Papers by Keyword: Al-Fe Alloy

Abstract: The present study investigated the laser welding performance of Al-Fe aluminum alloy sheets with different contents of intermetallic compounds. Under the same welding parameters, the alloy of higher intermetallic compounds content has wide and deep weld pools with uniform sizes. The alloy of lower intermetallic compounds content has narrow and shallow weld pools with nonuniform sizes. The higher content of intermetallic compounds results in higher laser absorptivity and lower thermal conductivity, and then increases the effective absorbed energy during welding, which is beneficial to the formation of wide and deep weld pools. The distribution uniformity of intermetallic compounds influences the size uniformity of weld pools. In the alloy with lower content of intermetallic compounds, the nonuniform distribution of intermeallic compounds results in the formation of abnormal weld pool, leading to the nonuniform size of the weld pools. In the alloy with higher content of intermetallic compounds, uniform distribution of intermetallic compounds make the size of weld pools more uniform.

Abstract: Cast AlFe alloys containing several percent iron have low ductility because of their brittle precipitates. Therefore, precipitate refinement is very important for improving their mechanical properties. In recent decades, severe plastic deformation processes have been developed to achieve this grain refinement. For example, our previously proposed severe plastic deformation process, called compressive torsion, is quite effective for not only grain refinement but also precipitate refinement even in brittle materials. In the present work, precipitate refinement of cast Al—Fe alloys by compressive torsion and the resulting improvements in their tensile properties were investigated. Compressive torsion with various numbers of revolutions was applied to Al—Fe alloys at 373 K. Then, the alloys were subjected to tensile testing at room temperature, 473 K, and 573 K. The obtained experimental results indicated that the initial eutectic microstructure of the alloys disappeared after the compressive torsion processing. All large precipitates with sizes of more than 200 μm were refined, and their sizes were reduced to several tens of micrometers. Furthermore, these refined precipitates were dispersed homogenously in the alloy microstructure. In result, the tensile properties of the alloys, namely, their strength and elongation, were improved remarkably. In particular, the elongation reached more than 30% at room temperature.

Abstract: In this work, three water-cooled experimental solidification devices were developed, and experiments were carried out with an Al-1.5wt%Fe alloy. The three experimental setups consist of vertical cylindrical steel molds with each of them having different zones cooled by water. For the inward solidification, a cooled tube is used having its upper and bottom part thermally insulated. For the outward solidification, a cooled tube, forming an inner part, is concentrically placed inside a cylindrical mold, which is thermally insulated from the environment, by using insulating materials. For the upward solidification, the bottom part of the mold is water-cooled and consists of a thin (3 mm) disc of carbon steel, whilst the cylindrical surface is covered with insulating material to avoid lateral heat losses. A numerical solidification model based on the finite difference method is applied for the simulation of the three aforementioned cases of solidification from the chilled surface considering transient heat flow conditions. Experimental thermal readings in the castings have been used for the determination of the transient overall metal/coolant heat transfer coefficient, h, through a numerical-experimental fit of casting thermal profiles based on inverse heat transfer calculations. It was found a significant variation of h as a function of time during solidification in the three cylindrical set-ups experimentally examined, including a remarkable increase in h during the outward solidification. Introduction

Abstract: Based on the empirical electron theory of solids and molecules theory(EET), the valence electron structures(VESs) of the strengthening phases Al₃Fe and Al₆Fe in Al-Fe alloy are calculated, then the stability of Al₃Fe and Al₆Fe, the precipitated sequence under the non-equilibrium solidification, the phase transition during aging and the effects of alloy elements are discussed. The results show that the values of covalent electron pairs on the strongest bond n₁, the total forming bond ability F, and the number of atom state group σ_N of Al₃Fe and Al₆Fe are bigger than that of Mg₁₇Al12 and Mg₂Si, so the stability of Al₃Fe and Al₆Fe is better. The total forming bond ability of Al₆Fe is far smaller than that of Al₃Fe, so Al₆Fe generates first under the equilibrium solidification. The strongest bond of Al₆Fe is weaker than that of Al₃Fe, so Al₆Fe is easy to be broken up and form the more stable Al₃Fe finally during aging. The addition of alloy elements changes the VES of Al₆Fe and makes its values of F, σ_N and n₁ increased, the stability of Al₆Fe is strengthened too, which delays the Al₆Fe→Al₃Fe transition and improves the transition temperature.

Abstract: The effect of DC gradient magnetic field and the sectional solidification on the structure of Al-Fe hypoeutectic alloy was investigated. The experiment results showed that the morphology and structure of the sample were homogenous, when it was bulk solidified without magnetic field. When the sample was sectionally solidified without magnetic field, the upper part had less iron content, bigger dendritic trunk and less interdendritic precipitate. When the sample was sectionally solidified in the gradient magnetic field, the above-mentioned differences between the upper and lower part were more prominent. The physical essence of the experiments was analyzed with quantum mechanics and solidification theory.

Abstract: Eight hypoeutectic aluminium alloys with iron content within the range of 0.07-1.09% by weight, were examined. The structure, the mechanical and electrical properties of wires used for electrical purposes were studied. The batch material for the drawing process was wire rod obtained from the continuous casting and rolling line by Continuus-Properzi method. It has shown a linear relationship between mechanical properties of wire rod, a higher plasticity of wire after drawing process and an increase in thermal resistance of the material with increasing iron content. The findings enable to draw conclusions of basic and application characteristics, pointing to the possibility of using aluminium with higher iron content in the wire drawing process of small diameter and microwires for the production of automotive bundles, accumulator cables and winding wires.

Abstract: The semi-solid compression behaviors and the microstructure of Al-Fe alloy prepared by electromagnetic stirred were investigated in the strain rate range of 5×10-3 s-1 to 5×10-1 s-1 and the temperature range of 610 to 640°C on INSTRON-5500R materials testing machine. The experimental results showed that, during the semi-solid deformation of Al-Fe alloy，the peak value of true stress decreased with elevating deformation temperature. As the deformation increased, the stress peak value of the high solid fraction alloy was tending upwards, and that of the low solid fraction was tending downwards. The peak increased with increasing the strain rate. Al-Fe alloy was sensitive to strain rate during semi-solid compression. The strain softening phenomenon would happen. The smaller strain rate, the longer softening process, the stress falling was more slowly. The strain softening was a reason that the semi-solid alloy structure was instability during deformation. The semi-solid deformational behaviors of Al-Fe alloy was bound up with deformation temperature, strain rate, and deforming extent.

Abstract: Upward directional transient solidification experiments have been carried out with an Al-1.0wt%Fe alloy. Tensile tests were carried out with samples collected along the casting length and these results have been correlated with measured cell spacings, since cellular growth has prevailed along the directionally solidified casting. The resulting mechanical properties include ultimate tensile strength, yield tensile strength and elongation. The used casting assembly was designed in such a way that the heat was extracted only through the water-cooled system at bottom of the casting. During non-equilibrium solidification, typical of DC (direct chill) castings, different cooling rates occur from the casting cooled surface up to the top of the casting, causing the formation of metastable intermetallic phases (AlmFe, Al6Fe, etc) in addition to the stable Al3Fe phase. The extensive presence of plate-like Al3Fe phase in the as-cast structure adversely influences the mechanical properties of Al-Fe alloys, since this morphology is more likely to induce microcracks than the fibrous Al6Fe phase. In order to permit an appropriate characterization of these intermetallic phases, they were extracted from the aluminum-rich matrix by using a dissolution technique. These phases were then investigated by optical microscopy and SEM techniques. It was found that the ultimate tensile strength, the yield strength and the elongation increase with decreasing cell spacing and experimental laws correlating cell spacing and these mechanical properties have been established.

Abstract: The aim of this work is to study the effect of a low frequency alternating magnetic field on morphology and distribution of A3F2 in the Al-2.89 wt.% Fe alloy. At the cooling rate of 0.05 °C/s, only Al3Fe phase was observed in the iron-containing intermetallics. It was noteworthy that, compared with the conventional solidification, the primary Al3Fe phase was refined and accumulated towards the center of the sample by applying the alternating magnetic field. This phenomenon is considered as the result of the larger Lorentz force acting on the Al3Fe phase than the Al matrix.

Abstract: Recently nanocrystalline Al-Fe alloys produced by a vapor quench method have been reported. These alloys are supersaturated solid solution and exhibit high strength with good ductility. It is postulated that the high strength of the Al-Fe alloys could be achieved by both the nano-grained structures and the solid solution strengthening. The contribution to the yield strength due to both the grain size strengthening and the solid solution strengthening were analyzed from the experimental data. Then the contribution to the yield strength due to the solid solution strengthening was estimated from the misfit strain calculated from the first principles in order to compare with analytical results estimated from the experimental data.