Trace Add Elements Sc, Mn Mg-gd Alloy

Magnesium alloys are attractive materials due to their low density,high specific strength,good electromagnetic shielding characteristics,and good machinability,etc.These favorable properties can contribute significantly to the aspect of weight savings in the design and construction of automobiles,mobile phones,aerospace components and computers.However,the extensive application of Mg alloys is limited due to their poor heat resistance and low mechanical properties at elevated temperature.It is therefore the objective to develop a promising alloy,based on the Mg-Gd alloy,with improved properties at elevated temperature.Optical microscope(OM),scanning electron microscope(SEM) equipped with energy spectrum analysis,transmission electron microscope(TEM),Gleeble-1500 thermal simulator,hardness testing and tensile testing were performed to investigate the structure effect of Zr,Mn and Mn+Sc on Mg-Gd alloy,to study the improved age-hardening effect on Mg-Gd alloy resulting from the addition of Mn and Sc,and to investigate the hot deformation behavior of Mg-Gd-Sc-Mn alloy with a physical simulation technique.Through the study,the following conclusions were obtained:1.The addition of Zr significantly refines the grains of as-cast Mg-Gd alloy by generating nucleants.However,prolongation of the holding time for homogenization treatment results in rapid grain coarsening.Also,Zr addition cannot restrict the growth of recrystallization grains during extrusion,and therefore completely loss the grain refining effect for Mg-Gd extruded alloy sample.The addition of Mn shows no grain refining effect for as-cast Mg-Gd alloy,but it can refine microstructure to some extent during extrusion.Successful grain refinement can be obtained by the addition of Mn+Sc.2.The optimized solution treatment regime of Mg-5.02Gd-0.71Sc-1.08Mn alloy has been established.That is the alloy is kept at 615℃for 24h..When the alloy was treated under 420℃～600℃,lots of small particles would precipitated,and during the thereafter aging treatment,the alloy showed no age-hardening effect.When the alloy was treated under 615℃for 24h,and aged at 200℃,250℃,300℃and 350℃,the alloy peak-value hardness were significantly increased 65.1%,47.6%,33.3%and 23.81%,respectively.3.When the deformation temperature is 300℃～500℃and the strain rate is 0.001～1s-1,the true stress-strain curve of Mg-10.2Gd-0.8Sc-1.7Mn alloy is the dynamic recrystallization type.The maximum value of flow stress increases with increase of strain rate or decreases with the deformation temperature.The activation energy for the experimental alloy changed unconspicuously when deformed under 350℃～450℃, however,significantly increased under 450℃～500℃.4.The Mg-10.2Gd-0.8Sc-1.7Mn alloy took place dynamic recrystallization during thermal deformation.The deformation temperature and strain degree had evident effects on the recrystallized microstructure and 400℃～450℃was rational thermal deformation temperature range for the alloy.After hot extrusion at 420℃and T5 treatment,the alloy ultimate strength and elongation percentage tested under 300℃were 275MPa and 40%,respectively.