Effect Of Heat Treatment On Microstructure,high Temperature Creep And Mechanical Properties Of Mg-6Al Alloy With Compound Addition Of Nd And Gd

The article mainly explores the effects of the solution treatment(T4)and solution+aging treatment(T6)on the microstructure and high temperature creep and tensile properties of Mg-6Al alloys with Nd and Gd.Optical microscope(OM)and scanning electron microscope(SEM)are taken to observe the microstructure of different heat-treated states after high-temperature creep and high-temperature tensile;X-ray diffraction analysis(XRD)and energy spectrum analysis are taken to study the phase composition of the alloy;Transmission electron microscopy(TEM)studies the orientation relationship between the matrix and the second phase and the dislocation distribution.The age hardening behavior of Mg-6Al-1Nd-xGd(x=0,0.5,1,1.5wt%)alloy is investigatived;The Mg-6Al-1Nd-1Gd alloy in two heat treatment states of T4 and T6 are conduct to high temperature compression creep experiment under the conditions of 150?,175?,200? and 50MPa,70MPa,90MPa to analyze the influence of T4 and T6 heat treatment methods on the high temperature creep resistance of alloys;the Mg-6Al-1Nd-1Gd alloy in two heat treatment states of T4 and T6 are conduct to high temperature tensile experiment under the conditions of 150?,175?,200? to analyze the tensile strength and fracture morphology.Finally,room temperature and high temperature tensile properties of Mg-6Al-1Nd-xGd(x=0,0.5,1,1.5wt%)alloy with different Gd contents after T6 treatment are investigatived.The conclusions obtained are as follows:(1)The best parameter of the solution treatment in this experiment is 420?‘24h.At this parameter,the Vickers hardness of the Mg-6Al-1Nd-1Gd alloy reaches 32.24 HV5.After T6 treatment,due to the increase of Gd content,the volume fraction of intermetallic compounds Al2RE(Nd?Gd)in the Mg-6Al-1Nd-xGd(x=0,0.5,1,1.5wt%)alloy is increase which has a stronger effect on the ?-Mg17Al12 phase resulting in a greatly reduce of ?-Mg17Al12 phase.At the same time,the addition of Gd would prolong the aging process of the Mg-6Al-1Nd-xGd alloy.With the increase of Gd content,the hardness peak of the alloy when age at 200? is delayed from 28h to around 36h,and the peak value of the alloy when the Gd content is 1%The hardness is the largest,reaching 53.1 HV5.(2)Both T4 and T6 heat treatments could improve the high temperature creep resistance of the alloy.After T4 treatment,the alloy has the highest improvement in creep resistance.While 70MPa,200?,the creep strain and steady-state creep rate of the Mg-6Al-1Nd-1Gd alloy wtih T4 state reduce to 1.8%and 2.333×10-8 s-1,respectively.The creep resistance of the alloy is significantly affected by temperature.When the creep temperature increases from 150? to 200?,the creep strain and steady-state creep rate increase from 0.55%and 5.306×10-9 s-1 to 1.8%and 2.333×10-8s-1,respectively,improving the nearly an order of magnitude.(3)Through calculation and microstructure analysis,the creep mechanism of Mg-6Al-1Nd-1Gd alloy in different heat treatment states is obtained.The creep mechanism of Mg-6Al-1Nd-1Gd alloy in T4 and T6 states are both combined effect of dislocation slip and grain boundary slip.(4)Both T4 and T6 heat treatment can improve the high temperature mechanical properties of the alloy.At 200?,the tensile strength of the T6 Mg-6Al-1Nd-1Gd alloy reaches the maximum,and the elongation of the T4 alloy reaches the maximum.The influence of temperature on the alloy is obvious.The tensile strength decreases with the increase of temperature,and the elongation increases with the increase of temperature.When the temperature rises from 150? to 200?,the tensile strength of T6 state Mg-6Al-1Nd-1Gd alloy drop from 196.37MPa to 146.71MPa,droped 25.29%and the elongation increase from 8.42%to 22.3%.(5)With the increase of the Gd content,the room temperature and high temperature tensile properties of the T6 state Mg-6Al-1Nd-xGd(x=0,0.5,1,1.5wt%)alloy both increase first and then decrease.The tensile strength of Mg-6Al-1Nd-1Gd alloy at room temperature(20?)and high temperature(150?,175?,200?)is the best,which are 214.49MPa,196.37MPa,178.56MPa and 146.75MPa,respectively.