Journal of Alloys and Compounds
Combined effect of high-intensity ultrasonic treatment and Ca addition
on modification of primary Mg Si and wear resistance in hypereutectic
2
Mg–Si alloys
M.E. Moussa a, , M.A. Waly , A.M. El-Sheikh
⇑
a
b
a
Department of Manufacturing Technology, Laboratory of Foundry, Central Metallurgical Research and Development Institute (CMRDI), P.O. 87, Halwan, Egypt
Department of Mining, Petroleum and Metallurgical Engineering, Faculty of Engineering, Cairo University, P.O. 12613, Giza, Egypt
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 May 2014
Received in revised form 8 June 2014
Accepted 20 June 2014
Available online 7 July 2014
The combined effect of high-intensity ultrasonic treatment (HIUST) and 0.3 wt.%Ca addition on modifica-
tion of primary Mg
The results show that without treatment, the dendrites of primary Mg
size. With HIUST or 0.3 wt.%Ca addition, nearly fine uniform and polyhedral shape of primary Mg
achieved. Interestingly, modification and refinement of primary Mg Si arise from the combined effect of
2
Si and wear resistance in the hypereutectic Mg–5 wt.%Si alloy has been investigated.
Si are coarse and non-uniform in
Si are
2
2
2
HIUST and 0.3 wt.%Ca addition. The sample due to combined effect of HIUST and 0.3 wt.%Ca addition has
the best wear resistance due to the lowest weight loss among all the other samples for various loads (10,
Keywords:
Metals and alloys
Microstructure
Metallography
Ultrasonics
30 and 50 N) at constant sliding speed (0.3 m/s). Modification mechanisms resulting in the development
of microstructures are also investigated.
Ó 2014 Elsevier B.V. All rights reserved.
1
. Introduction
this work are to investigate the effect of HIUST on modification of
primary Mg Si in Mg–5 wt.%Si hypereutectic alloy in combination
2
Magnesium alloys are widely applied in the fields which are
with addition of 0.3 wt.%Ca, to explore the modification mecha-
nisms and to investigate the wear resistant of resultant samples.
strongly driven towards weight-reduction, such as automotive,
aeronautic and astronautic industries [1]. Meanwhile, improving
the elevated temperature properties has become a critical issue
for possible application of magnesium alloys in hot components
2. Experimental procedures
2
.1. Materials and processing
[
2]. In recent years, the fascinating properties and promising appli-
cation of hypereutectic Mg–Si alloys have attracted particular
interest due to the formation of thermally stable Mg Si [2,3]. How-
The hypereutectic Mg–5 wt.%Si alloy was melted in a mild steel crucible in an
2
electric resistance furnace under protective gases mixture of tetrafluoroethane
CF CH F, HFC-134a, 1 vol.%) and carbon dioxide (CO , Bal.). Nominal amount of
.3 wt.%Ca in the form of high purity Ca (99.999 wt.%) was added into the melted
(
3
2
2
ever, the hypereutectic Mg–Si alloys prepared by ordinary ingot
metallurgy process showed a very low ductility and strength, due
0
alloy at about 800 °C. The melt was manually stirred for 3 min and then was held
for additional 15 min in order to get a full homogenization. After that the slag
was removed, and then the melt was poured at about 800 °C into a cylindrical
resin-bonded sand mold with dimensions of outer diameter (£100 mm), inner
diameter (£42 mm) and length (250 mm) which mounted on the ultrasonic sono-
trode of diameter (£40 mm) as shown in Fig. 1. The reason for using a cylindrical
resin-bonded sand mold is to reduce the cooling rate effect on the resulted micro-
structures of the prepared samples.
to the presence of coarse primary Mg
Mg Si [2–4].
Ca could modify and refine both the primary and eutectic Mg
in Mg–6Zn–4Si alloy [4] as well as eutectic Mg
Si alloy [5]. Recent research [2] has shown that the primary Mg
2
Si and the brittle eutectic
2
2
Si
Si
2
Si in Mg–5Al–1Zn–
1
2
could be effectively refined and modified by the application of
HIUST on the hypereutectic Mg–5 wt.%Si alloy during solidification
process. However, combined effect of HIUST and Ca addition on
The solidification characteristic of the prepared Mg–5 wt.%Si and Mg–5 wt.%Si–
0.3 wt.%Ca alloys was confirmed using thermal analysis. The thermal analysis test
sample was obtained by pouring the quantity of the melt at about 830 °C into
standard Qiuk–Cup resin-bonded sand cup with dimensions described in Fig. 2. A
high sensitivity type K thermocouple (chromel–alumel) located vertically at the
center of the cup, facilitated the capturing of the temperature during solidification.
The data for thermal analysis were collected using a data logger and transferred to a
personal computer for analysis. Thermal analysis trial was repeated three times to
ensure reproducibility and the accuracy of the results.
modification of primary Mg
tic Mg–Si alloys has not been reported. Therefore, the main aims of
2
Si and wear resistance in hypereutec-
⇑
925-8388/Ó 2014 Elsevier B.V. All rights reserved.
0