Influence of T6 and T73 tempers on
hardness and corrosion resistance of
hot-extruded Al7075-SiCp composites
Journal Name:
- Dicle Üniversitesi Mühendislik Fakültesi Mühendislik Dergisi
Keywords (Original Language):
Author Name | University of Author | Faculty of Author |
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Abstract (2. Language):
In this study, the influence of T6 and T73 tempers on
the microstructure, hardness and corrosion
resistance of Al7075 matrix composites reinforced
with SiC particle fabricated by extrusion of powder
metal compacts were investigated. For this purpose,
powder mixtures obtained by addition of average 32
μm sized SiC particles with various ratio (5, 10, 15
and 20 wt%) to AA7075 aluminum alloy powders
(wt.% composition: 4.78% Zn, 1.84% Mg, 1.45%
Cu, 0.24% Si, 0.25% Cr, 0.26% Mn, 0.23% Fe and
Al bal.) were cold pressed under uniaxial pressure
(350 MPa). The pressed compacts were heated at
480 °C for 1 hour and then extruded into 12 mm
diameter bars. After extrusion, all the samples were
solution treated at 480 °C with a soaking duration of
60 min and then water quenched. For T6 temper, the
solution treated samples were aged at 120 °C for 24
h. For T73 temper, the solution treated samples
were aged at 110 °C for 8 h and then at 175 °C for 8
h in two stages.
Characterization of the produced alloy and
composite samples included metallographic
examination, hardness measurement and density
determination. Chemical composition of the AA7075
alloy was analyzed by XRF. The phases and
morphology of samples were examined by XRD
(Rigaku-Ultima IV) and SEM/EDX (Carl Zeiss Ultra
Plus Gemini Fesem). The relative densities of the
extruded AA7075 alloy and AA7075/SiC composites
were measured by Archimedes’ principle. The
hardness values of the samples were measured on
the polished sections of the samples by Brinell
indentation (QNESS Q250M) using a ball with
diameter of 2.5 mm under a load of 31.25 kg.
For preparation of samples for exfoliation corrosion
tests, the sample surfaces were ground with silicon
carbide papers and then polished 6 μm alumina
paste. To determine of the corrosion resistance, the
alloy and composite samples were exposed to EXCO
corrosion solution for 4, 8 and 16 hours. The
corrosion tests were immersion tests where the
weight loss method was used. The samples were first
weighed before being immersed in EXCO corrosion
solution and later taken out after 4, 8 and 16 h
respectively.
SiC particle addition caused a significant increase
in the density of the composite samples, and the
theoretical density was much closer to the 10%
particulate additive composites. In addition, further
increase in the amount of SiC particle cause the
formations of clustering and finally initiates the
formation of pores and weak regions in the
composite.
SiC particle addition caused a significant increase
in the hardness of alloy and composite samples
compared with that alloy. The results reveal that the
highest hardness values were achieved with T6 heat
treated samples while the hardness increases as the
weight fraction of the reinforcement increases.
Corrosion tests shows that the highest corrosion
resistance in both heat treatment types with 10% SiC
particle reinforced specimens. T73 temper improved
the corrosion resistance of samples, while decreased
the hardness about 15%-20% compared to T6
temper.
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Abstract (Original Language):
Bu çalışmada, toz metal kompaktların sıcak ekstrüzyonu ile üretilen SiC partikül takviyeli AA7075
Al matrisli kompozitlerin mikroyapı, sertlik ve korozyon dayanımına T6 ve T73 ısıl işlemlerinin
etkisi incelendi. Bu amaçla; AA7075 alüminyum alaşım tozlarına ağırlıkça farklı oranlarda (% 5,
10, 15 ve 20) ortalama 32μm boyutlu SiC partikül ilave edilerek elde edilen toz karışımları, tek
yönlü basınç (350 MPa) altında soğuk olarak preslendi. Preslenmiş kompaktlar 480 °C’de 1 saat
bekletildikten sonra 12 mm çaplı çubuklar halinde ekstrüze edildi. Ekstruzyon işleminden sonra
numunelere T6 ve T73 ısıl işlemleri uygulandı. Alaşım ve kompozit numunelerin yoğunluk, sertlik,
mikroyapı, kimyasal kompozisyon ve faz yapıları uygulanan çeşitli test ve analizlerle belirlendi.
Korozyon dayanımları 4, 8 ve 16 saat olmak üzere farklı sürelerde EXCO korozyon çözeltisine
maruz bırakılan numunelerin ağırlık değişimleri ile belirlendi. Yapılan ölçümler, takviye elemanı
miktarındaki artışa bağlı olarak sertlik değerlerinin de arttığını ve en yüksek sertlik değerlerine T6
ısıl işlemli numunelerde ulaşıldığını gösterdi. Yapılan korozyon testleri, matris yapıya ilave edilen
SiC partiküllerinin ve uygulanan T73 ısıl işleminin kompozit numunelerin korozyon direncinde
kayda değer bir artış meydana getirdiğini ve en yüksek korozyon direncinin %10 SiC partikül
takviyeli kompozit numunelerde elde edildiğini gösterdi. T6 ısıl işlemi ile karşılaştırıldığında T73
ısıl işlemi, alaşım ve kompozit numunelerin korozyon direncinde artış meydana getirirken, sertlik
değerlerinde %15-20 oranında azalmaya neden olduğu tespit edilmiştir.
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