Synergetic Effect of Grain Refinement and Spherical Shaped Precipitate Dispersions in Fracture Toughness of a Mg-Zn-Zr Alloy

Abstract

Fracture toughness was examined on a commercial Mg-Zn-Zr alloy, ZK60. The commercial alloy was extruded at a temperature of 493 K to obtain fine grain structures having fine spherical shaped precipitates. The microstructures consisted of equi-axed grains. The average grain size and the precipitate diameter were about 3 mm and 25 $ 50 nm, respectively. The yield strength and elongation-to-failure were 287 MPa and 26.7%, respectively. The plane-strain fracture toughness, K IC , was estimated to be 34.8 MPam 1=2 by the stretched zone analysis. These mechanical properties were superior to that of conventional wrought magnesium and magnesium alloys. The deformed microstructure observations showed i) the activation of non-basal dislocations even at room temperature and ii) the pinning of dislocations by the spherical shaped precipitates during the fracture toughness test. Thus, a combination of grain refinement and dispersion of fine spherical shaped precipitates were found to be effective methods for improving the fracture toughness of magnesium alloys.

Effect of Initial Grain Size on Dynamically Recrystallized Grain Size in AZ31 Magnesium Alloy

“…1) Die casting and injection molding are the main method of manufacturing such components, 2) however, plastic forming technologies such as hot drawing and hot forging with high productivity have been developed to form thinner walls of the components without defects. 3,4) In the drawing process, it has been clearly demonstrated that the critical strain rate increase with the refinement of grain size in AZ31 magnesium alloy at 523 K. 5) Thus, grain size refinement of magnesium alloys is essential not only for the development of superior mechanical properties at room temperature such as higher strength, toughness 6,7) and ductility, 8) but also for the higher productivity. In general, dynamic restoration behavior is dependent on the stacking fault energy (SFE) and lattice diffusivity.…”

Correlation between microstructure and tensile behavior in powder metallurgy ZK60 alloys

“…Hence, the selection of a suitable alloying element or secondary particles into the PM Mg alloy is also essential. Considering that the extruded ZK60 alloy containing hard MgZn 2 phase particles usually exhibit good ductility ( 415%) [7], fabricating an ultrahigh-strength and high-ductility ZK60 alloy via PM processing is possible. Besides, the correlation between the microstructure and tensile behavior in the PM ZK60 alloy was discussed briefly.…”

High Strength and Fracture Toughness Balances in Extruded Mg-Zn-RE Alloys by Dispersion of Quasicrystalline Phase Particles

“…34) The dislocation movement is easily interrupted, as does a conventional second-phase particle, regardless of the interface structures. In the fracture toughness test, recent studies have also shown that the quasicrystalline phase particle 20) and the precipitate particle 7) have a role of pinning the dislocation movements. However, the interface structures affect the nucleation site for void formation when the strains are increased: the fracture occurs at the interface between the matrix and the particle or in the particle itself, for the particle consisting of an incoherent interface.…”

“…5,6) In addition, the dispersion of fine spherical shaped precipitates enhances the fracture toughness by pinning the dislocation movements around them. 7,8) Controlling the grain refinement and/or the presence of precipitates in the matrix are clearly effective methods for improving the fracture toughness in magnesium and magnesium alloys.…”