【作者】 张宏伟；

【导师】 王武孝； 曹智勇；

【作者基本信息】 西安理工大学 ， 材料工程（专业学位）， 2024， 硕士

【摘要】 Mg-Gd系稀土镁合金以其优异的力学性能被广泛应用在汽车、军事、航空航天领域。随着时代的发展,汽车以及飞机的零部件对力学性能的要求越来越高,在实际应用中,若将镁合金应用于汽车以及飞机的承力部件,仍有较大的断裂或失效的风险,这就需要进一步提升合金性能。一般情况下,高Gd含量的镁合金力学性能比较优异,但是过高的Gd含量会提升合金成本并且不利于轻量化,因此科研工作者们常常在Mg-Gd合金中添加其他元素以提高合金的力学性能,并且希望能在保持合金性能的基础上减少稀土元素的用量以降低成本。本文通过光镜(OM)、扫描电镜(SEM)、X射线衍射分析(XRD)和能谱分析(EDS)等手段研究了 Zn、Mn元素的添加对于Mg-10Gd合金显微组织及力学性能的影响;分析了Mg-10Gd-1.5Zn-xMn(x=0、0.5、1.0、1.5)合金的室温拉伸性能以及以及固溶态合金的高温压缩行为。使用0.5wt.%、1.0wt.%、1.5wt.%的Mn元素替代Gd元素后,对Mg-(10-x)Gd-1.5Zn-xMn(x=0、0.5、1.0、1.5)合金做了以上相同的分析。所得结论如下:(1)在Mg-10Gd合金中添加1.5wt.%的Zn元素后,典型的树枝晶转变为介于树枝晶与胞状晶之间的组织。在Mg-10Gd-1.5Zn合金中,随着Mn含量的增加,α-Mg枝晶的平均尺寸由73μm细化到39μm,在Mg-1 0Gd-1.5Zn-xMn合金中,显微组织主要由α-Mg、(Mg,Zn)3Gd、Mg5Gd、富Gd相以及α-Mn组成,当Mn含量为1.5wt.%时,铸态合金组织中出现了 18R-LPSO相,此时合金硬度达到81.3HV,屈服强度为103.52MPa,抗拉强度为 141.37MPa,相比于 Mg-10Gd-1.5Zn 合金,分别提高了 23.8%、9.35%、16.7%。(2)随着固溶处理时间由4h增加至16h,(Mg,Zn)3Gd相及其内部形貌逐渐发生变化,(Mg,Zn)3Gd相内部的棒状与短条状在固溶过程中逐渐变化成连续条状组织,12h时,其内部形成连续分布的鱼骨状,随着时间继续增加,(Mg,Zn)3Gd相内部形貌不再变化,(Mg,Zn)3Gd相转变为弥散分布的圆点状。固溶处理后组织中还形成了层片状14H-LPSO结构。随着固溶处理时间的增长,Mg-10Gd-1.5Zn-1.5Mn合金的力学性能先上升后下降,在12h时合金硬度为94.5HV,屈服强度达到121.81MPa,抗拉强度达到158.30MPa,16h相比于12h略微下降;(3)随着Mn含量的增加,固溶态Mg-10Gd-1.5Zn-xMn合金的枝晶尺寸得到细化,14H-LPSO结构体积分数由最初的12.855%增加到25.576%。固溶态Mg-10Gd-1.5Zn-xMn合金的力学性能逐渐上升,在Mn含量为1.0wt.%时达到顶峰,在Mn含量为1.5wt.%时与1.0 wt.%相比相差不大。(4)高温压缩实验表明,在Mn含量为1.0wt.%时,固溶态合金屈服强度与抗压强度分别达到 136.05MPa、239.65MPa,相比于 Mg-10Gd-1.5Zn 合金分别提升了 13.25%、16.63%;压缩温度由300℃提升到400℃,合金的屈服强度与抗压强度达到125.74MPa、221.28MPa,与300℃相比分别下降了 7.57%与7.66%。(5)使用 0.5wt.%、1.0wt.%、1.5wt.%的 Mn 元素替代 Gd 元素后,Mg-(10-x)Gd-1.5Zn-xMn合金与Mg-10Gd-1.5Zn-xMn合金相比,合金显微组织无显著变化,室温拉伸性能下降幅度为2%-6%,高温压缩性能下降幅度在2%-5%。更多还原

【Abstract】 Given its superior mechanical qualities,magnesium alloys with the Mg-Gd system of rare earth elements are widely employed in the automotive,military,and aerospace industries.As technology advances,an increasing number of mechanical qualities are required in both airplane and automotive components.In reality,there is still a greater probability of fracture or failure if magnesium alloys are used on the load-bearing components of cars and airplanes,necessitating further enhancement of the alloy’s qualities.Magnesium alloys with high Gd content generally have superb mechanical properties;nevertheless,an excessive Gd content will raise the alloys’ cost and hinder their ability to be lightweighted.As a consequence,researchers have frequently added other elements to Mg-Gd alloys to enhance the alloy’s mechanical properties,with the intention of reducing the amount of rare earth elements while maintaining alloys’ performance in a bid to cut costs.The optical microscope(OM),scanning electron microscope(SEM),X-ray diffraction analysis(XRD),energy dispersive spectrometer(EDS)were utilized in the present research.examine the effects of adding Zn and Mn elements on the microstructure and mechanical properties of Mg-10Gd alloys.The tensile properties of Mg-10Gd-1.5Zn-xMn(x=0.0.5,1.0,1.5)at room temperature and the high temperature compression behavior of the solid solution alloy were analyzed.For the Mg-(10-x)Gd-1.5Zn-xMn(x=0、0.5、1.0、1.5)alloys,the same study was performed using 0.5wt.%,1.0wt.%,and 1.5wt.%of Mn in place of the Gd element.The following are the conclusions that were reached:(1)The addition of 1.5wt.%Zn element in Mg-10Gd alloy caused the typical dendritic crystal to change into an microstructure between dendritic and cellular crystals.Additionally,the average size of the dendritic crystals of α-Mg was refined from 73 μm to 39 μm with the increase in Mn content in the Mg-10Gd-1.5Zn-xMn alloys.The microstructure of Mg-10Gd-1.5Zn-xMn alloy was mainly composed of α-Mg,(Mg,Zn)3Gd,Mg5Gd,Gd-rich phases,and α-Mn.The 18R-LPSO phase appeared in the as-cast alloy at 1.5wt.%Mn content.And the alloy hardness was 81.3 HV,yield strength was 103.52 MPa,and tensile strength was 141.37 MPa,which were 23.8%,9.35%,and 16.7%,respectively,higher than those of the Mg-10Gd-1.5Zn alloy.(2)The(Mg,Zn)3Gd phase and its internal morphology gradually altered as the solid solution treatment duration increased from 4 to 16 hours.During the solid solution procedure,the rods and short strips inside the(Mg,Zn)3Gd phase gradually converted into continuous strips.After 12 hours,the fishbone’s internal distribution took shape.With prolonged exposure,the(Mg,Zn)3Gd phase’s internal morphology remained unchanged and took on a diffuse,spherical distribution.Following treatment with a solid solution,the microstructure also developed a lamellar 14H-LPSO structure.The Mg-10Gd-1.5Zn-1.5Mn alloy’s mechanical properties elevated initially and then weakened as the solid solution treatment time expanded.The alloy’s hardness was 94.5 HV,yield strength was 121.81 MPa,and tensile strength was 158.30 MPa at a treatment duration of 12 hours,with a slight decrease at 16 hours compared to 12 hours of treatment.(3)The dendritic size of the solid solution Mg-11Gd-1.5Zn-xMn alloy became more refined with an increase in Mn content,and the volume percentage of the 14H-LPSO structure rose from 12.855%to 25.576%.The Mg-10Gd-1.5Zn-xMn alloy’s mechanical qualities after the solid solution grew steadily,peaked at 1.0%Mn concentration,and did not vary significantly from 1.0%to 1.5%Mn content.(4)The high temperature compression experiment shows that the yield strength and compressive strength of solid solution alloy reach 136.05MPa and 239.65MPa respectively when Mn content is 1.0wt.%,which are 13.25%and 16.63%higher than that of Mg-10Gd-1.5Zn alloy.When the compression temperature was raised from 300℃ to 400℃,the alloy’s yield strength and compressive strength reached 125.74MPa and 221.28MPa,respectively,which is 7.57%and 7.66%lower than that of 300℃.(5)The Mg-(10-x)Gd-1.5Zn-xMn(x=0、0.5、1.0、1.5)alloys showed no substantial variations in the microstructure,decreased in both room temperature tensile properties and high temperature compressive properties,with the former falling between 2%and 6%and the latter between 2%and 5%compared with the Mg-10Gd-1.5Zn-xMn alloys after employing 0.5%,1.0%,and 1.5%Mn elements to replace the Gd element.更多还原