Mechanical Properties and Microstructures of Al-Fe Alloys Processed by High-Pressure Torsion

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INTRODUCTION

ALUMINUM (Al) alloys have gained widespread use in modern engineering applications due to several advantages, such as weight reduction and good ductility, but especially due to the increase in strength when combined with other elements as Mg, Si, Cu, and Zn. This has been possible by the use of traditional methods such as work (deformation) hardening, solid-solution hardening, grain reﬁnement, and ﬁne dispersion of precipitate particles.[1,2] However, for the case of iron (Fe), its application to commercial Al alloys is limited. Often considered one of the most common impurities due to its general abundance, Fe appears as a leftover during production, casting, and other processing techniques.[3] Its common use in devices and components increases the contamination of Al with Fe during recycling.[3,4] According to the equilibrium condition, the solubility of Fe in Al is very low (99.9 pct) through 53 lm mesh, and then they were manually agitated for 5 minutes. Designated compositions of the powders were determined by using an electronic scale with the following Fe contents: 0.5 pct, 1 pct, 2 pct, and 5 pct. A suﬃcient amount of the powder mixtures was then placed between the upper and lower anvils in the HPT facility

Fig. 1—Appearance of powder sample after HPT processing for N = 1 revolution. No visible diﬀerences are observed between bulk and powder samples after HPT.

Table I. Material Al-0.5 pct Fe Al-1 pct Fe Al-2 pct Fe Al-5 pct Fe

for direct consolidation at room temperature. Each anvil has a shallow circular cavity with 10 mm in diameter and 0.25 mm in depth at the center of the anvil. Figure 1 shows the appearance of a disk sample consolidated after HPT processing for 1 revolution. Density measurements were carried out using an Archimedes technique to validate the eﬀectiveness of the consolidation process. The thickness of the samples after HPT is 0.7 ± 0.1 mm, given that some material ﬂows out of the cavity during the HPT processing. Bulk material was supplied by Kobe Steel, Ltd. (Tokyo, Japan) in the form of extruded rods measuring 20 mm in diameter. These rods were obtained by extrusion from cast ingots with 155 mm in diameter and 200 mm in length at an extrusion speed of 2 mm/minutes at 723 K (450 C). The ingots have four diﬀerent nominal weight fractions (0.5 pct, 1 pct, 2 pct, and 5 pct Fe), and they were veriﬁed using inductively coupled plasma atomic emission spectroscopy, including the analysis of other impurities. Table I summarizes the chemical compositions of the cast samples used in this study. The 0.5 pct and 1 pct samples are hypoeutectic, whereas the 2 pct appears to be well within the eutectic composition.[3] The Al-5 pct Fe material had a ﬁnal composition of 3.72 pct, which is below the nominal value. However, this sample is well in the hypereutectic range, and for practical purposes, it will be compared to its powder counterpart, taking into account the slight diﬀerence in the Fe content. For HPT processing, the rods were ﬁrst sliced into disks with 0.9 mm thicknesses using

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