Microforming is a promising approach to micromanufacturing miniaturized components. The material flow and tribological aspects of microforming are affected by the size effect. The size effect phenomenon is influenced by parameters such as the initial microstructure, deformation temperature, lubricant type, and billet geometry. The scope of this study is to establish tribology-based scientific knowledge by considering all the mentioned parameters. As a case study to mimic the tribological interaction during microforming, a micro double cup extrusion (MDCE) test is performed on engineered Magnesium QE22 materials. The experiments were performed on various grain sizes, lubricants, and temperatures. A comprehensive investigation of all the conditions indicated that the ultrafine-grained (UFG) microstructure is the best-suited initial microstructural condition for maintaining excellent surface morphology, surface roughness, and microstructural homogeneity. The coarse grain (CG) microstructure exhibited substandard surface properties and microstructural heterogeneity. Electron backscatter diffraction (EBSD) microstructural analysis revealed tribological interactions with the activated micromechanisms under coarse-grained (CG), fine-grained (FG), and ultrafine-grained (UFG) conditions. Under CG conditions, the activation of twins induced dynamic recrystallization resulting in a greater cup height ratio and coefficient of friction (COF). This shows the incompetence of the CG microstructure in accommodating friction-induced shear. On the other hand, the UFG microstructure demonstrated a resilient microstructure that easily accommodated the induced frictional shear by activating the grain boundary sliding (GBS) mechanism. The activation of the GBS mechanism resulted in complete anhelation of the frictional subsurface layer, thereby eliminating the tribological size effect that remained unaffected even when the billets were downsized.

Realising the potential of Magnesium (Mg), several globally leading ventures have invested in the Mg industry, but their relatively poor corrosion resistance is a never ending saga till date. The corrosion and bio-corrosion behaviour of Mg has gained research attention and still remains a hot topic in the application of automobile, aerospace and biomedical industries. The intrinsic high electrochemical nature of Mg limits their utilization in diverse application. This scenario has prompted the development of Mg composites with an aim to achieve superior corrosion and bio-corrosion resistance. The present review enlightens the influence of grain size (GS), secondary phase, texture, type of matrix and reinforcement on the corrosion and bio-corrosion behaviour of Mg composites. Firstly, the corrosion and bio-corrosion behaviour of Mg composites manufactured by primary and secondary processing routes are elucidated. Secondly, the comprehensive corrosion and bio-corrosion mechanisms of these Mg composites are proposed. Thirdly, the individual role of GS, texture and corrosive medium on corrosion and bio-corrosion behaviour of Mg composites are clarified and revealed. The challenges encountered, unanswered issues in this field are explained in detail and accordingly the scope for future research is framed. The review is presented from basic concrete background to advanced corrosion mechanisms with an aim of creating interest among the readers like students, researchers and industry experts from various research backgrounds. Indeed, the corrosion and bio-corrosion behaviour of Mg composites are critically reviewed for the first time to: (ⅰ) contribute to the body of knowledge, (ⅱ) foster research and development, (ⅲ) make breakthrough, and (ⅳ) create life changing innovations in the field of Mg composite corrosion.

Mg-4Zn-1RE-0.5Zr (ZE41) Mg alloy is extensively used in the aerospace and automobile industries. In order to improve the applicability and performance, this alloy was engineered with in-situ TiB₂ reinforcement to form TiB₂/ZE41 composite. The high temperature deformation behavior and manufacturability of the newly developed TiB₂/ZE41 composite and the parent ZE41 Mg alloy were studied via establishing constitutive modeling of flow stress, deformation activation energy and processing map over a temperature range of 250 ℃ - 450 ℃ and strain rate range of 0.001 s⁻¹ - 10 s⁻¹. The predicted flow stress behavior of both materials were found to be well consistent with the experimental values. A significant improvement in activation energy was found in TiB₂/ZE41 composite (171.54 kJ/mol) as compared to the ZE41 alloy (148.15 kJ/mol) due to the dispersed strengthening of in-situ TiB₂ particles. The processing maps were developed via dynamic material modeling. A wider workability domain and higher peak efficiency (45%) were observed in TiB₂/ZE41 composite as compared to ZE41 alloy (41%). The Dynamic recrystallization is found to be the dominating deformation mechanism for both materials; however, particle stimulated nucleation was found to be an additional mode of deformation in TiB₂/ZE41 composite. The twinning and stress induced cracks were observed in both the materials at low temperature and high strain rate. A narrow range of instability zone is found in the present TiB₂/ZE41 composite among the existing published literature on Mg based composites. The detailed microstructural characterization was carried out in both workability and instability domains to establish the governing deformation mechanisms.

Existence of tension – compression yield asymmetry is a serious limitation to the load bearing capablities of Magnesium alloys in a number of light weight structural applications. The present work is aimed at nullifying the tension to compression asymmetry problem and strain hardening anomalies in a Magnesium – Silver – Rare Earth alloy by engineering different levels of microstructural conditions via friction stir processing and post process annealing. The existence and extent of yield asymmetry ratio in the range of microstructural conditions was experimentally obtained through quasistatic tensile and compression tests. The yield asymmetry problem was profoundly present in specimens of coarse grained microstructures when compared to their fine grained and ultra fine grained counterparts. The impact of the microstructure and associated mechanisms of plasticity on the macroscopic strain hardening behavior was established by Kock – Mecking’s analysis. Crystal plasticity simulations using Viscoplastic Self Consistency approach revealed the consequential role of extension twinning mechanism for the existence of yield asymmetry and anomalies in strain hardening behavior. This was especially dominant with coarsening of grain size. Electron Microscopy and characterization were conducted thoroughly in partially deformed specimens to confirm the predictions of the above simulations. The role of crystallographic texture for inducing the polarity to Tension – Compression yield asymmetry was corroborated. A critical grain size in Magnesium – Silver – Rare earth alloy was hereby established which could nullify influences of extension twinning in yield asymmetry ratio.