| Magnesium alloy is commonly used in commercial magnesium alloy,magnesium alloy due to the precipitation of low melting point Mg17Al12,the high temperature performance is poor,so in the automotive and aerospace power components(service temperature is generally higher at 150? and above)On the application of less.Therefore,more and more attention has been paid to the study of Mg-Zn magnesium alloys in which Zn is partially or completely substituted for Al.However,the increase of Zn content will lead to hot cracking tendency and micro-looseness of ingot,which is not conducive to the commercial casting production and processing of deformation,which greatly limits its application in industry.So we need to consider adding the third component to overcome this problem.The addition of rare earth elements can effectively improve the casting properties of Mg-Zn alloys.The addition of rare earth Ce in magnesium alloys is one of the directions to be studied.In addition to improving the casting properties,Ce and Mg can form high melting point compounds,can significantly improve the room temperature,high temperature mechanical properties and casting properties of magnesium alloys.According to the characteristics of Mg-Zn alloy with high strength and relatively poor casting performance,by adding Ce element,the defect can be improved and the magnesium alloy with good performance can be obtained.Moreover,addition of Ce in the magnesium alloy can weaken the texture during plastic deformation and obtain good plasticity.In this paper,Mg-Zn-Ce magnesium alloys with different magnesium rich angles were prepared:Mg-x(x=0.5,2.0,4.0,6.0)Zn-2.0Ce and Mg-x(x=0.5,2.0,4.0,6.0)Zn-0.2Ce alloy.The microstructures of as-cast,heat-treated and multi-pass hot-rolled alloys were investigated by means of optical microscope and scanning electron microscope;through the analysis of scanning electron microscope(EDS),X ray diffraction(XRD)analysis of hot-rolled alloy phase composition;by transmission electron microscopy(TEM)analysis precipitation aging phase and morphology of heat treatment Mg-6.0Zn-0.2Ce alloy at 450?×10h solid solution+190?×(4,8h)aging treatment;micro-hardness testing of cast and heat treatment state and multipass hot-rolled alloy with hardness tester,test the mechanical properties of hot-rolled alloy by tensile test machine,for alloy under different treatment conditions,analysis of the influence of the content of Zn and Ce on the mechanical properties.According to the above experimental data,a comprehensive analysis,the following findings:(1)To study on cast magnesium alloy,the Ce content is the same,with the increase of Zn content,the grain refinement of primary phase precipitation increased;and with the increase of Zn content the hardness of the alloy increased,the content of Ce is 0.2wt.%the hardness of the alloy increases faster,this is due to the combined effect of grain refinement and precipitation phase distribution of diffuse results.When the content of Ce is 2.0wt.%,the content of primary phase is more than in grain boundary.(2)The heat treatment of magnesium alloy found that 450?×10h is the best solution treatment system.The aging treatment of Mg-6.0Zn-0.2Ce alloy at 450 ?×10h for different time(1?100h)at 190 ? showed that the aging effect of Mg-6.0Zn-0.2Ce alloy was more obvious and the hardness increased with the aging time,and reached the maximum value,then decreased slowly.The aging treatment was the best at 190?×8h,and the peak aging strength was 93.27HV.Transmission analysis of Mg-6.0Zn-0.2Ce alloy aging 4h and 8h samples,It is found that the two phases of the alloy have two kinds of second phase precipitation,the rod-shaped ?'1 phase and the discoid ?'2 phase.However,due to the precipitation size of the second phase of 4h aging is less than 8h precipitation size,and 4h disc precipitation phase of the ?'2 phase is little,has not achieved the best strengthening effect.The phase content and phase size of the second phase of 8h aging precipitation achieve the best aging strengthening effect.This shows that the second phase precipitation and the second phase morphology are the important factors of strengthening effect.(3)The hot rolled magnesium alloy has been found that after the hot-rolling at 400 ?,the dynamic recrystallization of coarse cast grain during hot-rolling deformation.After hot-rolling alloy precipitation were broken,uniformly distributed in the crystal.The dynamic recrystallization degree of Mg-6.0Zn-2.0Ce and Mg-2.0Zn-0.2Ce alloy is better.Compared with the as-cast alloys,the grain size of Mg-6.0Zn-2.0Ce hot-rolled grain was refined from 72?m to 12?m,the grain size of Mg-2.0Zn-0.2Ce was refined from 207.43?m to 11?m,and two organizations are to achieve different levels of refinement.The precipitated phases of Mg-0.5Zn-2.0Ce and Mg-0.5Zn-0.2Ce alloys are ?-Mg and Mg12Ce,the precipitated phases of Mg-x(x=2.0,4.0,6.0)Zn-2.0Ce and Mg-x(x=2.0,4.0,6.0)-0.2Ce is ?-Mg and T-phase.Tensile test showed that Mg-Zn-Ce in the alloy system,Mg-2.0Zn-0.2Ce alloy yield strength and tensile strength were 283MPa and 331MPa,and has a good plasticity elongation rate was 16.6%,comprehensive mechanical properties is best,this is due to the recrystallization of the alloy is more complete,grain tends to equiaxed,grain size is small,and dispersed distribution of precipitated phase. |
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