پژوهشنامه ریخته گری
سال دوم شماره 4 (پیاپی 7، زمستان 1397)

Two alloys of Al-Zn-Mg-Cu with the same amount of zirconium and different amount ‎of scandium (0.05 and 0.1 wt.%) were melt in the resistance furnace and cast in the cast iron mold ‎and, after doing the tests of ICP, Spectroscopy and DSC, were put under homogenizing, ‎solubility and T6 treatments operations. Using microscopic observations and DSC analysis, the ‎temperature and time of homogenizing the alloys samples were 500°C‏ ‏and 12h and, 490°C and ‎‎12h for Al-Zn-Mg-Cu-0.1Sc-0.09Zr and Al-Zn-Mg-Cu-0.0.05Sc-0.09Zr, respectively. At the ‎dissolution temperature obtained from the results of hardness test and microscopic ‎observations by FESEM, the alloys were subjected to dissolution and then, were put under T6 ‎thermal operations at 120°C for 12 hours. Microscopic investigations showed that the ‎dominant phases in the microstructure of casting were along with T (Al2Mg3Zn3 and copper solid ‎solution and MgZn2 phase, and the eutectic phase formed 10% of the microstructure. Also, ‎investigation of the casting and homogenized microstructure revealed that no phase included ‎scandium and zirconium in the microstructure. After the homogenization ‎operation, the eutectic phase decreased to 3%. The dominant phase observed in the ‎homogeneous microstructure was the phases containing iron. After the dissolution, the volume ‎fraction of the eutectic phase remained constant and the MgZn2 phase. Having performed the ‎T6 thermal operation at 120°C, Al3(Sc,Zr) and MgZn2 nanoparticles were observed at the ‎grain boundary and inside the microstructure.‎

The optimal quality of continuous casting is always one of the main concerns in the steel industry. ‎Copper mold is one of the main components of the continuous casting of steel. The physical, chemical and ‎mechanical phenomena that occur in the near-meniscus region play an important role in the surface ‎quality of the ingot. In this paper, several effective parameters including the effect of lubrication on the ‎mold surface, the formation of the meniscus and the formation of a specific type of galvanic cell on the ‎quality of the ingot have been investigated. According to the theory of molten ionic structure and ‎analysis of metallurgical slag, it can be said that the molten slag phase of the mold powder is an ionic ‎liquid (copper/iron), so that in the powder produced by stollberg, the force is driven to 1.9 volt. Based ‎on the cooling parameters of the copper mold, a three dimensional calculation model was created and a ‎three dimensional temperature, stress and thermal strain distribution was simulated numerically using ‎the finite element method (FEM) and the maximum deformation of the copper mold was about -0.04 ‎mm, The highest internal temperature of the copper tube is 2200°C and the maximum thermal stress of ‎‎390MPa. Based on the results, the largest difference in temperature from top to bottom of the mold is ‎not more than 10 degrees, and the maximum thermal deformation of the copper mold appears at a ‎position 30 mm below the meniscus, but not strong enough to cause cracking. In addition, the effect of ‎powder with different alkalinity on the characteristics of the oscillating marks on the surface of the ‎ingot was considered. Based on microscopic images of oscillation symptoms, it can be said that the use ‎of Scorialit powder makes the swinging signs shorter and with a lower depth than using the Accutherm ‎powder.‎

The purpose of this study was to investigate the microstructure, hardness and wear resistance of lightweight 3000 series Al functionally graded tube containing 2.3 wt.% Li at the inner, middle and outer layers. For this purpose, an Al-8.1 wt.% Si-2.7 wt.% copper- 2.3 wt.% Li tube fabricated at a pouring temperature of 750°C and a final rotation of mould at 1000 rpm by using a horizontal centrifugal casting machine. Mould was preheated up to 150°C. Microscopic evaluation has been carried out by using VEGA2 scanning electron microscopy; micro-hardness evaluation has done by using Vickers method at 50 gr and evaluation of wear resistance has been carried out by using a pin on disc method under a stress of 7.6 MPa in a distance of 1000 m. The results indicated that the amount of Li, Si and Cu has gradually increased from the outer surface to the inner surface of the tube. Also, the sum of the existing phases in the matrix, such as β-intermetallic compounds (ie, AlxLi, AlSi and Al2Cu) has increased from 17 vol.% to 35 vol.% at the outer surface to the inner surface of the tube. For this reason, the hardness has increased from 95 HV at the outer surface to 251 HV at the inner layer. As a result, the wear resistance of the inner surface has increased 18 percent over the outer surface.

In this research, the effect of various amounts of aluminum on microstructure and ‎matrix hardness of ductile cast irons produced by in-mold casting process is investigated. ‎For this purpose, spherical graphite cast iron containing 3‎‏.‏‎7, 6‎‏.‏‎4 and 7‎‏.‏‎5 wt. % aluminum, ‎respectively, were prepared in Y-block form via in-mold process. After casting, samples ‎were prepared for microstructural studies, using conventional methods, and then were ‎examined by optical and scanning electron microscopy. Chemical composition of samples ‎was determined using optical emission spectrometry (OES), X-ray fluorescence (XRF), and ‎carbon-sulfur analyzer (LECO) method. X-ray diffraction test (XRD) was used for phase ‎identification. The results indicate changing of the precipitated pearlite morphology as the ‎aluminum content increases. Also pearlite and ferrite hardness increases, 178 and 164 ‎Vickers, respectively, as a result of increasing aluminum content from 3.7 to 7.5 wt. %. ‎Increasing the number of nodular graphites from 422 to 668 per square millimeter, reducing the graphite diameter from 13.1 to 8.8 micrometers, and changing the percentage of spherical graphite from ‎‎60 to 48 percent, with increasing aluminum content, are other noteworthy results.‎

In this study, effects of main squeeze casting parameters, including squeezing pressure, super-heat ‎and the duration of pressure on the microstructure, mechanical properties and wear behavior of A356 aluminum alloy ‎were investigated. For this purpose, the parameters were evaluated in three levels on the hardness, yield strength, ‎ultimate tensile strength, elongation and weight loss were examined. Squeeze casting process was performed using 20 ‎Ton hydraulic press equipped with a tool steel die having cylindrical cavity. Microstructural studies were evaluated by ‎optical and electron microscopy.  The wear test was performed by a pin on disk unit to 2000m wear distance at constant ‎condition. The results showed that the squeezing pressure causes the alpha-aluminum dendrites and eutectic cells to be ‎finer in the microstructure and reduce the casting defects. Also, the squeezing pressure, the duration of pressure and the ‎super heat, have the most influence on the mechanical properties and wear resistant, respectively. By increasing the pressure ‎from 60 to 90 MPa and above, the adhesive wear- mechanism is weaker compared to the abrasive and the wear type is ‎found to convert the low stress wear from high stress state, which improves the wear resistance. At least 90 MPa ‎squeezing pressure, at least 30 seconds duration for applying the pressure and a super-heat of 50 to 100 °C are the ‎recommended ranges for achieving the best wear resistance and mechanical properties.‎

Semi-solid processes are amongst the novel methods of producing materials. The first method of these processes is introduced around 30 years ago. These methods include forming of a semi-solid, semi-molten mixture which can be produced by using casting or mechanical forming techniques. The key point for using these fabrication processes is to create a non-dendrite structure in a semi-solid mixture. Some tools and devices have introduced in semi-solid casting until now for example cooling slopes, mechanical vibration device and melt mixers. These devices are usually used for the purpose of reducing the grain size and also increasing the mechanical properties of alloys. Also, some studies approved that using of the controlled atmosphere reduces the amount of impurities and porosities into the product. Therefore, in this paper, the effect of different conditions on A380 aluminum alloy is investigated using a mechanical vibrator that capable of controlling the atmospheric environment. In following, Taguchi statistical method was used to analyze the data and also reduce the number of experiments. The statistical results showed that the temperature parameter had the highest effect, equal to 64%, in this alloy. Also, the second level of this parameter, which is 625°C, was selected as the most appropriate level. Also, vibration frequency, with an effect of 32%, ranks the second position and vibration time with an effect of 3% is in the third place, which both perform best at their highest chosen level.