A comprehensive understanding of melt quality is of paramount importance for the control and prediction of actual casting characteristics. Among many phenomenon that occur during the solidification of castings, there are four that control structure and consequently mechanical properties: chemical composition, liquid metal treatment, cooling rate and temperature gradient. The cooling rate and alloy composition are most important among them. This paper investigates the effect of the major alloying elements (silicon and copper) of AlSi-Cu alloys on the size of secondary dendrite arm spacing. It has been shown that both alloying elements have reasonable influence on the refinement of this solidification parameter

The quality of the squeeze castings is significantly affected by secondary dendrite arm spacing, which is influenced by squeeze cast input

parameters. The relationships of secondary dendrite arm spacing with the input parameters, namely time delay, pressure duration, squeeze

pressure, pouring and die temperatures are complex in nature. The present research work focuses on the development of input-output

relationships using fuzzy logic approach. In fuzzy logic approach, squeeze cast process variables are expressed as a function of input

parameters and secondary dendrite arm spacing is expressed as an output parameter. It is important to note that two fuzzy logic based

approaches have been developed for the said problem. The first approach deals with the manually constructed mamdani based fuzzy

system and the second approach deals with automatic evolution of the Takagi and Sugeno’s fuzzy system. It is important to note that the

performance of the developed models is tested for both linear and non-linear type membership functions. In addition the developed models

were compared with the ten test cases which are different from those of training data. The developed fuzzy systems eliminates the need of

a number of trials in selection of most influential squeeze cast process parameters. This will reduce time and cost of trial experimentations.

The results showed that, all the developed models can be effectively used for making prediction. Further, the present research work will

help foundrymen to select parameters in squeeze casting to obtain the desired quality casting without much of time and resource

consuming.

In this study, the effects of grain size refiner addition and various pre-heating mold temperatures on AlSi9 cast alloy microstructure and solidification have been evaluated. For different process conditions, thermal analysis was performed for all samples and cooling curves were established. Important parameters in liquidus and eutectic Si-phase regions have been calculated using the first derivative cooling curves. Secondary Dendrite Arm Spacing (SDAS) variation was also determined. Experimental results question the effectiveness of cooling curve parameters in providing the microstructure data as a function of refinement. The present work shows that the effect of grain refiner addition on the value of SDAS was higher when the solidification time was lower. It indicated that the solidification parameters such as nucleation temperatures of α-Al phase, undercooling temperature and total solidification time were affected by grain refinement. It has been found that the addition of grain refiner affect the eutectic phase formation time. However, it has no effect on the eutectic phase morphology.

What is the limit of improvement the structure obtained directly from the liquid state, with possible heat treatment (supersaturation and aging)? This question was posed by casting engineers who put arbitrary requirements on reducing the DAS (Dendrite Arm Spacing) length to less than a dozen microns. The results of tests related to modification of the surface microstructure of AlSi7Mg alloy casting treated by laser beam and the rapid remelting and solidification of the superficial casting zone, were presented in the paper. The local properties of the surface treated with a laser beam concerns only a thickness ranging from a fraction to a single mm. These local properties should be considered in the aspect of application on surfaces of non-machined castings. Then the excellent surface layer properties can be used. The tests were carried out on the surface of the casting, the surface layer obtained in contact with the metal mould, after the initial machining (several mm), was treated by the laser beam. It turned out that the refinement of the microstructure measured with the DAS value is not available in a different way, i.e. directly by casting. The experimental-simulation validation using the Calcosoft CAFE (Cellular Automaton Finite Element) code was applied.

One of the most important factors directly affecting microstructure and mechanical properties in directional solidification process is secondary dendrite arm spacing (SDAS). It is very important to measure the SDAS and examine the factors that may affect them. To investigate the effect of growth rate on the SDAS, the alloy specimens were directional solidified upward with different growth rates ( V = 8.3-83.0 μm/s) at a constant temperature gradient ( G = 4 K/mm) in a Bridgman-type growth apparatus. After the specimens are directionally solidified, they were exposed to metallographic processes in order to observe the dendritic solidification structure on the longitudinal section of the specimens. Coarsen secondary dendrite arm spacings (λ _2C) were measured excluding the first arms near the tip of the dendrite. Local solidification times ( t_f) were calculated by ratio of spacings to growth rates. It was determined that the t_f values decreased with increasing V values. The relationships between t_f and λ _2C were defined by means of the binary regression analysis. Exponent values of tf were obtained as 0.37, 0.43, 0.46 and 0.47 according to increasing V values, respectively. These exponent values are close to the exponent value (0.33) predicted by the Rappaz-Boettinger theoretical model and good agreement with the exponent values (0.33-0.50) obtained by other experimental studies.