Papers by Author: S.G. Shabestari

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Authors: S.G. Shabestari, M.M. Hejazi, M. Bahramifar
Abstract: The effect of magnesium addition up to 0.9 wt.% on the microstructure and mechanical properties of Al-9Si-0.35Mn alloy has been investigated in both as-cast and heat treated conditions. Generally, Mg addition increases the heat treatability and strength of the alloys at the expense of the lower ductility. High levels of magnesium addition, causes the formation of large and brittle intermetallics, a slight increase in porosity and hence, a decrease in ultimate tensile strength and ductility of the cast alloys. T6 heat treatment increases the strength of the alloys up to 80 percent compared to as-cast samples. Among the studied compositions, heat treated Al-9Si-0.35Mn-0.25Mg alloy, has the maximum value of quality index and can be regarded as a promising material with the optimum mechanical properties for industrial applications.
Authors: S.G. Shabestari, M.M. Tavakoli, M. Ghanbari
Abstract: Al-Si-Fe alloys are a general purpose of die casting alloys, widely used to manufacture automotive parts. Forming this alloy in semi-solid state can eliminate important problems in die casting process. In the present work, low superheat melt was employed to produce modified microstructure and non-dendritic A380 alloy feed stocks. The melt was cast on a cooling slope plate at 615 °C to obtain ingots. Then, ingots are thixoformed using a hydraulic press after heating them at 570 °C for 15 minutes, yielding a microstructure with predominantly α–Al globules, Si particles, and modified β-phase intermetallic compounds. The effect of semi-solid processing on the morphology, size, and distribution of iron-bearing intermetallics was studied. The results of image analysis of the samples showed that by using semi-solid method, the shape factor of α-Al phase improved, and iron containing intermetallics were modified in size and distribution. These changes in the aspect ratio and redistribution of the intermetallics improved the mechanical properties such as hardness of the products.
Authors: S.G. Shabestari, R. Gholizadeh
Abstract: Dense precipitation of various intermetallic compounds is a common feature in the microstructure of Al-Si piston alloys. In this investigation, microstructure of LM13 alloy and three high Cu-containing Al-Si piston alloys with different amounts of Ni, Fe, and Mn were studied by means of optical microscopy (OM) and scanning electron microscopy (SEM). Chemical composition of the phases was determined by using energy dispersive X-ray analysis (EDX). The precipitation of the phases was studied through thermal analysis of the solidifying samples. Also, tensile properties and hardness of the samples were measured. The results showed that the various intermetallics such as Al12(FeMn)3Si2, Al3Ni, Al9FeNi, and Al3CuNi precipitated during the solidification. The high Cu-containing alloy with optimum levels of Ni (1.8 wt.%), Fe (0.75 wt.%), and Mn (0.3 wt.%) has the highest tensile strength (250 MPa) and hardness (110 BHN) among the other alloys.
Authors: S.G. Shabestari, P. Ghaemmaghami, H. Saghafian, A. Osanlo
Abstract: Attractive physical and mechanical properties of aluminum alloys make them very interesting for the automotive industry. The commercial way for manufacturing LM28 alloy is die-casting, but this process encounters several problems such as shrinkage and gas porosities. Their good mechanical properties and high resistance to wear are because of the presence of hard primary silicon particles distributed in the matrix. Therefore, the size and morphology of primary silicon and also the structure of α-Al particles in hypereutectic Al–Si alloys influence the mechanical properties of the alloys. In this research, a new process of manufacturing of this alloy has been developed using LM28 feedstock produced through cooling slope casting. The feedstocks produced via cooling slope casting had a partial globular structure that contained globules, rosettes and dendrites of α-Al. These feedstocks were thixoformed under three different pressures. The primary dendrites and rosettes changed to globular structure. The microstructure of thixoformed parts contained α-Al globules, small primary Si particles dispersed between these globules, and Al-Si eutectic phase. The mechanism of the formation of α-Al globules by this process was explained. Microstructures of as cast specimens, feedstocks produced via cooling slope, specimens that were heat treated in the semi-solid temperature and thixoformed specimens were studied with optical microscope and image analysis. The morphological changes during these processes were interpreted.
Authors: S.G. Shabestari, N. Wanderka, W. Seeliger, John Banhart
Abstract: Aluminium foam sandwich panels (AFS) made of a low-density aluminium alloy AlSi6Cu6 foam core and two dense 6082 alloy face sheets were fabricated, after which the panels were subjected to two different heat treatments. First, the AFS panels were aged to increase their strength without further solution heat treatment and fast quenching, a process which resembles a T5 treatment. Second, to define a reference point the face sheets of AFS samples were cut off the foam and subjected to a full T6 treatment. Hardness profiles were measured across the thickness of the face sheets after the two different treatments and the microstructure was investigated. The main conclusion is that mechanical performance of AFS panels can be considerably increased by heat treatment without full solution heat treatment (T5), but without reaching the level of a full T6 treatment. The potential use of an easy to apply T5 treatment is an important cost reducing factor.
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