فهرست مطالب

نشریه ریخته گری
پیاپی 94 (زمستان 1388)

  • تاریخ انتشار: 1388/10/11
  • تعداد عناوین: 8
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  • M. Zandrahimi, E. Shakib, M. Hakimi Page 2
    Nowadays, the utilization of Aluminium alloys because of their low weight and good mechanical properties is rising. During the last few years the use of semi solid casting method, due to their superior mechanical properties has been growing. In this research, the effect of Si as well as the type of casting on the microstructure, wear resistance and hardness of Al-Si has been investigated.For this purpose, alloys with different amount of Si i.e., 4, 8 and 14% Si in three conditions, without stirring, with stirring (short and long stirring time) were cast. After casting, the samples were wear tested. The microstructure of all samples was examined with optical microscope and the worn surfaces were investigated by Scanning Electron Microscope. Results show that stirring the melt before casting causes the breaking of dendrites, which leads to globular structure and consequently increases the wear resistance of the material.
  • S. A. Azarmehr, M. Divandari, H. Arabi, B. Nayebi Page 11
    Molten Aluminum-magnesium alloys oxidize rapidly during casting and handling if adequateprevention measures are not taken. Oxide films that form in a very short time during pouring the melt into moulds seem to be one of the main reasons for dross-like defects, porosities and etc. The characteristics of these films in Al-1Mg and Al-5Mg were studied and compared with the results of similar researches published in literature. For this investigation, Samples of oxide–metal–oxide sandwich were prepared by the bubble impingement technique. Features such as thickness, size and morphology of the oxide film have been examined by SEM. Results show that thickness of oxide folding increase with increasing the magnesium content in Al-Mg alloys.
  • V. Joladi, A. Babakhani, S. M. R. Ziaei Page 22
    This study focuses on the effects of inoculation on the microstructure of ductile iron (nodurality, nodule count per unit area, the amount of ferrite and pearlite and variation of hardness). 0.1, 0.2, = 0.3, 0.4, and 0.5 weight percent of silicon carbide added to ductile iron in order to nomination inoculants’ s optimum amount. Also 0.5 weight percent of ferrosilicon for achieving desired mechanical properties have been used. Observation and experiments on the basis of complete solution at the time and temperature of inoculation treatment showed that adding 0.3% of silicon carbide as inoculants to ductile iron in compare with adding 0.5% ferrosilicon has a more positive effect on morphology and distribution of graphite nucleus in microstructure. More efficiency of SiC in inoculation is due to formation of clusters of dispersed carbon I melt that has a similar crystallography structure with graphite and these ease inoculation. Results also showed that decreasing cooling rate cause to increasing solidification time and as a result the effect of silicon carbide on inoculation will be decreased.
  • E. Parshizfard, M. Ghanbari, S. G. Shabestari Page 31
    In this research, the effect of plastic deformation and semi-solid forming of deformed structure on the microstructure of AlSi9Cu3 alloy containing 4 wt% of iron after 5, 10, 15% deformation in warm rolling process have been investigated. The deformed specimens were reheated at 580°C for 15 minutes in a resistance furnace and then thixoformed in the semi-solid state. Optical microscope images revealed that the size of intermetallic compounds was reduced and good distribution of these particles were seen after thixoforming in comparison with the as-cast microstructure. After 10 to 15% plastic deformation of the specimens and partial melting, the matrix is composed of spherical α-Al grains embedded in Al-Si eutectic structure and well-distributed fine intermetallicphases. Gag and shrinkage porosity were reduced appreciably after thixoforming.
  • A. Shahcheraghi, N. Eslamirad, R. Raiszadeh Page 39
    The deleterious effect of the submerged oxide films in liquid aluminium alloys on the quality of Al castings has been shown recently. Keeping the liquid metal, which is flowing from the pouring basin to the mould cavity, free from surface turbulence is the main duty of a good running system. Naturally-pressurized running systems have been introduced recently to provide the means to achieve this goal. The effect of overflow at the end of the runner in this running system has been studied in this study. The results showed that the overflow prevents the liquid metal from a sudden stop after reaching to the end of the runner. This prevents the back-pressure to build up in the liquid metal which is flowing in the runner, and hence, prevents the turbulent entrance of the melt into themould cavity. The experimental results are in good agreement with the simulation results obtained using SUT CAST fluid flow simulation software.
  • M. Arghyiani, M. Divandari, M. Azadbeh, M. Zarghami Page 44
    Lost foam casting has the capability of putting different types of fibers inside the polystyrene pattern before casting process which leads to production of composite. Furthermore, the process utilized in this research can be regarded as a promising approach for in mold alloying, and study of interfacial reactions between a given melt and supposed solid insert. In this study, Al wire was put inside the polystyrene pattern and then gray cast iron poured. The results show interesting effects of Al in cast iron. Microstructure and effect of Al in formation of different phases were studied by SEMand optical microscopes. Results show that Al affected graphite in gray iron. Graphite with small size and spherical shape formed. In addition, formation of different components from Fe-Al observed.
  • S. M. Madani, S. H. Razavi, H. Olya Page 51
    In this research the Air-Gap interface cast-metallic mold is determined using the electrical-capacity method. In this method the internal surface of mold and the outer surface of the cast is considered as capacitor plates and the Air-Gap between them is considered as capacitor dielectric and the Air- Gap thickness and the rate of change it with respect to time is obtained by a mathematical model. In this study the formation of the Air–Gap in cylindrical specimen of Al-12%Si Alloy in a low-carbon steel mold and in the gravity casting is investigated. The cylindrical specimen is 80 millimetres in diameter and 150 millimetres in height and the thickness of mold is 30 millimetres. In order to charging the electricity on the capacitor plates, electrical potential difference between the plates of the capacitor is induced by electricity and a RLC meter placed in the path of electrical current isused for measurement of the variation capacity capacitor. Based on the results it is investigated that as time of pouring increases the capacity of the capacitor and the Air-Gap decrease. As a result, thermal resistance oriented from Air-Gap because the heat transfer coefficient decreases intensity.
  • A. Behboud, M. Mazar Atabaki, Y. Kalantari, A. Dehghan Page 58
    In the present study, the effect of Ti on the castability of Al killed ultra low carbon (ULC) steel, and the possible reasons for the poor castability of the Ti bearing ULC steel Ti-free grades are investigated. In addition, suitable evaluations have been countered to prevent inclusion deposition in the submerged entry nozzles (SEN) during continuous casting of Ti bearing Al-killed ULC steels. Characteristics of inclusions in the submerged entry nozzle deposit and corresponding liquid steel and slag samples from VD degasser and tundish were investigated. The presence of small quantity of Ti-bearing alumina inclusion was identified to be responsible for the extensive melt freezing inside the SEN deposit and poor castability of Ti-bearing Al-killed ULC steels. The effect of all materials contacting liquid steel subsequent to the VD degassing, on the reoxidation behavior and castability of liquid steel, was measured from their chemical composition. The result of this studyshowed that whereas reoxidation is not enough for the castability of all Al-killed steels, it becomes inferior for Ti-bearing Al-killed steels. It is due to the formation of Ti-bearing inclusions that promote large-scale melt freezing inside the nozzle deposits.