**Abstract**

High Entropy alloys (HEAs) or Complex Concentrated Alloys (CCAs) or Multi-Principal Element Alloys (MPEAs) is a matter of interest to material scientists for the last two decades due to the excellent mechanical properties, oxidation and corrosion resistant behaviors. One of the major drawbacks of HEAs is their high density. Mg containing HEAs show low density compared to peers, although extensive research is required in this field. This chapter aims to include all the available information on synthesis, design, microstructures and mechanical properties of Mg containing HEAs and to highlight the contemporary voids that are to be filled in near future.

**Keywords:** Magnesium, High Entropy Alloys, Light Weight Alloys, Microstructure, Mechanical Properties

## **1. Introduction**

The ancient strategy of alloy design and production has been followed for a long period and it will remain a crucial part of industry. The strategy is based on one principal element solvent with solute elements dissolved in the lattice either as heterogeneities or precipitate particles. Although, ancient Indian scriptures in Sanskrit mentions the existence of multi principal alloys named as "Tri-loh" (loh means Iron), "Panch-dhatu" and "Asht-dhatu" in which Tri, Panch and Asht mean three, five and eight respectively [1]. These dhatus or metals were used for special and sacred purposes such as making idols, deities and machines [2]. The context of these alloys can be found in books and Sanskrit text titled "Vimanika Shastra", "Ras-Ratnakar-Samuchaya", "Shilparatna", "Manasara", "Ras-Tarangini", and "Ras-grandhas". These alloys were used for special purposes and the knowledge of their synthesis was mostly limited to the *Sages* and *Rishis*, which has never been researched and explored by the scientific community. The concept of multi principal element or high entropy alloy is modern version of the "Panch-dhatu".

The concept of maximization of configurational entropy by using five or more elements in nearly equi-atomic composition has revolutionized the field of alloy design and metallurgy. The first scientific report of such alloys were reported independently by Cantor et. al. and Yeh et. al [3, 4]. HEAs show better mechanical, oxidation, corrosion and irradiation properties compared to commercial alloys. HEAs show four key effects and a postulate, which are: high-entropy effect, severe lattice distortion, sluggish diffusion, short range order effect and cocktail effect [5].
