Enhancing plastic deformability of Mg and its alloys—A review of traditional and nascent developments

Mg and its alloys have continued to attract interest for several structural and super-sensitive applications because of their light weight and good combination of engineering properties.However for some of these applications,high plastic deformability is required to achieve desired component shapes and configurations;unfortunately,Mg and its alloys have low formability.Scientifically,the plastic behaviour of Mg and its alloys ranks among the most complex and difficult to reconcile in metallic material systems.But basically,the HCP crystal structure coupled with low stacking fault energies(SFE)are largely linked to the poor ductility exhibited by Mg alloys.These innate material characteristics have regrettably limited wide spread applicability of Mg and its alloys.Several research efforts aimed at exploring processing strategies to make these alloys more amenable for high formability–mediated engineering use have been reported and still ongoing.This paper reviews the structural metallurgy of Mg alloys and its influence on mechanical behaviour,specifically,plasticity characteristics.It also concisely presents various processing routes(Alloying,Traditional Forming and Severe Plastic Deformation(SPD))which have been explored to enhance plastic deformability in Mg and its alloys.Grain refinement and homogenising of phases,reducing CRSS between slip modes,twinning suppression to activate non-basal slip,and weakening and randomisation of the basal texture were observed as the formability enhancing strategies explored in the reviewed processes.While identifying the limitations of these strategies,further areas to be explored for enhancing plasticity of Mg alloys are highlighted.

Textural Evolution of AZ31B Magnesium Alloy Sheets Undergoing Repeated Unidirectional Bending at Room Temperature

In this paper, repeated unidirectional bending （RUB）, was applied to improve the texture of AZ31B magnesium alloy sheets so as to enhance their stamping properties. The samples undergoing RUB were annealed at different temperatures. The mechanical properties, formability, textural components and microstructure of the samples before and after RUB were characterized and compared. It was found that the basal textural component was reduced dramatically by RUB, and that （1212） and （1211） textural components appeared. Annealing has a great effect on the mechanical properties of samples undergoing RUB. The plasticity and stamping formability of samples were greatly improved by RUB and annealing at 260℃ for 1 h, and elongation to fracture and Erichsen value were increased to 38% and 67%, respectively.

An investigation on the hardness and corrosion behavior of MWCNT/Mg composites and grain refined Mg

In the present work,multi walled carbon nanotubes(MWCNT)reinforced magnesium(Mg)matrix composite was fabricated by friction stir processing(FSP)with an aim to explore its mechanical and electrochemical behavior.Microstructural observations showed that the thickness of the produced composite layer was in the range of 2500μm.FSP resulted uniform distribution of CNT near the surface while agglomerated layers in the subsurface.Grain refinement of Mg achieved by FSP improved the hardness but significant enhancement in the hardness value was observed for FSPed MWCNT/Mg composites.Potentiodynamic polarization studies revealed that the increase in corrosion current density was observed for MWCNT/Mg composite compared with grain refined Mg and pure Mg,implying the significance of secondary phase(MWCNT)in decreasing the corrosion resistance of the composite.

Microstructural characteristics and mechanical properties of the hot extruded Mg-Zn-Y-Nd alloys

A new type of Mg-Zn-Y-Nd alloy for degradable orthopedic implants was developed.In the present study,the Zn and Y content was adjusted and their influences on the microstructures and mechanical behaviors were discussed in depth.The results showed that the as-extruded Mg-Zn-Y-Nd alloys are mainly composed of fine dynamic recrystallized grains(DRXed grains),la rge unDRXed grains and linearly distributed secondary phases.The cha nge of Zn content exerts little influence on the grain structure of the extruded Mg-Zn-Y-Nd alloy,while the increase of Y content would hinder the dynamic recrystallization process and the growth of the DRXed grains,thus the size and volume fraction of the equiaxed DRXed grains decrease.The tensile and compressive properties are very little affected by Zn content because of the similar grain structure.As Y content increases,the tensile yield strength(TYS) and ultimate strength(TUS) increase while the elongation decreases,this is caused by a combined strengthening effect of grain refinement,texture,precipitation and twinning.The compressive yield strength(CYS) and ultimate strength(CUS) of Mg-Zn-Y-Nd alloy with diffe rent Y content exhibit a similar tendency as the tensile test.