الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Friction Stir Processing is used to develop local and surface properties in chosen locations of casting Al-Si alloy. In recent years; Friction Stir Processing (FSP) has been recognized as a successful approach for improvement of the corrosion resistance, microstructure and mechanical properties of cast Al- Si
alloys. In this study, the influence of friction stir processing process variables such as traverse feed rate, rotational speed and the type of pin profile tool (form and threaded cylindrical pin profiled tool geometry) has been examined on the
microstructure, macrostructure, corrosion resistance, hardness and wear behaviour of A356 cast aluminum alloy. FSP was conducted with five rotational speeds (355, 450, 560, 710 and 900 rpm); and three traverse feed rates of 10, 20 and 40 mm/min. Potentiodynamic polarization testing was conducted to determine the
corrosion properties of the base alloy and the FSPed samples. The samples
polarization test in 3.5 percent NaCl solution at ambient temperature. Wear tests were carried out under dry sliding conditions of the as-cast and FS processed alloy specimens using a pin-on-ring machine. Corroded and worn surfaces were investigated using a scanning electron microscope (SEM).
The results showed that with reducing tool rotational speeds resulted in
formation of basin-shaped stir zone of both the thread pin profiled tool and the form tool, while increasing rotational speeds of tool resulted in formation a ’top hat’ geometry which fabricated using form tool and resulted in creating of conicalshaped nugget zone with thread pin profiled tool. Parent material showed typical
dendritic structure compared to the stir zones, coarse Si particles are fragmented into fine globular silicon particles and distributed uniformly into α-Al matrix. The mean size and aspect ratio of the Si particles of nugget zone are significantly
affected by the rotation rate of the tool. The mean size and aspect ratio of the Si particles increases with increasing the rotation rate of tool. The base metal showed lower pitting corrosion resistance, hardness and wear resistance than the FS-v
processed specimens. General full-factorial design method has been carried out to
identify the significant parameters in FSP of cast Al-Si aluminum alloy in order to
determine the optimal response values, in addition to defining the optimum level for all of these parameters, also, regression model have been developed to predict the response. The correlation between the control factors and responses are established by analysis of variance (ANOVA), interactions plot and main effect
plot. It was found that, the most important parameter impacting pitting corrosion rate is the rotational speed, while the pin profile tool geometry has a second ranking parameter. The traverse feed rate has no statistical significant impact on
corrosion rate. In addition to, the form tool pin profile produces a better pitting
corrosion resistance of the stir zones compared to the threaded cylindrical pin profiled tool. Regression model was firstly used to develop the corrosion rate of FS processed A356 cast Al alloy. Then, the plotting of residuals versus fitted values
indicated a non-constant variance of this initial model. Box-Cox transformation was used to improve regression prediction model to the data and eliminate these drawbacks. The statistical analysis indicated that the most significant parameter
influencing wear resistance and hardness is the rotational speed, whereas the tool traversing speed has a second ranking. The pin profile tool geometry has no statistical important influence on hardness and wear rate. The quadratic regression model was used to predict the wear rate and hardness of FS processed A356 cast
Al alloy.