The Study On Correlation Between Solute Drag And Mechanical Properties In High Temperature Deformation Of Magnesium Alloys

Mg alloys have great application prospects in aerospace and rail transit,but their poor high-temperature performances and creep resistance restrict their wide application.The problem about promoting high-temperature performances of Mg alloy has always been significant but difficult.Mg-RE alloys are the Mg alloys with the best heat resistance,as reported so far.Researching on high-temperature properties and creep resistance of Mg-RE alloys are mainly focused on strengthening effects of precipitation,but few of them are on the interaction between solute atoms and dislocations and grain boundaries.Studying drag effect of solute atoms on dislocations during high-temperature tensile and creep deformation of Mg-RE alloys,and discussing effects of solute drag on high-temperature performance and creep resistance,can provide theoretical guidance for the development of heat-resistant Mg alloys with high strength.In this paper,using Mg-2wt.%Gd,Mg-0.5wt.%Ce,Mg-5Gd-3Y(GW53,wt.%)and Mg-8Gd-3Y(GW83,wt.%)as research objectives,the solute drag effect during high-temperature tensile deformation and the effect of solute drag on high-temperature mechanical properties and creep resistance of binary Mg alloys and Mg alloys with different Gd concentration were investigated by electron backscatter diffraction analysis(EBSD),high-angle annular dark-field scanning transmission electron microscope(HAADF-STEM),high temperature tensile test and tensile creep test.The results are presented as follow:1)In the binary alloy system,tensile and yield strengths of Mg-2wt.%Gd were significantly better than those of Mg-0.5wt.%Ce.Its tensile and yield strengths at 200?were 107 MPa and 90 MPa,respectively,which were 53%and 35%higher than those of Mg-0.5wt.%Ce.At 200?and under the same stress,the minimum creep rate of Mg-2wt.%Gd was three orders of magnitude lower than that of Mg-0.5wt.%Ce,and its creep resistance was significantly better than that of Mg-0.5 wt.%Ce.The creep stress indexes of the two alloys were 3.3 and 4.3,indicating that their main creep mechanisms were dislocation creep mode.2)The tensile curves of Mg-2wt.%Gd at 150?and 200?showed serrated yield,while Mg-0.5wt.%Ce did not appear,which was a typical dynamic strain aging(DSA)effect caused by the interactions between RE solute atoms and dislocations.The stronger drag effect of solute in Mg-2wt.%Gd made its high temperature mechanical properties and creep resistance better than those of Mg-0.5wt.%Ce.3)Comparing the Mg alloys with different Gd concentrations,the high-temperature strength of Mg alloys improved with the increase of Gd concentration.At 100-400?,the tensile and yield strength of GW83 alloy were significantly better than those of GW53 alloy and Mg-2wt.%Gd.Its tensile and yield strengths at 200?were 235 MPa and 179 MPa,respectively,which were 25%and 36%higher than those of GW53 alloy,and 120%and 101%higher than Mg-2wt.%Gd.At 200?and under the same stress,the minimum creep rate of GW83 alloy was four orders of magnitude lower than that of Mg-2wt.%Gd and one order of magnitudes lower than that of GW53.4)DSA effects had been showed during tensile tests at 100?-350?in GW83,100?-300?in GW53 and 150?-200?in Mg-2wt.%Gd.The temperature range of DSA effect in GW83 was the widest,and that in Mg-2wt.%Gd was the narrowest.This was mainly because the concentration of RE solute atoms in GW83 was the largest,and the interaction between solute atoms and dislocations was stronger.5)Compared with the creep dominated by dislocation slip in binary Mg alloys,a large number(sum)of?'phase(Mg₇Gd)precipitated in GW83during the creep process.Its structure is orthogonal and its relationship with matrix is(100)?//(12?10).The large amount of?'phase precipitating in GW83 alloys would occupy vacancies in the solid solution,reduce the vacancy ratio,hinder dislocation climbing and improve its creep resistance.