Al-Fe alloys are usually used as packaging and structural materials, but in the recent years, there have been considered for possible applications in aerospace field. The solidification sequence in pure aluminum containing 1 wt.% Fe is described in term of the formation of macrostructure, microstructure, microsegregation, porosity and mechanical properties. This material was studied in the upward unidirectional solidification system under transient heat flow conditions. Differences in microstructure, microsegregation, porosity and mechanical properties such as ultimate tensile strength, elongation and microhardness, due to the thermal parameter effects were observed and discussed. Experimental growth laws relating cellular spacing to the cooling rate and solidification speed have been determined, indicating that the increase in thermal parameter have induced a refinement effect on cell morphology. Microsegregation profiles of Fe solute were experimentally determined from the central region of the cell to the intercellular region under different solidification speeds. The Fe microsegregation determined from central region of the cell (FS = 0) to the intercellular region (FS = 1) show a growing profile, in any case considered. However, the profiles move upward with the increase in solidification speed, which indicates that Fe solubility in solid, increases with the increase in solidification speed. The effect of the solidification thermal parameters and cellular spacing on the porosity content were experimentally investigated. The value of porosity content increased along the casting. These results have pointed out that porosity content is affected by solidification parameters and cellular patterns. Further, measurable effects of the thermal parameters, cellular spacing and porosity content on the mechanical properties were experimentally determined. It stands out among experimental results the influence of porosity on the mechanical properties of as-cast material. In any case analyzed, mechanical properties increase with decreasing porosity content.

Abstract The solidification control is of extreme importance, because it strongly affects the final casting quality sanity. The structure obtained is generally not homogeneous and gives rise to great variations in composition, with position at small and large scales, which is known as segregation. An understanding of the way segregation occurs in continuous casting is of great importance for steels and in designing post-casting processes. As-cast structures are responsible the reduction in both scale and extension of segregation, because mass transport is dependent on the time required to diffuse a solute over a characteristic distance, e.g., the dendrite spacing that the characterizes the solidification structure. In this work, the effect of pouring temperature in steel slabs on the continuous casting processes are systematically investigated. Relationships between pouring temperature (PT) and center macrosegregation was qualitatively examined. Photomicrographs of specimen taken from transverse sections of steel slabs, shows that macrosegregation is strongly affected by pouring temperature (PT). For solute of carbon, phosphorus and sulfur, has been shown that the pouring temperature (PT) has a significant role on the resulting macrosegregation profiles, while that the elements as such silicon, manganese and aluminum, the said thermal parameter seems not able to affect its macrosegregation profiles. This is due to the fact that the solutes with lower partition coefficients favors segregation during the continuous casting process. It is shown for considered steels, the pouring temperature (PT) influences the position of the columnar to equiaxed transition (CET). Experimental results show that the end of the columnar region is abbreviated when lower pouring temperatures is used in continuous casting process. One can observe that as the pouring temperature (PT) increase in continuous casting process, the secondary dendritic arm spacing (λ2) increase, i.e., the dendritic morphology became coarsen.

Abstract Hypoperitectic Cu − 20 wt.% Sn alloy was solidified under different cooling rates and solidification growths using directional solidification system. The effects of cooling rate and solidification growth on the microsegregation profiles and tertiary dendritic arm spacing (λ3) were experimentally investigated along the casting. A mathematical model known as phase-field was applied to simulate microstructure and microsegregation during solidification in system Cu-Sn liquid. In this paper the applicability of the phase-field model to the solidification problem in a real alloy system was systematically explored. Microsegregation profiles and realistic dendritic structures were obtained using the phase-field model. The results calculated by phase-field model show various solidification features consistent with our experiment. The calculated tertiary dendritic arm spacing (λ3) and microsegregation profiles were compared with experimental values from directional solidification system. Since the calculated microsegregation profiles using the equilibrium partition coefficient (keq) can yielded discrepancies from the experimental results, an effective partition coefficient (kef) as a function of solidification growth, is proposed in phase-field model, showing a good agreement with the experimental data for any case examined.

Aluminium with silicon as alloying element, form a class of material providing the most significant part of all material casting manufactured materials. These alloys have a wide range of applications in the automotive and aerospace industries. It is widely recognized that moderate addition of silicon to aluminum, significantly improves the resulting mechanical properties. Hypoeutectic Al-Si alloys were used in the present experimental study to investigate the solidification parameters effect and Si 3-5 wt% addition on the microstructural features and resulting hardness in a vertical directional solidification system. The hypoeutectic alloys were directionally solidified under transient heat flow conditions in a range of cooling rates from 0.3 to 4 ºC/s. Characterization analyses by optical microscopy indicate clearly that secondary dendritic arm spacing (λ2) increases significantly with the decrease in solidification speed (SP) and cooling rate (Ṫ). On the other hand, experimental growth laws relating the secondary dendritic arm spacing (λ2) to the solidification speed (SP) and cooling rate (Ṫ) indicate that Si addition from 3 wt% to 5 wt% has induced a thickening effect leading to increase in λ2 . While, experimental results have shown that the resulting hardness increase as solidification processing parameters (SP and Ṫ ) increase. Results of Vickers hardness test for Al-5 wt% Si alloy has hardness increase of 18 % from that of Al-3 wt% Si alloy with mean values of 26 and 22 HV, respectively.