Study On Impression Creep Behavior Of ZK60 Magnesium Alloy

The extruded ZK60 and ZK60+1%Y magnesium alloys were used as the research object,and the self-made device was used to carry out the pressure-in test.Then the steady-state creep constitutive equation was established to analyze the creep mechanism of the extruded ZK60 and ZK60+1%Y magnesium alloys under the experimental conditions.The organization evolution law of the extruded ZK60 and ZK60+1%Y magnesium alloys before and after creep were observed by XRD,SEM and EDS.The results are as follows:1)The behavior characteristics of the extruded ZK60 and ZK60+1%Y magnesium alloys were investigated under the condition of temperature of 100?225? and stress of 25?175MPa.The constitutive equation of creep stage is established by introducing stress exponent n and creep activation energy parameter Q:(a)The average value of stress exponent n of the extruded ZK60 magnesium alloy is 4.823 under the condition of temperature 100?150? and stress 100?175MPa,the average value of creep activation energy Q is 4.8 KJ/mol,the constant value of material structure A is 5.6,and the constitutive equation of the steady-state press-in creep is as follows:?= 5.6?4.823 exp(-41118/RT)(b)The average value of the stress exponent n of the extruded ZK60 magnesium alloy is 1.754 under the condition of temperature 175?225? and stress 25?100MPa,the average value of creep activation energy Q is 77.848KJ/mol,the constant value of the material structure A is 0.05,and the constitutive equation of the steady-state press-in creep is as follows:? = 5.0×10-2?1.754 exp(-77848/RT)(c)The average value of stress exponent n of the extruded ZK60+1%Y magnesium alloy is 3.214 under the condition of temperature 100?150? and stress 100?175MPa,the average value of creep activation energy Q is 50.148 KJ/mol,the constant value of material structure A is 2.08,and the constitutive equation of the steady-state press-in creep is as follows:?= 2.08?3.214 exp(-50148/RT)(d)The average value of stress exponent n of the extruded ZK60+1%Y magnesium alloy is 2.023 under the condition of temperature 175?225? and stress 25?100MPa,the average value of creep activation energy Q is 99.413 KJ/mol,the constant value of material structure A is 0.029,and the constitutive equation of the steady-state press-in creep is as follows:? = 2.9×10-2 ?2.023 exp(-99413/RT)2)Based on the constitutive equation of the steady-state press-in creep,the creep mechanism of the extruded ZK60 and ZK60+1%Y magnesium alloy are as follows under the temperature and stress conditions set by this experiment:(a)The creep mechanism of the extruded ZK60 magnesium alloy conductor is grain boundary sliding by dislocation climbing under the condition of low temperature and high pressure;The creep mechanism of the extruded ZK60 magnesium alloy conductor is grain boundary diffusion by grain boundary sliding under the high temperature and low pressure.(b)The creep mechanism of the extruded ZK60+1%Y magnesium alloy conductor is grain boundary sliding by dislocation slip under the condition of low temperature and high pressure;The creep mechanism of the extruded ZK60+1%Y magnesium alloy conductor is the self-mechanism of Mg by grain boundary slip under the high temperature and low pressure.3)The microstructure of the extruded ZK60 magnesium alloy is mainly Mg phase before creep,MgZn2 and MgZn phases precipitate after creep,and a small amount of Zr-Zn phase.Under the conditions of high temperature and low pressure,the intragranular precipitates are granular,relatively small,and evenly distributed on the matrix.Under the conditions of low temperature and high pressure,the grain size is large,which is band-shaped distribution and uneven distribution,and the creep resistance of the alloy will decrease.4)The microstructures of the extruded ZK60+1%Y magnesium alloy is composed of?-Mg matrix and ?-Mg3Zn3Y2 phase before creeping,after the press-in creep,in addition to MgZn2,MgZn,Y-Zn and Mg-Y rare earth phase precipitate.When the temperature is low,the precipitation is gray striped distribution in the matrix.When the temperature is high,the precipitation of rare earth phase increased and was discontinuous thin strip and fine granular uniform distribution in the matrix.The precipitation of rare earth compound phase of high thermal stability,which can improve the creep resistance of the alloy.5)During the creep experiment,in the region far from indenter and the region under the indenter which has an approximately hemispherical shape,no microstructural changes are detectable.The remaining region is deformation region.In the deformation region,the grain is gradually elongated along the deformation direction.