الفهرس 
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Abstract
Aluminum alloy AA7075 is considered one of the commercial
aluminum alloys which is characterized by its light weight and the specific
strength (high strength to weight ratio), it is used widely in aerospace and
transportation applications. In the present work, green, novel, and energy
saving processing technique called Friction stir processing; (FSP) is used to
produce surface composite layer using the base material Al-7075 and
reinforcement particle of boron carbide (B4C). In the present investigation a
discussion is demonstrated to produce surface composite using combination
of different tool rotation speeds (400 and 600 RPM) and different number of
passes (one, two, three and four passes) for each rotational speed with a
constant travel speed (50 mm/min) and tilt angle of 3o
. The processed samples
were investigated through the microstructural analysis as optical microscopy
(OM), and scanning electron microscopy (SEM) equipped with EDS analysis.
Mechanical properties were conducted by using hardness test (Vickers) and
wear and friction tests using block on ring dry sliding test to study the wear
scar depth and the coefficient of friction (COF). This study displayed an
improvement of the hardness, wear and friction properties with increasing in
number of passes that is attributed to B4C particles dispersed in aluminum
matrix. The hardness increase from 67 HV1 (base material AA7075) to
maximum value 150 HV1 in the processed samples, higher coefficient of
friction in the friction stir processed samples as compared to the base material
from average value COF 0.6 (BM) to 1 (processed samples). The presence of
surface composite layer enhanced the hardness and wear resistance of Al7075.