Microstructure evolution of semi-solid Mg-10Gd-3Y-0.5Zr alloy during isothermal heat treatment

In this study,the microstructure evolution of semi-solid Mg-10Gd-3Y-0.5Zr alloy during isothermal heat treatment has been investigated.The results show that primary particles coarsen continuously during the holding.Coarsening rate decreases with the increase of isothermal temperature.When isothermal temperature increases from 600℃ to 620℃,the dominant mechanism for coarsening changes from particle coalescence to Ostwald ripening.Equiaxed as-cast microstructure is beneficial to the semi-solid microstructure after isothermal heat treatment,which brings about the refinement and spheroidization of primary particles,and shortening of holding time.Significant modification of second phases can also be achieved after isothermal heat treatment,due to its unique solidification process.The optimum processing parameters for Mg-10Gd-3Y-0.5Zr alloy in isothermal heat treatment are isothermal temperature of 610℃-620℃ and holding time of 20-40 min.

Effect of heat treatment on corrosion behavior of low pressure sand cast Mg-10Gd-3Y-0.5Zr alloys

The corrosion behaviors of low-pressure sand cast Mg-10Gd-3Y-0.5Zr(wt.%) alloys in as-cast, solution treated(T4) and aged(T6) conditions were studied by means of immersion test and electrochemical measurements in 5wt.% NaCl solution saturated with Mg(OH)_2. It was observed that the corrosion rate in the T4 condition was lower than that of the as-cast and T6 conditions by both sand casting and permanent mold casting with the same order of as-cast>T6>T4; while the corrosion resistance of the permanent mold casting is superior to the sand casting. The morphologies of the corrosion products are similar porous structures consisting of tiny erect flakes perpendicular to the corroded surface of the alloy, irrespective of the heat treatment conditions. Especially, the corrosion film in T4 condition is more compact than that in the other two conditions. In addition, the severer corrosion happening to the as-cast condition is correlated with the galvanic corrosion between the matrix and the eutectic compounds; while improved corrosion resistance for the T4 and T6 conditions is ascribed to the dissolution of the secondary eutectic compounds. The measured corrosion current densities of Mg-10Gd-3Y-0.5Zr alloys in as-cast, T4, and T6 conditions are 36 μA?cm^(-2), 10 μA?cm^(-2), and 33 μA?cm^(-2), respectively. The proposed equivalent circuit [Rs(CPE_1(R_t(R_fCPE_2))] by Zview software matches well with the tested electrochemical impedance spectra(EIS) data.

热处理对砂型铸造Mg-10Gd-3Y-0.5Zr镁合金微观组织和力学性能的影响（英文）

采用金相分析、SEM、硬度试验和拉伸试验等方法分析和测试砂型铸造Mg-10Gd-3Y-0.5Zr镁合金在T6态(固溶后空冷然后时效)下的显微组织和室温力学性能,讨论该合金的断裂机理。结果表明,砂铸Mg-10Gd-3Y-0.5Zr合金在225°C和250°C时效下的最优T6热处理工艺分别为(525°C,12 h+225°C,14 h)和(525°C,12 h+250°C,12 h)。峰时效下T6态Mg-10Gd-3Y-0.5Zr合金主要由α-Mg+γ+β′相组成,2种峰时效热处理工艺下合金的抗拉强度、屈服强度和伸长率分别为339.9 MPa、251.6 MPa、1.5%及359.6 MPa、247.3 MPa、2.7%。在不同热处理工艺下Mg–10Gd–3Y–0.5Zr合金断裂的类型不同,峰时效态合金的断裂方式为穿晶准解理断裂。

冷却速率对砂型铸造Mg-10Gd-3Y-0.4Zr合金凝固行为的影响(英文)

采用计算机辅助冷却曲线分析技术研究砂型铸造过程中冷却速率(1.4~3.5°C/s)对Mg-10Gd-3Y-0.4Zr合金凝固行为的影响。结果表明:随着冷却速率的提高,起始形核温度(Tα,N)由634.8°C升至636.3°C,再辉前最低温度(Tα,Min)由631.9°C降至630.7°C,形核过冷度(ΔTN)由2.9°C升至5.6°C,共晶反应起始温度(Teut,N)上升,固相线温度(T S)由546.0°C降至541.4°C,凝固温度区间(ΔTS)增加6.1°C。形核速率(N)的增加引起晶核数量的增加,从而降低α-Mg的平均晶粒粒径。相对于形核时间(ΔtN),形核过冷度(ΔTN)对α-Mg平均晶粒粒径的影响更大。温度增加值(T eut,N-T eut,G)与缩短的反应时间改变共晶反应进程,并且影响第二相的含量以及形貌。

时效时间对Mg-10Gd-3Y-0.5Zr镁合金力学性能的影响

选取了在工程实践中有广泛应用的Mg-10Gd-3Y-0.5Zr镁合金,在225℃下对合金进行了时效处理,研究了时效时间对合金力学性能的影响。结果表明：在6、8、10、12、14、16 h时效时效范围,合金的硬度、抗拉强度和屈服强度在12 h处理之后达到最大值。

Zn对铸态Mg-10Gd-3Sm-0.5Zr合金组织和力学性能的影响

采用熔炼铸造法制备了添加0~2%Zn(质量分数)的Mg-10Gd-3Sm-0.5Zr合金,通过X射线衍射、扫描电镜和拉伸性能测试等分析了Zn对铸态Mg-10Gd-3Sm-0.5Zr合金组织与性能的影响。结果表明:铸态Mg-10Gd-3Sm-0.5Zr合金由粗大枝晶α-Mg基体和晶界处半连续分布稀土相Mg41(Sm,Gd)5和Mg5Gd(Sm)组成,加入Zn元素后,在合金中产生了新相(Mg,Zn)3(Sm,Gd)1;铸态Mg-10Gd-3Sm-xZn-0.5Zr合金室温拉伸力学性能随着Zn元素含量的增加先升高后降低,当Zn的添加量为1%时,综合力学性能最好,其抗拉强度、屈服强度、伸长率分别为215 MPa、173 MPa和5.5%;合金的断裂方式主要为脆性断裂,加入Zn元素后有向韧性断裂转变的趋势。

热轧及退火处理对Mg-10Gd-3Y-0.3Zr合金显微组织及抗压强度的影响

为了探究Mg-10Gd-3Y-0.3Zr高温热轧及退火处理对合金显微组织及抗压强度的影响,文中利用光学金相显微镜观察高温轧制板材的显微组织,分析晶粒尺寸大小和动态再结晶程度.研究结果表明:随着变形量增加,晶粒尺寸显著减小,当下压量为60%时晶粒尺寸大小均匀,约为60μm,孪晶密度高;下压量达到60%之前,晶粒粗大,孪晶密度低,超过60%之后,再结晶晶粒逐步取代变形晶粒,晶粒尺寸减小,孪晶几乎消失.退火处理能够显著提高轧制板材的抗压强度,其中175℃×3h退火处理后强化效果明显,抗压强度达到424MPa,退火温度超过175℃后,强化效果开始减弱.

挤压态Mg-10Gd-3Y-0.5Zr镁合金的低温力学性能(英文)

研究多循环低温交变(液氮浸泡处理)和拉伸温度对挤压态Mg10Gd3Y0.5Zr镁合金的微观组织、力学性能以及断裂机制的影响。结果表明,Mg10Gd3Y0.5Zr合金经10d液氮浸泡或10个周期高低温交变循环后,合金室温力学性能基本不变;而经过20个周期高低温循环后,合金的室温抗拉强度由398MPa升高到417MPa。在196°C下拉伸时,挤压态Mg10Gd3Y0.5Zr镁合金的屈服强度和抗拉强度均大幅度提高,分别为349MPa和506MPa,分别增长了18%和27%。合金室温断裂机制为穿晶解理断裂,而低温条件下为韧性断裂和解理断裂并存的混合断裂机制。

Mg-10Gd-3Sm-1Zn-0.5Zr合金热压缩变形行为及加工图

采用熔炼铸造法制备了Mg-10Gd-3Sm-1Zn-0.5Zr合金,对合金均匀化处理后进行热压缩实验,研究了合金在温度623~773 K、应变速率0.002~1 s^(-1)、最大变形量70%条件下的热变形行为,计算了合金的热变形激活能,建立了合金的热压缩变形本构方程和热加工图并进行了分析。结果表明:当温度从623 K提高到723 K,应变速率为0.01 s^(-1)时,峰值应力从194.89 MPa降为71.59 MPa。当温度为723 K,应变速率从1 s^(-1)降低到0.01 s^(-1)时,峰值应力从127.49 MPa下降到71.56 MPa;经计算,合金的热变形激活能为290.45 kJ·mol^(-1);合金最优加工工艺为:温度623~773 K,应变速率0.002~0.007 s^(-1),合金存在一个热加工失稳区:温度658~758 K,应变速率0.08~1 s^(-1),热加工时应避开此区域。

不同铸造方法对Mg-10Gd-3Y-0.6Zr合金组织形貌及力学性能的影响（英文）

采用金属型和挤压铸造两种不同铸造方法对铸态和T6态Mg-10Gd-3Y-0.6Zr合金的组织形貌和力学性能进行研究。结果表明,Mg-10Gd-3Y-0.6Zr合金铸态组织主要由α-Mg初生相和Mg24(Gd,Y)5共晶相组成;挤压铸造所得合金晶粒细小,且呈枝晶状形貌,T6态时合金抗拉强度可达285MPa;金属型所得合金晶粒较粗大,共晶相呈网状分布在晶界处,T6态时合金抗拉强度只有250 MPa。

不同热处理下Mg-10Gd-3Y-0.5Zr合金拉伸力学性能统计分析

在不同热处理工艺参数下研究了Mg-10Gd-3Y-0.5Zr合金力学性能的统计学变化规律。结果表明,Mg-10Gd-3Y-0.5Zr合金在高温服役时拉伸力学性能的稳定性变差。525℃×12 h+225℃×14 h处理工艺比525℃×12 h+250℃×12 h处理工艺更能使合金满足性能要求。

Zn对Mg-10Gd-3Sm-0.5Zr合金热压缩行为的影响

采用熔炼铸造法制备了添加0%-2%Zn(质量分数)的Mg-10Gd-3Sm-0.5Zr合金,对其固溶处理后进行热压缩试验,研究合金在温度350-500℃,应变速率0.002-1s^(-1),最大变形量70%条件下的热变形行为,计算了其热变形激活能,建立了合金的热压缩变形本构方程和热加工图并进行了分析。结果表明:加入Zn元素后,合金的峰值应力先升高后减小,加入1%Zn元素的峰值应力最高;未添加Zn的合金的热激活能为256.87 kJ/mol,加入1%Zn后合金的热激活能为290.45 kJ/mol;添加Zn元素后,合金的热加工图失稳区减小,可加工面积增大,高温时热压缩的组织更加细小均匀。

挤压态Mg-10Gd-3Y合金动态维氏硬度的研究

研究了挤压态Mg-10Gd-3Y合金的动态维氏硬度,分析了压痕周围的微观组织,并与静态维氏硬度值进行对比。结果表明:挤压态Mg-10Gd-3Y合金动态维氏硬度高于静态维氏硬度,表现出明显的应变率正效应,并且其动态维氏硬度随应变量的增加出现一个极大值,压痕周围出现孪晶组织,随应变量的增加孪晶数量减少。

Grain refinement impact on the mechanical properties and wear behavior of Mg-9Gd-3Y-2Zn-0.5Zr alloy after decreasing temperature reciprocating upsetting-extrusion

Based on the deforming technique of severe plastic deformation(SPD), the grain refinement of a Mg-9Gd-3Y-2Zn-0.5Zr alloy treated with decreasing temperature reciprocating upsetting-extrusion(RUE) and its influence on the mechanical properties and wear behavior of the alloy were studied. The RUE process was carried out for 4 passes in total, starting at 0 ℃ and decreasing by 10 ℃ for each pass. The results showed that as the number of RUE passes increased, the grain refinement effect was obvious, and the second phase in the alloy was evenly distributed. Room temperature tensile properties of the alloy and the deepening of the RUE degree showed a positive correlation trend, which was due to the grain refinement, uniform distribution of the second phase and texture weakening. And the microhardness of the alloy showed that the microhardness of RUE is the largest in 2 passes. The change in microhardness was the result of dynamic competition between the softening effect of DRX and the work hardening effect. In addition, the wear resistance of the alloy showed a positive correlation with the degree of RUE under low load conditions. When the applied load was higher, the wear resistance of the alloy treated with RUE decreased compared to the initial state alloy. This phenomenon was mainly due to the presence of oxidative wear on the surface of the alloy, which could balance the positive contribution of severe plastic deformation to wear resistance to a certain extent.

Effect of Isothermal Forging on the Microstructure and Mechanical Properties of Mg-8Gd-3Y-0.5Zr Alloy

Aiming at the problems of poor plastic forming ability,narrow forging temperature range,and strain rate sensitivity of rare earth magnesium alloys,a study on the microstructure and mechanical properties of Mg-8Gd-3Y-0.5Zr alloy with different isothermal forging processes is carried out.The microstructure and properties of the alloy in the as-cast,isothermal forged,and post-aging states after forging are studied with optical microscope(OM),scanning electron microscope(SEM),and tensile testing.The results show that significant dynamic recrystallization occurs during the isothermal forging process,a fine equiaxed grain structure is formed,and the mechanical properties of the alloy are greatly improved.When the isothermal forging temperature is 460℃ and the strain rate is 0.02 s^(-1),the alloy structure performance is the best,the room temperature tensile yield strength(TYS)is 218 MPa,the ultimate tensile strength(UTS)is 299 MPa,and the fracture elongation(FE)is 19.2%.When the alloy is post-forging artificial aged,theα-Mg matrix is dispersed,the Mg_5(Gd,Y)phase is precipitated,the UTS of the alloy is increased to 392 MPa,and the FE is reduced to 12.0%.

(Y,Gd)H_(2) phase formation in as-cast Mg-6Gd-3Y-0.5Zr alloy

In this work,a new(Y,Gd)H_(2) precipitate was identified and systematically investigated in the as-cast Mg-6Gd-3Y-0.5Zr alloy by XRD,SEM with EDS,TEM with EDS techniques and thermodynamics analysis.Results show that the as-cast alloy contains α-Mg,Mg_(24)(Gd,Y)_(5),and(Y,Gd)H_(2) phase.The(Y,Gd)H_(2) phase usually forms near the eutectic phase Mg_(24)(Gd,Y)_(5) or in the α-Mg grains,displaying a rectangle-shape.The Mg_(24)(Gd,Y)_(5) and(Y,Gd)H_(2) phases crystalize in bcc and fcc structure,respectively,and the(Y,Gd)H_(2) phase has a semi-coherent relationship with α-Mg matrix.The thermodynamics calculation results reveal that the hydrogen dissolved in the melt leads to the formation of hydrides.It is also found that the(Y,Gd)H_(2) hydride can form directly from the liquid phase during solidification.Additionally,it can precipitate by the decomposition of Mg_(24)(Gd,Y)_(5) phase due to absorbing hydrogen from the remaining melt.

熔剂净化对Mg-Gd-Y-Zr合金流动性的影响

研究了RJ-6、RJ-6+5%GdCl3、RJ-6+5%YCl3以及JDMJ+X%GdCl3、JDMJ+X%YCl3熔剂精炼对Mg-10Gd-3Y-Zr合金流动性的影响,并采用了定量分析方法对精炼后的流动性试样进行夹杂物分析。试验结果表明:JDMJ+5%YCl3精炼剂和RJ-6+5%GdCl3精炼剂能显著提高合金的流动性,相对无熔剂精炼,流动性试样长度分别由780mm增加至1270mm和1113mm。夹杂物分析结果表明:JDMJ+5%YCl3精炼剂和RJ-6+5%GdCl3精炼剂能有效去除合金中的夹杂物,降低熔体的粘度,显著提高合金流动性。

Mg-Gd-Y-Zr合金的热裂性能

分别采用约束热裂棒法、热裂环法以及热裂综合测试系统来评定Mg-10Gd-3Y-Zr合金的热裂倾向性,并与常用AZ91D镁合金的热裂性能进行了比较。研究发现,Mg-10Gd-3Y-Zr合金和AZ91D合金的热裂倾向性为:约束热裂棒法评定的热裂倾向系数分别为8和32,热裂综合测试系统测定其抗热裂力分别约为340N和40N,热裂环法测定Mg-10Gd-3Y-Zr合金和AZ91D合金的临界断裂直径分别为53mm和48mm。试验结果表明,Mg-10Gd-3Y-Zr合金的热裂倾向性低于AZ91D合金的热裂倾向性。

净化及浇注工艺因素对Mg-Gd-Y-Zr合金流动性的影响

研究了JDMJ、JDMJ+5%YCl3和JDMJ+10%YCl3精炼剂、浇注温度以及覆膜砂型和金属型对Mg-10Gd-3Y-Zr合金流动性的影响。研究结果表明,JDMJ+5%YCl3精炼剂能显著提高合金的流动性,相对无熔剂精炼,金属型流动性试样的长度由780mm增加至1270mm。合金的流动性随浇注温度的升高而提高,当浇注温度由690℃升高到770℃时,金属型流动性试样的长度由595mm增加至995mm。研究结果还表明,覆膜砂型更有利于提高合金的流动性。

冷却速度对Mg-Gd-Y-Zr合金组织和固溶行为的影响

通过金相显微镜、扫描电镜、X射线衍射、差热(DTA)分析等手段,研究了砂型差压铸造和金属型Mg-10Gd-3Y-Zr合金的组织和固溶行为差异。结果表明,与金属型相比,砂铸Mg-10Gd-3Y-Zr合金的晶粒明显粗大,而第二相含量则相对较少;冷却速度不仅影响了合金的铸态组织,同时也影响了合金随后的固溶行为。金属型条件下,500℃×8h的热处理已使第二相达到完全固溶,而砂型铸造合金则需525℃×8h的高温固溶才能使第二相溶解完全。