A Review on Developments in Magnesium Alloys

Abstract

In order to facilitate the understanding of the current research efforts and directions, this article first introduces the anomalous/problematic features of magnesium (Mg) and presents the recent approach of stacking fault energy (SFE)-based alloying element selection to lessen or eliminate this problem. Stacking fault energy computations via ab initio techniques necessitate an understanding of the free electron density distribution around atoms in a solid solution. Therefore, the assessment of the role of atoms by also considering the possibility of short range order (SRO) formation rather than a random solid solution has been revisited. Two possible types of SRO have been indicated. The relevant electronic interactions between the host Mg and the alloying element atoms are more clearly incorporated in a generally less known model by Miedema based on atomic-level thermodynamics rather than in Hume-Rothery rules. This more successful approach has also been addressed here. An evaluation founded on these premises, introducing the relatively more recent Mg alloy systems, has been given in terms of their achievements toward healing the problematic features of Mg alloys. The spectrum of alloy systems discussed ranges from doping of Mg to dilute alloy systems and to some rich alloy systems that offer remarkable properties. Among the first category, an unorthodox addition, doping with oxygen, and its implications, has been presented. The dilute alloy systems and their compositional design based on SRO and SFE together with their potentials have been reviewed. Among the rich alloy compositions, the most interesting precipitate systems, that is, the ones involving order and intermetallic formations, long-period stacking order phases, and quasi-crystals, have been discussed. Among all the alloying elements, one that deserves particular attention, calcium, with its implications such as being economical, offering environmentally friendly Mg metallurgy, and remedial effects on the shortcomings of engineering properties, and a closely related issue of calcium oxide (CaO) addition have been scrutinized. This article also makes an attempt to point out the future directions throughout the text, whenever possible.

Improving the corrosion behavior of magnesium alloys with a focus on AZ91 Mg alloy intended for biomedical application by microstructure modification and coating

“…Plastic deformation forms that usually activated in Mg and its alloys embrace intra-granular slip, twinning mode, and inter-granular grain boundaries sliding. 1 Figure 7 shows the slip and twinning systems in the hexagonal structure of Mg. 48 Depending on the amount of strain and the deformation temperature, the dynamic recrystallization can also cause the plastic deformation. The activity of the sliding systems in Mg gradually becomes more difficult to deform.…”

“…Solidification texture in metals with a hexagonal close-packed (HCP) structure, c/a ratio determines the solidification texture. Magnesium has a different 48 solidification texture. Pure as-cast Mg exhibits a [0001] direction perpendicular to the direction of columnar grain growth.…”

Assessing the long-term in vivo degradation behavior of magnesium alloys - a high resolution synchrotron radiation micro computed tomography study

“…Biodegradable magnesium (Mg)-based implants are of great interest in musculoskeletal research and application due to their ability to degrade in the body, thus requiring no secondary surgery for removal in situations where the implant is not meant to remain in the body permanently (1)(2)(3)(4). Apart from their degradability, the Young's modulus of Mg is similar to that of bone and hence causes less stress shielding compared to conventional implant materials such as titanium (Ti) and medical steel (5).…”

The Pilling-Bedworth Ratio of Oxides Formed From the Precipitated Phases in Magnesium Alloys

“…There are many precipitated phases existing in magnesium alloys, including Mg 17 Al 12 , MgZn 2 , Mg 2 Ca, Mg 5 Gd, Mg 12 Nd and Mg 24 Y 5 , etc., (Nie 2012;Zhu and Chen, 2019;Kaya, 2020;Shi et al, 2020). The crystallography of the precipitated phases determines the microstructure and property of magnesium alloys.…”