Abstract:
Cast aluminum-based metal matrix composites were prepared by adding different
weight percents (5%, 10% and 15%) of silicon carbide (SiC) particles to LM25
master alloy using a stir casting method. Different process parameters, viz., rate of
particle addition, stin-ertype and size, stirring time and temperature of the melt were
varied to get uniform distribution of particle in the composites. The casting -quality
was observed physically alter removal from the metallic mold.
Samples of 10em cube wcre preparell from the alloy materials for ageing treatments.
The samples were solution treated at 50O:t lOe for S hours and followed by water
ljllenchlllg at 15:!:SOc.Then thc samplcs were aged al 175:t lOe for periods ranging
from I to 10 hours, Peak aging was determinell by thc measurement of
microhardness of the matrix altoy using a Shimudzu microhardncss tester. The
microstmclure of the composites were investigated by optical and scanning electron
nncroseopc_
The machining characteristics of unreinforced LM25 alloy and lSwt% SiC
rcinforeed LM25 alloy wcre studied at different velocity and depth of cut by using a
lathe maclune. Carbide amI high speed stecl were used as cutting tool and the tools
tips were studied after the maehimng tests by optical microscopy.
Wear tests of as cast and peak aged of all [our materiats were conducted under dry
sliding conditions using a pin-on-disc type wear testing machine against hardened
high carboll steeL Thc wom surfaces were investigated by optical microscopy.
it was fOl.llldthaI the particle distribution is reasonably good in all the composites,
But, a noticeable porosity ill the composites was observed. The content of the
porosity increases with the increase of particle volume fraction. There have been
foun'\ a clear effect of differcnt process parameters (particle addition rate, stirring
lime etc.) Oilthe distributioll of particles and porosity in as-cast matcrials,
During machining of unreinforced all(lYboth the carbide and high speed steel toots
were fOllildmore resistance to wear than that of Al composites machining. The
carbide tool was shows lower wear loss than the high speed slecl 1001 during
machining of Al composites.
From the aging behaviour, il was found that the peak aging time become shorter with
the increase of particle eOlltent in the composites. All as-cast composites show the
lowcr wear resistanec than the as-cast unreinforced alloy. Among the three
composites with higher particle content show higher wear resistance than the
composites with lower particle content. Similar wear behavior,was found in .case of
peak aged condition.
