Influence of Zn Content on Microstructure and Tensile Properties of Mg–Zn–Y–Nd Alloy

In the present study,the effect of Zn content on the microstructure and deformation behavior of the as-cast Mg-Zn-Y-Nd alloy has been investigated.The results showed that as Zn content increased,the volume fraction of secondary phases increased.Moreover,the phase transformation from W-phase to W-phase and I-phase occurred.In the as-cast state,W-phase exists as eutectic and large block form.When Zn content increases to 6 and 8%（wt%）,small I-phase could precipitate around W-phase particles.Additionally,the effect of Zn content on the tensile properties and deformation behavior varies with the testing temperature.At room temperature,the tensile strength increases with Zn content,whereas the elongation increases initially and then decreases.At 250℃,as Zn content increases,the tensile strength decreases initially and then increases slightly,whereas the elongation decreases.At 350℃,the elongation increases with Zn content,whereas the tensile strength decreases initially and then increases slightly.

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.

Tensile, creep behavior and microstructure evolution of an as-cast Ni-based K417G polycrystalline superalloy

The Ni-based K417G superalloy is extensively applied as aeroengine components for its low cost and good mid-temperature （600-900 ~C） properties. Since used in as-cast state, the comprehensive under-standing on its mechanical properties and microstructure evolution is necessary. In the present research, the tensile, creep behavior and microstructure evolution of the as-cast K417G superalloy under differ-ent conditions were investigated. The results exhibit that tensile cracks tend to initiate at MC carbide and γ＇/γ＇ eutectic structure and then propagate along grain boundary. As the temperature for tensile tests increases from 21 ℃ to 700 ℃, the yield strength and ultimate tensile strength of K417G superalloy decreases slightly, while the elongation to failure decreases greatly because of the intermediate tem- perature embrittlement. When the temperature rises to 900 ℃, the yield strength and ultimate tensile strength would decrease significantly. The creep deformation mechanism varies under different test-ing conditions. At 760 ℃/645 MPa, the creep cracks initiate at MC carbides and γ/γ＇ eutectic structures, and propagate transgranularly. While at 900℃/315 MPa and 950℃/235 MPa, the creep cracks initiate at grain boundary and propagate intergranularly. As the creep condition changes from 760 ℃/645 MPa to 900 ℃/315 MPa and 950 ℃/235 MPa, the γ＇ phase starts to raft, which reduces the creep deformation resistance and increases the steady-state deformation rate.

Effect of extrusion process on the mechanical and in vitro degradation performance of a biomedical Mg-Zn-Y-Nd alloy

A new type of biomedical Mg-Zn-Y-Nd alloy was developed and thermal extruded by different processes to investigate the effect of extrusion ratio and extrusion pass on its microstructure,mechanical property and degradation performance.The results show that the increase of extrusion ratio could promote the dynamic recrystallization(DRX)process and led to the coarsening of DRXed grains.While the increase of extrusion pass also contributes to the DRX process but refines the DRXed grains.The simultaneous increasing of extrusion ratio and extrusion pass refines the secondary phases obviously.The increase of extrusion ratio has reduced the tensile strength but improved the elongation of the alloy significantly.However,the increase of extrusion pass could enhance the tensile strength and elongation simultaneously,especially the strength.The degradation performance has been optimized effectively through increasing the extrusion ratio and extrusion pass.