CORROSION RESISTANCE OF Al-12Si-1Ti ALLOY REINFORCED WITH IN-SITU Mg2Si PARTICULATE

1. 5th International Advanced Technologies Symposium (IATS’09), May 13-15, 2009, Karabuk, Turkey
CORROSION RESISTANCE OF Al-12Si-1Ti ALLOY REINFORCED WITH
IN-SITU Mg2Si PARTICULATE
Ali PALTA1, Aydın DURMAZ, Görkem YARGÜL, Ferdi YILDIRIM, Hayrettin AHLATCIa,Mustafa ACARERb
1
Karabuk University, Technical Education Faculty, Department of Metals, KARABUK/TURKEY
a
hahlatci@karabuk.edu.tr
b
macarer@karabuk.edu.tr
Abstract The samples for microstructural analysis were initially
polished with 80, 400, 600 ,800 and 1000 grit SiC emery
In this study, corrosion behavior of Al-12Si-20Mg and Al– papers and finally were polished with 1 µm diamond paste.
12Si-20Mg-1Ti alloys was investigated. Characterizations The corrosion morphology (subsurface) of the corroded
of the alloys were carried out by microstructural test samples were examined by using optical microscopy.
examinations and corrosion tests. Microstructural results
showed that precipitation of the Mg2Si phases was For immersion testing, samples with the size of 10 mm in
observed in matrix of the investigated alloys as two length and 15 mm in diameter were ground up to 1000 grit
different morphologies; i.e. as a polyhedral primary particle SiC emery papers and polished 1 µm diamond paste. After
and as a chinese script. Upon addition of 1 wt. %Ti, Al3Ti well cleaned with acetone, these samples were weighed
intermetallic precipitated in the alloy. Corrosion tests were and then immersed in 30 g/l NaCl+10 ml/l HCl solution for
carried out by immersing the alloys in “30 g/l NaCl+10 ml/l 24 h. The amount of solution in the baker was estimated
HCl” solution. Evaluation of corrosion was determined by by taking into account the surface area of the specimens
measuring weight loss for 24 hours. Corrosion resistance as 0.3 ml/mm2. After the immersion test, these samples
of the alloy increased with 1 wt %Ti addition. were cleaned with a solution containing HNO3 (ASTM
G110) for 2 min to remove the corrosion products. Finally
Keywords: Aluminum-Magnesium-Silicon, Mg2Si, In- situ they were well cleaned with distilled water and were
composite, Corrosion, Al3Ti Intermetallic. weighed. The corrosion rate was calculated from the initial
and final weights and was expressed as weight loss per
1. Introduction unit area and time (g/cm2xh). At least three samples taken
from each casting were subjected to immersion test and
Hyper-eutectic Al–Si alloys preferentially have received average values are reported.
considerable attention for wear related applications
including combustion engines, pistons, liners [1,2]. 3. Results and Discussion
Elements such as Cu, Si and Ti which formed
intermetallics, were added to the matrix in order to improve Figure 1 shows optical micrographs of the Al-12Si-20Mg
mechanical properties of Al alloys. Since the intermetallic alloy without and with 1 wt. %Ti addition. The
compound of Mg2Si exhibits low density, low thermal homogenized alloy microstructure consist of thin needle
expansion coefficient, high melting temperature, high and thick needle shaped light gray colored, polygonal
hardness and elastic modulus, Mg is an attractive alloying shape dark particles, dark gray colored chinese script and
element for in-situ reinforcing of Al–Si alloys [3-7]. white colored matrix. According to the results of the
When alloy modification is carried out to improve its previous studies [8,14], these constituents were identified
mechanical properties, microstructural changes are as matrix (white colored), Si (thin needle shaped light gray
inevitable and therefore its corrosion behavior. Since colored phase), Al3Ti (thick needle shaped light gray
corrosion behavior of Al alloys is highly susceptible to its colored phases) and Mg2Si (polygonal shape dark particles
microstructure, these intermetallics formed in its matrix and dark gray colored chinese script). It was also noted
firmly play an important role [8-11]. Therefore, the aim of that Mg2Si phase with two different morphology was
thisstudy was to investigate the effect of 1 wt. %Ti addition observed in the microstructure in agreement with the
on corrosion behavior of Al-12Si -20Mg alloy. literature [8, 12, 13].
2. Experimental Work Figure 2 shows the effect of Ti additions on the corrosion
rate of the investigated alloys in 30 g/l NaCl+10 ml/l HCl
The alloys were prepared by melting of Al-12Si which then solution. It was observed from the immersion test results
alloyed with Mg of 20% and Ti of 1 %.Melting was carried that the alloying addition of 1 wt. %Ti improved the
out in a graphite crucible placed in an electrical resistance corrosion resistance. As illustrated in Figure 2, addition of
furnace under a flux cover. Mg was added to the Al–12Si 1 wt. %Ti to the Al-12Si-20Mg alloy reduced the corrosion
2
alloy melt at 1073 K along with 0.05% of Sr, 0.20% of red rate from 0.98 to 0.53 (g/cm xh).
phosphorous and 0.30% of NaCl+30MgCl2+10KCl
mixtures (preheated to 573 K) before charging into the
melt. The melt was then poured at 1173 K into a die mold
which was preheated to 523 K to produce the rod shaped
ingots of 20 mm in diameter and 300 mm in length. After
casting, samples were homogenized at 573 K.
© IATS’09, Karabük Üniversitesi, Karabük, Türkiye

2. Palta , A., Durmaz, A., Yargül , G., Yıldırım, F., Ahalatcı, H. ve Acarer, M.
Alloy Microstructure This clearly indicates that Mg2Si and Al3Ti phases are
Al- highly stable during corrosion process.
12Si-
20Mg Alloy Subsurface
Al-
12Si-
20Mg
Al-
12Si-
20Mg-
1Ti Al-
12Si-
20Mg-
1Ti
Figure 1. Optic Micrographs of the investigated alloys.
1,2 Al-12Si-20Mg Figure 3 Subsurface of the corroded Al-12Si-20Mg and Al-
12Si-20Mg-1Ti alloys.
Al-12Si-20Mg-1Ti Improvement in corrosion behavior of the Al-12Si-20Mg
1 alloy due to 1 wt.%Ti addition may be attributed to
Corrosion Rate (g/cm2*h)*10-3
incorporate into the protective oxide film and thus
increasing its stability [10, 11].
0,8
Conclusion
0,6 The following conclusion can be drawn from the results of
the present investigation conducted on the homogenized
Al-12Si-20Mg alloy without and with 1 wt.%Ti addition.
0,4 1. Both of the Al-12Si-20Mg with and without 1 wt.%Ti
has Mg2Si with two different morphology such as
polygonal shape particles and chinese script.
2. Upon addition of 1 wt. %Ti, Al3Ti intermetallic
0,2 observed in the microstructure.
3. The corrosion resistance increased with addition of 1
wt. %Ti.
0
Acknowledgment
Figure 2. Effect of 1 wt. %Ti content on the corrosion rate
This work was supported by the Research Fund of The
Figure 3 shows the subsurface micrographs of the Scientific and Technical Research Council of Turkey
immersed samples in 30 g/l NaCl+10 ml/l HCl solutions. It (TUBITAK).
was noted that roughness of the corroded sample surface
had been decreased by the addition of 1 wt.%Ti. Corrosion
had occurred by dissolution of the matrix and eutectic
Mg2Si phase. On the other hand most of the polygonal
Mg2Si and blunt needle Al3Ti phases still appear intact.

3. Palta , A., Durmaz, A., Yargül , G., Yıldırım, F., Ahalatcı, H. ve Acarer, M.
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