FOUNDING RESEARCH JOURNAL
Year:2017 | Volume:1 | Issue:1 |Papers Count:7

The aim of the present study is to produce an in-situ Al matrix composite reinforced by iron-bearing intermetallics. Therefore, the effects of solidification parameters such as solidification rate (RL) and cooling rate (T) on the microstructural characteristics of a hypoeutectic Al-1.0%wtFe alloy during directional solidification have been investigated. The directional solidification process has been carried out using a Bridgman furnace having a water-cooled system at the bottom of the cold zone. The flow rate of the water was 1, 2 L.min-1 and the withdrawal velocity of the ingot was 1, 5, and 10 mm.min-1. Optical and electron scanning microscopy (SEM) have been used to study the microstructure of the samples. Cellular microstructure with the iron-intermetallic phases at the peripheral walls of the cells were found along the directional solidified samples. In order to characterize the intermetallic phases, the energy dispersive spectroscopy (EDS) was used. Al3Fe intermetallic compounds with the atomic ratio of Al and Fe (2.54:1) were found to be predominant. Cellular spacing (λc) was calculated in some sections from the bottom of chill zone. Variation of cellular spacing was plotted as a function of both solidification rate and distance from the bottom of chill zone. Hardness test was carried out on each cross-section and the hardness profile was plotted as a function of cellular spacing. The results showed that the hardness of Al-1.0%wt.Fe alloy was increased 1.12 times where the cellular spacing was reduced 22%.

In the current research, the effect of severe plastic deformation by multi-directional forging (MDF) and equal channel angular pressing (ECAP) on microstructure and mechanical properties of A520 Al-alloy was investigated. The samples which produced by ordinary and semisolid casting were processed by ECAP and MDF at room temperature (RT) and high temperature. The semi-solid process improved the formability of the alloy, such that the semi-solid specimens were ECAP and MDF processed up to 3 passes at RT without cracking, while the ordinary cast specimens were cracked at the first pass of MDF and ECAP processes at RT. The micro-hardness and shear punch tests showed increase the mechanical properties of the specimens, such that 3 passes of MDF and ECAP at RT increased the hardness of specimens from 60 to 128 and 137 HV and yield strength of specimens from 128 to 208 and 255 MPa, respectively. By increasing the ECAP temperature, the effect of ECAP on improvement of mechanical properties decreased considerably. The microstructural characterization by scanning electron microscope showed that the reason of mechanical properties improvement during ECAP and MDF processes lied in the grain refinement and modification of morphology and distribution of Al3Mg2, Mg2Si and AlFe precipitates during the processes. Comparison of ECAP and MDF processes revealed that the effect of ECAP process on microstructural modification and consequently improvement of mechanical properties was higher than that of MDF process.

In this study the graphitization characteristics were studied in the test bars produced by the in-mold lost foam (IMLF) process. Polystyrene patterns were prepared, and the test bars were produced in three different diameters. In this paper, only the microstructure of the test bars, having 10 mm diameter and 200 mm height, cast at two temperatures of 1410 and 1440oC, and 1 wt% of spheroidizing material (FeSiMg), have been investigated. For this purpose, 10 mm bars were cut from two sections, the middle and the end part (the furthest distance from the gate) and then, these sections were examined using optical microscope. The results show that, the melt temperature and fluid flow affect the graphite morphology as well as the distribution, shape, size and type of graphite. In the central part of the test bar, cast at 1410oC, non-spheroidal graphite is formed which are different from other areas, but at 1440oC, the graphite in the whole section is uniform and spherical, from the center to edge. The high nodule count (above 700 pcs. per unit surface) and above 80 percent nodularity, in both cases, are worth mentioning.

Slope cooling casting is one of the production methods in semi-solid state. Semi-solid processes led to reduce gas porosity and shrinkage and modify the structures. In this research, the effect of pouring temperature in slope cooling casting process and partial remelting temperature on microstructure and wear properties of Al-A390 alloy have been investigated. In this regard, casting was performed at 5 different pouring temperatures on a sloping surface with the constant length of 500 mm, angle of 45° and mold temperature of 450oC. Then, the partial remelting process was carried out at 3 different temperatures with a constant time. The results show that the suitable condition in view of the particle non-dendritic and the high hardness is achieved at the temperature of 590oC on the slope cooling with the length of 500 mm and the angle of 45o. In examining of the effect of the partial remelting temperature, the sample kept at temperature of 545oC for 30 minutes, compared to samples with partial remelting temperature of 555oC and 565oC, has a finer and more uniform grain structure. So that, the hardness and the weight loss at this temperature were obtained about 130 HB and 0.0193 gr. The hardness and wear resistance of this sample in comparison to sample without partial remelting increased 30 and 43 percent, respectively.

In the present study, an investigation of coefficient of thermal expansion, elastic modulus, yield strength of compression, wear resistance and hardness of 3 layers called inner, intermediate and outer are investigated for functionally graded Al based cylindrical shell containing 26 wt.% Cu and 8 wt.% Si. The microstructure is studied by using TESCAN MIRA3 field emission scanning electron microscopy (FESEM) and TITAN scanning transmission electron microscope (STEM) is revealed that intermetallic compound content reaches its maximum volume fraction at the inner layer with 33.3 Vol.% and then reduces gradually to 26.4 Vol.% at outer layer. In addition, wear rate was 5.4gr/m2 and hardness was 153 HV at inner layer and then gradual increase by 7.07 gr/m2 and decrease by 149 HV, respectively at outer layer. Moreover, the value of yield strength of compression is determined 275, 460 and 415 MPa at outer, intermediate and inner layers, respectively.

The effect of alumina nanoparticles contents with the average size of 40 nm on the microstructure and wear behavior of A356/Al2O3 nanocomposite produced through stir casting was studied. The alumina nanoparticles with the amounts of 1, 1.5 and 2 weight percent, were incorporated into the molten matrix alloy being mechanically stirred, along with blowing an inert gas. To improve the nanoparticles wettability, 1wt% Mg was added to the molten matrix alloy. The microstructure of the nanocomposite was studied by using optical and scanning electron microscopes. The microstructural observations showed that the alumina nanoparticles have been evenly distributed within the matrix. The percent of porosity measured by the Archimedes method is increased with increasing the nanoparticles weight percent from 1.3% to 3.2 %. It was shown that, the increased percent of porosity can be attributed to the increase in the particles agglomeration with increasing particles weight percent. To study the wear behavior of the materials, nanocomposite containing 1wt% alumina, having the lowest porosity percent and even distribution of nanoparticles, was selected. The wear test showed that the addition of nanoparticles to the matrix alloy gave rise to enhance its wear resistance. Study of the worn surfaces and sub surfaces showed that the dominant wear mechanism for the materials used in the current work is probably an adhesive wear followed by the formation of a mechanically mixed layer (MML). However, this mechanism occurred with the less wear rate for the nanocomposite as a result of the presence of reinforcing particles.