پژوهشنامه ریخته گری
سال پنجم شماره 1 (پیاپی 16، بهار 1400)

The structure of metals strongly depends on solidification parameters such as cooling rate and supercooling. It is obvious that the cooling rate is an important factor in order to refine metal structure, and especially affecting mechanical properties of metals. In this investigation melt spinning method is used to reach rapid solidification and ribbon shaped samples in Aluminum 5083 alloy were produced. The resulting ribbon samples were studied by optical microscopy (OM), scanning electron microscopy (SEM), micro hardness tester, X-ray difractometry, and were compared with their ingot counterparts. The results perfectly shown that the produced ribbons exhibits unique properties such as enhanced solid-solubility level of elements in the Al matrix (solid solution strengthening) and formation of spherically shaped intermetallic phases rich in Fe, Mn and Si and less than 50 nm in size homogenously dispersed in Al matrix which resulted in mechanical properties improvement and microstructural refinement of Al5083 alloy. As an example microhardness was approximately raised over 2 times more than conventional casting methods.

The 2024 aluminum alloy slab is usually produced at industrial scale with precise control on the solidification parameters using modern machines and undergoing extrusion process after casting in to eliminate the casting structure and increase the quality of the slab. The purpose of this research is to provide directional solidification in the 2024 aluminum alloy slab to control the mushy solidification and improve the rollability. For this reason directional solidification is used to eliminate the casting defects and to obtain thermal gradient between the riser and chiller. After studying on the effect of solution treatment T4 on the microstructure of the produced slab the possibility of avoiding rolling defects such as alligator cracking was studied and was optimized using simulation. The obtained results showed that with the feeder/sample ratio of 0.35 and the use of a suitable chiller, the directional solidification of Al2024 alloy can be obtained with minimum casting defects. Also study on the macrostructure and microstructure before and after solution treatment showed that a significant difference in the increase of the homogenization can be obtained by applying the applied thermal treatment. Furthermore the hardness of the solution treated sample is 30 percent less than of the as-cast sample which is due to the grain growth after thermal treatment and the elimination of the intermetallic phases of higher hardness. Also it was shown that the possibility of improving the rollability and avoiding rolling defects specially alligator cracking is possible using the suitable conditions of directional solidification and thermal solution.

In this paper, the effects grain refiner amount and its addition method and the wall thickness on the solidification microstructure ‎of austenitic granular cast iron with 5 weight percent manganese were investigated. For this purpose, the inoculation was ‎performed with ferrosilicon zirconium after spheroidizing with ferrosilicon magnesium. The grain refiner additions were ‎performed using two basic method, ladle inoculation and pouring stream inoculation in different amounts (0, 0.1, 0.2 and 0.3% ‎by weight). In addition, the casting process was performed in the step form sand-sodium silicate binder mold with 5, 10 and 20 ‎mm thicknesses. Microstructural evaluations and hardness measuring were achieved using the optical and electron microscopes, ‎EDS, MIP4 visual analysis and Rockwell C test method. The results showed that the as cast microstructure of the cast iron ‎consists of granular graphite and eutectic carbide at the pearlitic matrix. The amount of eutectic carbides and graphite nodule ‎count increase and the amount of pearlite and the size of the graphite’s decrease by decreasing the mold thickness. For all wall ‎thicknesses, the inoculation process decreases the amount of eutectic carbide and graphite size and increases the graphite nodule ‎count and its volume fraction. In addition, it was observed that the pouring stream inoculation is more effective than the ladle ‎inoculation. ‎

In the present study, the effect of Ti and Nb microalloying elements on the microstructure and mechanical properties of the quench-partitioned (Q-P) steel was investigated. The samples containing Ti and Nb micro-alloying elements were subjected to Q-P heat treatment and quench-Tempering (Q-T). After Q-P and Q-T heat treatment, the properties of the samples were examined by scanning electron microscopy (SEM), X-ray analysis (XRD), microhardness, tensile tests and. The results showed that Q-P heat treatment of both sample has better mechanical properties compared to Q-T heat treatment. In the Q-P heat treatment, the amount of retained austenite (γR) for the sample containing Ti is higher than that of the sample containing Nb. Fracture strength and strain of the sample containing Ti were recorded 1070 MPa and 24%, respectively. The fracture strength and strain of the sample containing Nb were also recorded 980 MPa and 19%, respectively. In Q-P heat treatment, the plasticity of the sample containing Ti microalloy is higher than that of the Nb microalloy sample.

Phase diagrams are one of the main tools in designing engineering alloys. The calculation of phase diagrams using computational thermodynamics has been of great interest to materials scientists in recent decades. Efforts in the last decades have led to the development of various algorithms for calculating phase diagrams. However, many of the proposed algorithms are either very complex or have limitations in calculating phase diagrams. High computational cost, errors in calculating miscibility gap areas, and inability to distinguish meta-stable equilibrium from stable equilibrium are just some of the limitations of existing algorithms for calculating phase diagrams. Therefore, optimization of existing algorithms or development of new algorithms for calculating phase diagrams has always been of interest to scientists. In the present study, the possibility of using the Jarvis March algorithm to calculate phase diagrams has been investigated. The Jarvis March algorithm is a well-known algorithm in computational geometry for calculating convex hulls. The results show that the proposed algorithm can be successfully used to calculate phase diagrams. The Simplicity of implementation and low computational cost are the main features of the proposed algorithm.

In the current study the microstructure and mechanical properties of Al-2Ni-xMn alloys was investigated as a substitute for Al-4Ni alloys. To this end, different melts containing 2 wt. % Ni and 1, 2, and 4 wt. % Mn were solidified at two cooling rates of 3.5 and 10.4 C/s. According to the results, under the low solidification rate, the tensile strength, fracture strain, and toughness of Al-2Ni-1Mn alloy are lower than those of Al-4Ni alloy by 26, 115, and 137%, respectively. However, further Mn addition impaired the tensile properties. Increasing the solidification cooling rate decreases the size and improves the distribution of Ni(Mn)-rich compounds and porosities within the microstructure and reduces the sizes of secondary dendrite arm spacing and grains. This substantially improved the mechanical properties of Mn-rich alloys. For instance, compared to Al-4Ni alloy solidified at 3.5 C/s, the tensile strength, fracture strain, and toughness of copper mold cast Al-2Ni-1Mn alloy increased by 50, 200, and 330%, respectively.