Effects Of Zn Additions On Microstructure And Mechanical Properties Of Mg-Gd-Ca-Zr Alloy

Precipitation-hardenable Mg-Gd alloys have received extensive attention in aerospace and 3C fields due to their excellent mechanical properties and thermal stability.However,the high price of pure Gd metal limited the application of Mg-Gd alloys.Generally,Mg-Gd alloys containing less than 10 wt.%Gd have a poor age-hardening response at 200°C due to the low number densities of prismatic precipitate phases.Therefore,in this thesis,the effects of Zn additions on the mechanical properties of Mg-10Gd-0.6Ca-0.5Zr?wt.%?alloy were investigated,and the microstructure was characterized using scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,scanning transmission electron microscopy?STEM?and X-ray energy dispersive spectroscopy?EDS?.Meanwhile,the relationship between microstructure and mechanical properties was discussed.It is found that the as-quenched harness value and age-hardening response of Mg-10Gd-0.6Ca-0.5Zr alloy can be obviously improved with Zn additions.The as-quenched hardness value increased 9 HV with 1 wt.%Zn addition,which is attributed to the increased number density of undissolved Mg₅Gd particles,the formation of Zn₂Zr₃ phases and the grain refinement caused by Zn addition.The hardness increments of Mg-10Gd-0.6Ca-0.5Zr alloy from as-quenched condition to peak-aged condition aged at 200°C increased with 0.5 wt.%Zn addition?45 HV?,but reduced with 1 wt.%Zn addition?37 HV?.The precipitate phases in peak-aged Mg-10Gd-0.6Ca-0.5Zr alloy are?'phase and basal ternary phase containing Mg,Gd and Ca.With Zn additions,in addition to?'and basal ternary phase,?₁,?"and?'phases appeared.Zn segregation was detected in?₁ phase,thus the addition of Zn can promote the formation of?₁ phase.With 1 wt.%Zn addition,the number density of basal?"and?'phases increased,which cannot provide effective barrier to gliding dislocations and propagating twins in the magnesium matrix than the prismatic?'and?₁phases,therefore the hardness increment reduced.Lenticular shape?₁ phases with end facets connected to the basal ternary phases containing Mg,Gd and Ca other than?'phases were obsered in Zn-containing alloys.Some of them precipitate in the magnesium matrix,and others precipitate around Zn₂Zr₃ phases.