فرخ گلستان نژاد

The shaping of Aluminum Alloys has always been considered. semisolid processes have been used to form these alloys for the last forty years. Among the different methods of semisolid processing, only thixocasting or thixoforming has been able to produce close to the final shape with these alloys, which due to low productivity and the need to use ticsotropic ingots with little industrial effect has not been encountered. The Controlled diffusion solidification Process (CDS) is an innovation in the production of wrought aluminum alloys in which, by mixing two melt with different thermal masses, non-dendritic microstructure is similar to that obtainable through semi-solid complex processes Is obtained. Despite its simplicity and high utilization, the use of this process requires an agreement between the maximum cooling rate and the complete mixing of the two melt. In order to study the effect of the cooling rate on this process and its optimization in the process of the CDS of the 2024 alloy, six cast-iron cylindrical molded castings with thicknesses of 2, 4, 6, 8 and 10 mm, under the same conditions, were casting in both conventional and CDS process. By inserting a thermocouple at a height and a certain distance from the mold wall, using the computer thermal analysis method, it was possible to record the cooling curve and measure the cooling rate. The structure of the samples was analyzed using optical microscopes (OM) an‎d scanning electron microscopy (SEM). The results indicate an increase in the likelihood of incomplete mixing with an increase in cooling rates. The best mixing method with a 1mm mold and cooling rate was 0.5 ℃ / s. Such a low cooling rate leads to increase the time of solidification and the formation of gas mixtures in the structure. In molds of 6 mm and 8mm with a cooling rate of 1.5 ℃/ s and 2.2 ℃ / s, a non-dendritic microstructure free of gas defects was observed. Elemental analysis of EDS showed that the CDS process has little effect on intermetallic phases. Keywords: Thixocasting, reocasting, Controlled diffusion solidification (CDS), Aluminum Alloy, Cooling Rate, Semi-Solid