Abstract
Cast Mg–1Zn–1Ca alloy (ZX11) has been tested to evaluate its compressive strength between 25 °C and 250 °C, and workability in the range of 260–500 °C. The ultimate compressive strength of this alloy is about 30% higher than that of creep-resistant alloy Mg–3Sn–2Ca (TX32) between 25 °C and 200 °C, and exhibits a plateau between 100 °C and 175 °C, similar to TX32. This is attributed to Mg2Ca particles present at grain boundaries that reduce their sliding. The processing map, developed between 260 and 420 °C in the strain rate limits of 0.0003 s−1 to 1 s−1, exhibited two domains in the ranges: (1) 280–330 °C and 0.0003–0.01 s−1 and (2) 330–400 °C and 0.0003–0.1 s−1. In these domains, dynamic recrystallization occurs, with basal slip dominating in the first domain and prismatic slip in the second, while the recovery mechanism being climb of edge dislocations in both. The activation energy estimated using standard kinetic rate equation is 191 kJ/mol, which is higher than the value for lattice self-diffusion in magnesium indicating that a large back stress is created by the presence of Ca2Mg6Zn3 intermetallic particles in the matrix. It is recommended that the alloy be best processed at 380 °C and 0.1 s−1 at which prismatic slip is favored due to Zn addition. At higher strain rates, the alloy exhibits flow instability and adiabatic shear band formation at <340 °C while flow localization and cracking at grain boundaries occurs at temperatures >400 °C.
Highlights
Owing to their biocompatibility and non-toxic nature, zinc and calcium are promising alloying elements to develop Mg alloys for orthopedic implants and other medical applications
The microstructure, higher-temperature compressive strength, creep, and corrosion properties of as-cast ZX11 alloy have been evaluated recently [8] which showed that this alloy composition has a promise for the intended applications
The optical and SEM micrographs of ZX11 alloy in the initial cast condition are shown in Figure 1a,b respectively
Summary
Owing to their biocompatibility and non-toxic nature, zinc and calcium are promising alloying elements to develop Mg alloys for orthopedic implants and other medical applications. With a view to produce low cost Mg–Zn–Ca alloys, the amount of alloying additions were kept at minimum levels while developing Mg–1Zn–1Ca alloy that contains only 1 wt % of Zn and 1 wt % of Ca. The microstructure, higher-temperature compressive strength, creep, and corrosion properties of as-cast ZX11 alloy have been evaluated recently [8] which showed that this alloy composition has a promise for the intended applications. When Ca is added to Mg–Zn. Metals 2017, 7, 405 alloys, a thermally stable intermetallic phase Ca2 Mg6 Zn3 forms that increases the higher temperature strength of the alloy [8]. The higher temperature strength is lower in ECAP material compared with extruded alloy due to grain boundary sliding and grain boundary diffusion. Another objective has been to validate the developed technology by conducting forging experiments to produce a web-rib (cup) shaped component
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