3 results listed
In this study, isothermal annealing was performed to
C70 quality steel sheet in a salt bath at 250 °C and 350 °C for 10 s,
1 min, 10 min, and 60 min after austenitizing performed at 850 °C
for 150 s and the samples were then tempered at 415 °C for 150 s.
Effect of these heat treatments on microstructure, hardness and
bending properties was then investigated. Results showed that the
initial ferrite and pearlite microstructure generally transformed
into martensite. Tempered martensitic microstructure was
obtained after tempering heat treatment. Hardness of the samples
has a decreasing tendency with increasing annealing times at a
given annealing temperature. Tempering heat treatment
decreases the hardness values obtained after isothermal
annealing, as expected. However, hardness values after tempering
did not exhibit a significant variation with respect to isothermal
annealing time. As compared to original sample, the application
of tempering after isothermal annealing increases bending
strength, and bending strain also increases getting closer to values
exhibited by the original sample.
International Iron & Steel Symposium
UDCS
Serdar Kuzkaya
Yakup Yurekturk
Faiz Muhaffel
Murat Baydogan
The use of aluminum alloys in automotive industry has greatly increased in recent years. This has been attributed
not only to the issues of fuel economy, but also to those of safety, resource conservation and environmental concerns [1].
High-strength age-hardened 7xxx series Al−Zn−Mg−Cu alloys are widely used for aircraft structures, where they are
subjected to demanding operating conditions [2]. In this study, retrogression and reaging (RRA) heat treatment was
applied to commercial 7075-T6 aluminum alloy (Al–Zn–Mg–Cu), whose chemical composition is shown in Table 1
RRA heat treatment is capable of producing a material with high strength and high corrosion resistance than presented by
the T6 temper. In the retrogression treatment, salt bath furnace was used for heating the samples to 250°C and 280°C for
1 min. After that, the samples taking out of furnace and quenched in cold water of 5-8°C temperature. Subsequently
intermediate deformations were applied to the samples in 2%, 4% and 6% and one sample was left undeformed for
comparison. Following intermediate deformations, the samples were reaged at 120°C for 24 and then cooled to room
temperature in air. In order to investigate effect of intermediate deformation on the strength and strain hardening exponent
as the indicators of formability characteristics of RRA’ed 7075 alloys, tensile tests were carried out to determine yield
strength, ultimate tensile strength and tensile strain hardening exponent (n-value). Hardness and electrical conductivity
measurements were also performed on the samples. Variation of strength and elongation at fracture of the samples
retrogressed at 250°C (a) and 280°C (b) and then reaged as a function of intermediate deformation is shown in Figure 1
It is obviously seen that strength values decrease whereas ductility (elongation at fracture) generally increases with
increasing retrogression temperature. On the other hand, intermediate deformation has not any significant effect on
strength and ductility for both retrogression temperatures. Figure 2 shows variation of strain hardening exponent of the
samples retrogressed at 250°C and 280°C and then reaged as a function of intermediate deformation. It is very apparent
that retrogression temperature has a strong effect on strain hardening exponent, whose value increases with increasing
retrogression temperature. Figure 3 indicates variation of hardness and electrical conductivity of the samples retrogressed
at 250°C and 280°C and then reaged as a function of intermediate deformation. It is obvious that hardness decreases
whereas electrical conductivity increases with increasing retrogression temperature. It is well known that electrical
conductivity is a good indicator of corrosion resistance of the samples [3]. Therefore, this can be said that corrosion
resistance increases with increasing retrogression temperature, as expected. Overall results demonstrated that higher
retrogression temperature is beneficial in the point of formability because it increases ultimate tensile strength to yield
strength ratio and strain hardening exponent as well. In the view point of intermediate deformation, it was shown that it
does not significantly effect of strength, hardness and electrical conductivity of the samples after RRA, but lead to some
decrement in strain hardening exponent, which adversely affects the formability characteristics of 7075 RRA alloy.
International Symposium on Light Alloys and Composite Materials
UHAKS
Armin Rashidi
Yakup Yurekturk
Murat Baydogan
Titanium based materials have wide range of applications at elevated temperatures including highly oxidizing
and corrosive service conditions. Even though natural oxide film of titanium is very stable at room temperature and
resistant to corrosion and oxidation, it is very brittle at temperatures higher than 650°C. Therefore, a protective layer at
the surface would provide increased lifetime and performance for titanium based materials [1, 2]. For this purpose various
methods including Al films sputtering, magnetron sputtering, pack cementation, pack aluminizing have been researched
so far. Amongst these methods, hot dip aluminizing is a promising method for coating titanium materials as it is a simple,
quick and inexpensive alternative with respect to the other methods [3,4].
International Symposium on Light Alloys and Composite Materials
UHAKS
Mert Altay
Yakup Yurekturk
Murat Baydogan