| Mg-RE has become a popular research direction of magnesium alloys due to its excellent comprehensive properties.However,magnesium alloy castings obtained by ordinary smelting process have coarse dendrites and uneven distribution of rare earth alloys,resulting in unstable alloy properties,which greatly limits the application of rare earth magnesium alloys.Studies have shown that melt ultrasonic treatment can effectively refine the alloy structure and improve the mechanical properties of the alloy.Therefore,this article will use ultrasonic treatment of Mg-12Gd-0.5Zr alloy to study the effect of different ultrasonic power on Mg-12Gd-0.5Zr alloy and optimize the alloy ultrasonic treatment process.On this basis,in order to further improve the performance of Mg-12Gd-0.5Zr alloy,optimized ultrasonic treatment technology was used to study the structure and mechanical properties of Mg-12Gd-xY-0.5Zr alloy.This article takes Mg-12Gd-xY-0.5Zr(x=0,1,3,5 wt.%)alloy as the main object,smelted in the MF-2Kg intermediate frequency induction furnace,when the melt temperature is 730℃,the Mg-The 12Gd-xY-0.5Zr alloy melt is cast after ultrasonic treatment with powers of 0 W,700 W,1000 W,1500 W,and 2000 W for 60 s.Then solid solution at 520℃ for 0-12 h,and aging at 175 ℃～225 ℃ for 0-100 h to obtain samples of different treatment processes.Optical microscope(OM)and scanning electron microscope(SEM)were used to analyze the microstructure morphology;transmission electron microscope(TEM),X-ray diffraction(XRD),and differential thermal analyzer(DSC)were used for phase analysis;Brinell hardness Machine and electronic universal testing machine for mechanical performance test.To study the effect of ultrasonic treatment and Y content on the as-cast,solid solution and aging treatment of Mg-12Gd-0.5Zr alloy.The main conclusions are as follows:(1)Ultrasonic treatment can refine the microstructure of Mg-12Gd-0.5Zr alloy.After ultrasonic treatment,the as-cast Mg-12Gd-0.5Zr alloy structure gradually changes from coarse and uneven α-Mg to fine and uniform Equiaxed crystals,while increasing the volμme fraction of the second phase.With the increase of ultrasonic power,the α(Mg)equiaxed crystal size of the as-cast Mg-12Gd-0.5Zr alloy decreases first and then increases,and the volμme fraction of the second phase increases first and then decreases.When the ultrasonic power is 1500 W,the as-cast α(Mg)equiaxed crystal size of the Mg-12Gd-0.5Zr alloy is reduced from 50.5 μm(without ultrasonic)to 28.4 μm,a reduction of 43.7%;the volμme fraction of the second phase is reduced from 4.8%(Without ultrasound)to 6.7%(area ratio),an increase of 37.6%.(2)According to the as-cast Mg-12Gd-0.5Zr alloy mechanical properties change curve,with the increase of ultrasonic power,the Brinell hardness and tensile properties of Mg-12Gd-0.5Zr alloy show a trend of first increasing and then decreasing,Reaching the peak value at 1500 W.The hardness increased from 75.6 HBW to 77.1 HBW by 1.9%;the tensile strength increased from 140 MPa to 220.5 MPa.The increase was 62.5%,and the elongation increased by 500%.(3)When Y element is added to Mg-12Gd-0.5Zr alloy,Y will react with Mg to form Mg24Y5 phase.The microstructure of the alloy is composed of α-Mg,Mg5Gd and Mg24Y5 phases.As the Y content in the Mg-12Gd-0.5Zr alloy increases,the second phase in the alloy gradually rises and is distributed around the grains in a network.The mechanical properties of the Mg-12Gd-xY-0.5Zr alloy are also proportional to the Y content.Proportional.The volμme fraction of the second phase in Mg-12Gd-5Y-0.5Zr alloy is 6.9%,which has increased by 34.7%;the Brinell hardness of the alloy is 83.4 HBW,which is increased by 9.5%,the tensile strength is 275 MPa,which is increased by 24.7%,and the elongation is increased by 66.7%.(4)Ultrasonic and Y elements will improve the aging strengthening effect of Mg-12Gd-0.5Zr alloy.With the increase of ultrasonic power and Y content,the peak hardness and aging precipitation rate of Mg-12Gd-0.5Zr alloy gradually increase.Mg-12Gd-0.5Zr alloy is aged at 200℃ after 1500 W ultrasonic treatment and reaches its peak aging at 40 h.The Brinell hardness is 111 HBW.Compared with the aging treatment without ultrasonic treatment at 175 ℃,it reaches the peak aging at 100 h,and the hardness is 100.35 HBW.The peak hardness is increased by 10.6%,and the aging time is shortened by 150%.The peak aging of Mg-12Gd-5Y-0.5Zr alloy is 138.2 HBW compared with 111 HBW of Mg-12Gd-0.5Zr alloy which is increased by 24.5%. |
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