Creep Behavior Of Extruded AZ91 Magnesium Alloy

AZ91 magnesium alloy has been widely used in aerospace,transportation,electronics and other fields,due to its advantages of small density,high specific strength and so on.But some weakness such as poor mechanical properties above 120? restrict the application of AZ91.In order to study the mechanical properties above 120? of AZ91 magnesium alloy and factors which affect the mechanical properties of AZ91.Extruded AZ91 magnesium alloy as the main object has been studied by the homemade device at 150-200?,and the influence of the content of Al and the forming technology on the creep properties are anayzed.The major contests and conclusions are as follows:(1)The creep properties of extruded AZ91 magnesium alloy,extruded AZ61 magnesium alloy and cast AZ91 D magnesium alloy are studied under 150-200? ? 120-160 Mpa.The research results show that: The steady-state creep rate and total creep depth of the three alloys are increased with stress and temperature.And the steady-state creep rate and total creep depth depend on temperature more than stress.In the same conditions,the steady-state creep rate and total creep depth of extruded AZ91 magnesium alloy is the minimum of these three alloys.(2)Analysing the microstructure before and after creep of three alloys by XRD,SEM,EDS,the results show that: Before and after creep,these alloys consist of ?-Mg and?-Mg17Al12.In the extruded alloy,a small amount of ?-Mg17Al12 are distributed in grain boundaries.In the cast alloy the branch ?-Mg17Al12 is distributed in the magnesium substrate,which is more than that in the extruded alloy.During creep process,the content of ? phase increased with temperature and stress in the deformation region of these alloys.(3)Stress exponent and creep activation energy of three alloys are calculated by constitutive equation,and the creep mechanism are analyzed.The results show that: Under the experimental conditions,the stress exponent of AZ91,AZ61,AZ91 D are 5.1,5.6,4.7,the apparent creep activation energy are 111.2kJ/mol,122.2kJ/mol,94.2kJ/mol,the really creep activation energy are 115.7kJ/mol,127.1kJ/mol,98.5kJ/mol;The dominance creep mechanism of extruded AZ91 magnesium alloy is diffusion-contorlled dislocation climb.The dominance creep mechanism of extruded AZ61 magnesium alloy is lattice-diffusion-contorlled dislocation climb.The dominance creep mechanism of cast AZ91 D magnesium alloy is diffusion-contorlled dislocation climb.(4)Studing the influence of the content of Al and the forming technology on creep properties of AZ91 magnesium alloy,the results show that: the creep resistance of extrudedAZ91 magnesium alloy is better than that in extruded AZ61 magnesium alloy.In the cast AZ91 D magnesium alloy,the amount of ? phase is more than AZ91,and the creep resistance of cast AZ91 D magnesium alloy is worse than extruded AZ91 magnesium alloy.