic software. Hot exposure, high temperature tensile and compression tests were conducted on the ingots at 1230oC, which is operation temperature employed for Mg production by Silico-thermic reduction. The steel with N and Y showed much higher strength than 310S alloy in both tensile and compression tests. By thermal exposition at 1230oC for 200 hrs, hardness of DSS containing N and Y was found to increase. Hot workability of the heat-resisting DSS was evaluated by employing hot rolling at 1230 oC. Hot shortness was observed in the ingot with N and found to disappear after addition of Y.
Abstract: To evaluate the vigor of wheat seeds and stress of
premature aging effects on germination percentage, root length and
shoot length of five wheat cultivars that include Vynak, Karkheh,
Chamran, Star and Kavir which underwent a period of zero, two,
three, four days in terms of premature aging with 41°C temperature
and 100% relative humidity. Seed germination percentage, root
length and shoot length in these conditions were measured. This
experiment was conducted as a factorial completely randomized
design with four replications in laboratory conditions. The results
showed that each of aging treatments used in this experiment can be
used to detect differences in vigor of wheat varieties. Wheat cultivars
illustrated significant differences in germination percentage, root
length and shoot length in terms of premature aging. The wheat
cultivars; Astar and Vynak had maximum germination percentage
and Karkheh, respectively Kavir and Chamran had lowest percentage
of seed germination. Reactions of root and shoot length of wheat
cultivars was also different. The results showed that the seeds with a
stronger vigor affected less in premature aging condition and the
difference between the percentage of seed germination under normal
conditions and stress was significant and the seeds with the weaker
vigor were more sensitive to the premature aging stress and the
premature aging had more severe negative impact on seed vigor.
Abstract: The present study was undertaken to investigate the
effect of aging parameters (time and temperature) on the mechanical
properties of Be-and/or Zr- treated Al-Mg-Zn (7075) alloys. Ultimate
tensile strength, 0.5% offset yield strength and % elongation
measurements were carried out on specimens prepared from cast and
heat treated 7075 alloys containing Be and/or Zr. Different aging
treatment were carried out for the as solution treated (SHT)
specimens (after quenching in warm water). The specimens were
aged at different conditions; Natural and artificial aging was carried
out at room temperature, 120C, 150C, 180C and 220C for different
periods of time. Duplex aging was performed for SHT conditions
(pre-aged at different time and temperature followed by high
temperature aging). Ultimate tensile strength, yield strength and %
elongation data results as a function of different aging parameters are
analysed. A statistical design of experiments (DOE) approach using
fractional factorial design is applied to acquire an understanding of
the effects of these variables and their interactions on the mechanical
properties of Be- and/or Zr- treated 7075 alloys. Mathematical
models are developed to relate the alloy mechanical properties with
the different aging parameters.
Abstract: The present study was undertaken to investigate the
effect of pre-aging and aging parameters (time and temperature) on
the mechanical properties of Al-Mg-Zn (7075) alloys. Ultimate
tensile strength, 0.5% offset yield strength and % elongation
measurements were carried out on specimens prepared from cast and
heat treated 7075 alloys. Aging treatments were carried out for the as
solution treated (SHT) specimens (after quenching in warm water).
The specimens were aged at different conditions; Natural aging was
carried out at room temperature for different periods of time. Double
aging was performed for SHT conditions (pre-aged at different time
and temperature followed by high temperature aging). Ultimate
tensile strength, yield strength and % elongation as a function of
different pre-aging and aging parameters are analyzed to acquire an
understanding of the effects of these variables and their interactions
on the mechanical properties of Be-treated 7075 alloys.
Abstract: High temperature deformation behavior of cast
Fe-20Cr-5Al alloy has been investigated in this study by performing
tensile and compression tests at temperatures from 1100 to 1200oC.
Rectangular ingots of which the dimensions were 300×300×100 in
millimeter were cast using vacuum induction melting. Phase
equilibrium was calculated using the FactSage®, thermodynamic
software and database. Tensile strength of cast Fe-20Cr-5Al alloy was
4 MPa at 1200oC. With temperature decreased, tensile strength
increased rapidly and reached up to 13 MPa at 1100oC. Elongation
also increased from 18 to 80% with temperature decreased from
1200oC to 1100oC. Microstructure observation revealed that M23C6
carbide was precipitated along the grain boundary and within the
matrix.
Abstract: Effect of aging treatment on microstructural aspects of interfacial layers of the Cu/Al clad sheet produced by differential speed rolling (DSR) process were studied by electron back scattered diffraction (EBSD). Clad sheet of Al/Cu has been fabricated by using DSR, which caused severe shear deformation between Al and Cu plate to easily bond to each other. Rolling was carried out at 100oC with speed ratio of 2, in which the total thickness reduction was 45%. Interface layers of clad sheet were analyzed by EBSD after subsequent annealing at 400oC for 30 to 120min. With increasing annealing time, thickness of interface layer and fraction of high angle grain boundary were increased and average grain size was decreased.