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Abstract
Our technological advancing society is continually challenging thelimits of conventional materials. Extreme and sometimes conflictingrequirements are forcing us to engineer materials not possible byconventional alloying methods. Metal matrix composite materials comeunder one class of engineered material developed specifically to meet this challengeIn the present work, Al/SiCp composites were prepared using powder metallurgy (PM) technique by consolidating Al powder with SiCp particles under a specific pressure (cold uniaxial compaction), and temperature
(sintering process) followed by secondary processing hot uniaxial
extrusion. The microstructure, mechanical, physical properties, and fracture
behavior of the resulting composites were also studied.
The Al powder with different volume fractions (0, 5, 10, 15) vol.%. SiCp
(average particle size of 7 μm) were mixed together. These were
consolidated under pressure of 600 MPa at room temperature (Cold Compaction) and sintered in muffle furnace at 550ºC for 6-8 hours. The produced compacts (discs with Ф50 mm diameter and 20 mm height) were extruded at temperature 400ºC with extrusion ratio 11.11.It was noted that the extrusion pressure increased with increasing the
reinforcement volume fraction and the length of billet. This is due to
increasing the frictional resistance. While decreased with increasing
extrusion temperature. This is due to increasing the frictional resistance. In
addition, the coefficient of friction increased almost linearly as
reinforcement volume fraction
The microscopic observations of Al/SiCp indicated that the SiCp
particles distribution in the sintered specimens was uniform. Except for that
15 vol.%, SiCp showed many clusters and agglomeration of particles than
III
other volume fractions. The extrusion microscopic observations indicated a
uniform distribution of SiCp particles in all volume fractions.
With increasing reinforcement volume fraction of SiCp particles, the
composite density increased. Density through the extrusion process was
higher than that of the compacted and sintered process. This is resulting
from reducing of the cracks, cavities, and pores of material due to higher
plastic deformation during extrusion process under high indirect
compressive stress, extrusion ratio, and extrusion temperature.
A smaller value of coefficient of thermal expansion (CTE) was found
for the composite with higher amount of SiCp reinforcement. This is due to
that increasing the amount of reinforcement increases the localized stresses
around the matrix particles (compressive stress) and that represents a
higher constraint of pure Al matrix, which leads to a lower CTE of
composite. CTE increased non- liner with increasing temperature and the
rate of CTE increasing is high up to 300°C and slightly decreases until
500°C.
The hardness increased by increasing the volume fraction along radial
and axial direction. This is due to transfer of applied load from the matrix
to the SiCp particles. Higher hardness of extruded than sintered specimens
along radial and axial directions is due to the strain field around the
ceramic particles (in matrix material), and decreasing the interparticle
spacing. In addition, the hardness along axial direction was higher than
along radial. This is attributed to the alignment of SiCp along the extrusion
axis.
The tensile, compressive yield strength and tensile modulus of elasticity
of the aluminum matrix increase as more reinforcement particles were
added. This is due to transfer of applied load from the matrix to the SiCp
particles.