Enhancement of properties in cast Mg–Y–Zn rod processed by severe plastic deformation
Introduction
Addition of rare-earth (RE) elements is known to increase the strength and to improve the creep properties of magnesium alloys at high temperatures due to the formation of intermetallic phases [1], [2], [3], [4]. Most RE-containing magnesium alloys show an excellent precipitation hardening response [1], [2], [3], [4]; however, Mg–Y–Zn ternary alloys are not precipitation hardenable [5]. Superior mechanical properties in these alloys are achieved by other techniques, for example, warm extrusion of rapidly solidified powder (strength of up to 600 MPa and 5% tensile ductility) [6], [7], or working of cast billet [8], [9], [10], which results in strengthening by grain refinement. The microstructure after such processing usually contains a mixture of nano-scale magnesium grains (100–200 nm) and intermetallic particles that exhibit a range of long-period stacking-order (LPSO) structures, among which 18R and 14H are the most common [11]. The notation used to designate the LPSO intermetallic phases is defined in Ref. [11]. A unique feature of such LPSO structures is their lamellar morphology that comprises alternating layers of magnesium and intermetallic lamellae. The accumulated experimental evidence indicates that mechanical properties of the Mg–Y–Zn alloys can be tailored by proper control of the volume fraction and size of the lamellae of the LPSO structures. It is expected that an ultrahigh strength alloy may be obtained if a nano-scale distribution of LPSO structures is achieved.
It is not possible to achieve a redistribution of LPSO structures by deformation with conventional metal forming processes, as they have a geometrical limitation on the amount of strain imparted to the material. However, by severe plastic deformation (SPD) methods [12] a billet can be subjected to virtually unlimited strain without a change in its shape and dimensions. The most well-known SPD methods are equal channel angular pressing (ECAP) [13] and high pressure torsion (HPT) [14]. The effects of SPD on the mechanical properties of Mg–Y–Zn alloys have not been explored to date. It can be expected, however, that severe plastic deformation may lead to much finer grains and potential dispersion of the LPSO structures, and therefore much higher yield strengths. A comparative study of microstructure and properties of Mg92Y4Zn4 cast billets severely deformed by different SPD techniques has been performed in this work.
Section snippets
Materials and experimental methods
Mg92Y4Zn4 (composition in wt%) billet was prepared by permanent mould casting followed by homogenisation for 24 h at 450 °C in a muffle furnace. After homogenisation the samples were quenched in water to 70 °C. Cast billets were subjected to severe plastic deformation by three different routes, namely ECAP, HPT and ECAP followed by HPT.
Samples 10 mm in diameter and 37 mm in length were machined from the homogenised billet. Four passes of ECAP (route BC in which the specimen is rotated by 90° about
Microstructure
The microstructure of the as-cast alloy contains a large volume fraction of relatively fine-scale lamella (Fig. 2a) which are reported to have high concentrations of yttrium and zinc [5]. This microstructure is quite different from that normally observed in as-cast Mg-alloys which typically consist of magnesium grains and secondary phases in grain boundaries. This lamellar structure represents a mixture of 18R and α-Mg phases [5], [11], [15], [16], [17], [18]. The eutectic formed between the
Conclusions
Cast Mg92Y4Zn4 (composition in wt%) billet was subjected to severe plastic deformation by three different routes, namely ECAP, HPT and ECAP followed by HPT. The LPSO phases were shown to deform by bending and rearrangement within a soft magnesium matrix, where a substantial grain refinement down to 200–300 nm takes place. Further increases in plastic strain and the associated temperature rise appear to initiate dynamic recrystallisation and/or dynamic recovery of the magnesium matrix leading to
Acknowledgement
This project was supported by the U.S. Army International Technology Center – Pacific and the US Army Research Laboratory (FA5209-11-T-0043), under programme managers Dr. Christopher Drew and Dr. Vincent Hammond, respectively.
References (24)
- et al.
Acta Mater.
(2003) - et al.
Acta Mater.
(2000) - et al.
Mater. Sci. Eng. A
(2006) - et al.
Scr. Mater.
(2003) - et al.
Mater. Sci. Eng. A
(2010) - et al.
Mater. Sci. Eng. A
(2010) - et al.
Acta Mater.
(2010) - et al.
Mater. Sci. Eng. A
(2009) - et al.
Intermetallics
(2010) - et al.
Comput. Coupling Ph. Diagr. Thermochem.
(2006)
Acta Mater.
Intermetallics
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