热处理对Mg-3Sn-2Al-1Zn-5Li合金耐蚀性能的影响

对Mg-3Sn-2Al-1Zn-5Li合金进行了不同方式的热处理。利用电化学测试研究了不同热处理状态合金在3.5%NaCl溶液中的腐蚀电化学行为,并通过扫描电镜、能谱以及X射线衍射分析了合金腐蚀形貌及腐蚀产物的成分。结果表明:经固溶处理和时效处理后,合金的耐蚀性能有所提高,并且固溶态的Mg-3Sn-2Al-1Zn-5Li合金有着最佳的耐蚀性能;合金的腐蚀特征为丝状腐蚀,腐蚀产物主要为Mg(OH)_(2)。

间断直流磁场对Al-5Mg-3Zn-1Cu合金凝固组织和性能的影响

对Al-5Mg-3Zn-1Cu合金的凝固过程施加不同直流电压(0~300 V)和放电频率(0~20 Hz)以及占空比为30%的间断直流磁场,研究了间断直流磁场对其凝固组织及力学性能的影响。结果表明:间断直流磁场有效细化了合金的凝固组织,初生α-Al相由无磁场时的粗大枝晶变为细小的蔷薇状晶粒,第二相由粗大而连续的网格状结构变为细小而断续分布结构。随着直流电压的增加,合金的晶粒尺寸、第二相体积分数和长度均减小,抗压强度和断裂应变均先升后降;随着放电频率的增加,晶粒尺寸、第二相体积分数和长度均先减小后增大,抗压强度和断裂应变均先升后降。施加间断直流磁场后,合金的拉伸性能提高,断口中的准解理面减少,撕裂棱增多。当直流电压为200 V、放电频率为5 Hz时,合金的抗压强度和断裂应变最大,与无磁场时相比分别提高了31.6%和43%,抗拉强度和断后伸长率则分别提高了79.71%和83.3%。

固溶态Mg-3Zn-Y-1.5Nd-0.4Zr合金组织演变及力学性能优化

研究了固溶处理(T4处理)对Mg-3Zn-1Y-1.5Nd-0.4Zr合金的组织演变与力学性能的影响。采用X射线衍射,扫面电子显微镜和能谱仪对铸态及固溶态Mg-3Zn-1Y-1.5Nd-0.4Zr合金的微观组织进行分析,采用单轴拉伸测试和显微硬度测试对铸态及固溶态Mg-3Zn-1Y-1.5Nd-0.4Zr合金的力学性能进行测试。结果表明,铸态Mg-3Zn-1Y-1.5Nd-0.4Zr合金晶界处连续的第二相在固溶过程中发生断裂并球化现象,其综合力学性能先增加后减小。Mg-3Zn-1Y-1.5Nd-0.4Zr合金在490℃下保温26 h时力学性能最佳,其极限抗拉强度,屈服强度和伸长率分别为278.20 MPa,226.79 MPa和13.53%。固溶处理过程中,Mg-3Zn-1Y-1.5Nd-0.4Zr合金因为第二相发生球化现象,第二相中溶质元素的溶解产生固溶强化,使固溶态Mg-3Zn-1Y-1.5Nd-0.4Zr合金的综合力学性能得到提高。

Effect of heat treatment on microstructures and mechanical properties of sand-cast Mg-10Gd-3Y-0.5Zr magnesium alloy

The microstructure, mechanical properties and fracture behavior of sand-cast Mg-10Gd-3Y-0.5Zr alloy （mass fraction,%） under T6 condition （air cooling after solid solution and then aging heat treatment） were investigated. The optimum T6 heat treatments for sand-cast Mg-10Gd-3Y-0.5Zr alloy are （525 ℃, 12 h＋225 ℃, 14 h） and （525 ℃, 12 h＋250 ℃, 12 h） according to age hardening curve and mechanical properties, respectively. The ultimate tensile strength, yield strength and elongation of the Mg-10Gd-3Y-0.5Zr alloy treated by the two optimum T6 processes are 339.9 MPa, 251.6 MPa, 1.5%and 359.6 MPa, 247.3 MPa, 2.7%, respectively. The tensile fracture mode of peak-aged Mg-10Gd-3Y-0.5Zr alloy is transgranular quasi-cleavage fracture.

高塑性Mg-3Zn-1Y-1Mn合金在不同挤压温度下的组织演变、强化机制和变形行为

为了改善铸态Mg-3Zn-1Y-1Mn合金的力学性能、研究合金在不同变形温度下的组织演变规律和变形机理,对铸态Mg-3Zn-1Y-1Mn合金进行热挤压实验。实验结果显示,当挤压温度为330℃时,挤压态合金具有最佳的力学性能,抗拉强度和伸长率分别达到270 MPa和16.8%。挤压态合金性能大幅提高主要归因于3个方面:由动态再结晶导致的细晶强化作用、未被动态再结晶抵消的加工硬化以及第二相粒子强化作用。在热挤压过程中,当挤压温度为300℃时,同时发生连续动态再结晶和动态回复;而当挤压温度为330和360℃时,发生不连续动态再结晶。此外,在热变形过程中{0001}基面滑移、{10 10}Ⅰ型柱面滑移和{11 20}Ⅱ型柱面滑移对塑性变形的贡献受挤压温度影响很大,而{11 20}Ⅱ型柱面是3个滑移系中最难启动的滑移系。

Mg-3Zn-1Zr合金细径管材的挤压模具设计

基于Mg-3Zn-1Zr合金本构方程运用Defrom-3D软件对多种Mg-3Zn-1Zr合金细径管材的挤压模具参数的配合进行了有限元模拟分析。结果表明:挤压模入口圆角半径一定时,挤压模模角越大,挤压杆的载荷越小,挤压模圆锥段发生紊流现象越严重,挤压死区越大。挤压模入口圆角处的磨损最为严重,当挤压模模角为120°,挤压模入口圆角半径为2mm时,模具磨损最小,挤压载荷和模具应力也较小。工作带长度超过4mm时,随着工作带长度的增加,模具磨损深度显著增大,管材与模具易产生黏结,进而产生缺陷和变形不均匀。采用模拟优化的模具挤压出的Mg-3Zn-1Zr合金细径管材表面质量良好、尺寸精度高,说明基于Deform-3D有限元分析能够为实际模具设计与镁合金型材的生产提供可靠参考。

Mg-3Zn-1Zr合金热变形行为及其本构模型

采用Gleeble 3800热模拟机测试了Mg-3Zn-1Zr合金在温度为250～350℃、应变速率为0. 01～1 s-1条件下的多组热模拟压缩变形行为。结果表明:合金在热压缩时表现出明显的动态再结晶特征,随应变的增加流动应力先快速增加,然后经过一个缓慢的增加后达到峰值,最后极缓慢的下降并保持稳定。合金热变形时的流动应力对变形温度和变形速率非常敏感,随变形速率的增加而增大,随变形温度的升高而降低。利用热模拟压缩实验数据,基于Arrhenius方程和Zener-Hollomon参数,运用多元回归分析方法建立了Mg-3Zn-1Zr合金在高温变形过程中的流变应力本构模型。

均匀化退火处理对Mg-10Gd-4Y-1Zn-0.5Zr合金微观组织的影响

均匀化退火处理对Mg-Gd-Y-Zn-Zr合金的微观组织具有重要影响,特别是LPSO结构的演变对于稀土镁合金的推广应用具有重要的作用。为研究均匀化退火处理对Mg-Gd-Y-Zn-Zr合金组织演变的影响,采用氩气保护真空电阻炉熔铸Mg-10Gd-4Y-1Zn-0.5Zr(质量分数,%)铸棒,随后进行均匀化退火处理,并采用光学、扫描电子及透射电子显微镜对铸态和均匀化退火态试样进行显微组织分析。结果显示,铸造态试样由少量随机散布的孤岛状Mg5.05(Gd,Y,Zn)微粒相、粗大块状Mg10(Gd,Y)Zn共晶相、少量Mg-RE微粒相及大量粗壮基体α-Mg组成,平均晶粒尺寸为91.2μm;均匀化退火态合金由基体α-Mg和Mg12(Gd,Y)Zn及Mg-RE等第二相组成,平均晶粒尺寸为142.1μm。相较铸态,均匀化退火态晶粒发生显著生长,晶界处粗大的块状Mg5(Gd,Y,Zn)共晶相和18R-LPSO结构转变为晶粒内部细小层片状14H-LPSO结构,基体中的LPSO结构数量增多,形貌由粗大块状演变为密集细小的层片状,且未有高密度位错和第二相,表明均匀化退火过程有效促进了合金的软化,对后续塑性加工的进行有重要作用。

Mg-11Gd-3Y-1.1Zn-0.5Zr的高温热压缩行为及热加工图

采用Gleeble-1500热模拟试验机对均匀化后的Mg-11Gd-3Y-1.1Zn-0.5Zr合金进行了温度为350~500℃、应变速率为0.002~1 s-1的热压缩实验,构建了合金高温塑性变形的本构方程,建立并分析了合金的热加工图。结果表明:Mg-11Gd-3Y-1.1Zn-0.5Zr合金热变形发生了动态回复和动态再结晶,合金的流变应力随温度的升高和应变速率的降低而升高,合金热变形激活能Q=286.134 kJ/mol;合金在T=380~500℃、ε·=0.002~0.05 s-1区域能量耗散率大于30%且不发生失稳,适合热加工。

Low temperature mechanical properties of as-extruded Mg-10Gd-3Y-0.5Zr magnesium alloy

Influence of multi-cycle cryogenic treatment and tensile temperature on microstructure, mechanical properties and fracture mechanism of as-extruded Mg-10Gd-3Y-0.5Zr magnesium alloy was investigated. The results show that there have no significant changes in tensile properties of the tested alloy after 10 d in liquid nitrogen immersion or 10 cycles of high-low temperature treatment at all test temperatures. The room temperature ultimate tensile strength increases from 398 MPa to 417 MPa after 20 cycles of high-low temperature treatments. Compared with the room temperature, the tested alloys exhibit higher tensile properties at low temperatures. At -196 °C, the yield strength and ultimate tensile strength of the as-extruded-T5 Mg-10Gd-3Y-0.5Zr alloy are 349 MPa and 506 MPa, respectively, increasing by about 18% and 27%, respectively. The transgranular cleavage fracture mechanism is observed at room temperature, while at low temperatures both ductile fracture and cleavage fracture behaviors coexist.

Improved Corrosion Behavior of Biodegradable Mg-4Zn-1Mn Alloy Modified by Sr/F co-doped CaP Micro-arc Oxidation Coatings

The Sr/F co-doped CaP(Sr/F-CaP)coatings were prepared by micro-arc oxidation(MAO)under different voltages to modify the microstructure and corrosion behavior of Mg-4Zn-1Mn alloy.The surface and interface characteristics investigated using scanning electron microscopy(SEM)and energy dispersive X-ray spectrometer(EDS)showed that the MAO coatings displayed uneven crater-like holes and tiny cracks under lower voltage,while they exhibited relatively homogeneous crater-like holes without cracks under higher voltage.The thickness of MAO coatings increased with increasing voltage.The corrosion behavior of Mg-4Zn-1Mn alloy was improved by the MAO coatings.The MAO coatings prepared under 450 V and 500 V voltages possessed the best corrosion resistance with regard to the electrochemical corrosion tests and immersion corrosion tests,respectively.The MAO coatings fabricated under 450-500 V could provide a better corrosion protection effect for the substrate.

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。

Effects of Ce on microstructure of semi-continuously cast Mg-1.5Zn-0.2Zr magnesium alloy ingots

Mg-1.5Zn-0.2Zr-xCe (x=0, 0.1, 0.3, 0.5, mass fraction, %) alloys were prepared by conventional semi-continuous casting. The effect of rare earth Ce on the microstructure of Mg-1.5Zn-0.2Zr-xCe alloys was studied and the distribution of Ce was analyzed by optical microscopy (OM), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results indicate that Ce element exists in the form of Mg12Ce phase and has an obvious refining effect on the microstructure of test alloys. As the Ce content increases, the grain size reduces, the grain boundaries turn thinner, and the distribution of Mg12Ce precipitates becomes more and more dispersed. The Mg-1.5Zn-0.2Zr alloy with 0.3%Ce has the best refinement effect. From center to periphery of the ingot, the amount of granular precipitates in the grain reduces. In longitudinal section of the ingot, some relative long columnar grains appear.

Microstructure and mechanical properties of Mg-3.0Nd-0.4Zn-0.4Zr magnesium alloy

Mg-3.0Nd-0.4Zn-0.4Zr magnesium alloy were prepared by cast-extruding and chip-extruding.Microstructure,tensile and creep properties of the alloy were investigated.The results show that the alloy exhibit particle dynamic recrystallization during extrusion.The cast extruded-T6 rods at room temperature have a highest tensile strength of 258.5 MPa and a highest yield strength of 135.7 MPa.With the increase of test temperature,the strength of the alloy declines and the elongation increases.At 473 K,creep strain in the primary creep stage increases with increasing the creep stresses.Under 110 MPa,time spent during primary creep decreases with increasing the test temperatures.Stress exponent and creep activation energy of the alloy are 4.4 and 104 kJ/mol,respectively.Creep of the alloy can be controlled by dislocation climb mechanism.The morphology of the fracture surfaces was examined by employing scanning electron microscope.

Residual stress and precipitation of Mg-5Zn-3.5Sn-1Mn-0.5Ca-0.5Cu alloy with different quenching rates

The effect of the quenching rate after solution treatment on the residual stress and precipitation behavior of a high strength Mg-5 Zn-3.5 Sn-1 Mn-0.5 Ca-0.5 Cu plate is studied.The simulation results show decreasing temperature gradient in the plate with decreasing quenching rate,which leads to weakened inhomogeneous plastic deformation and decreased residual stress.No dynamic precipitation on the grain boundary happens after either cold water cooling or air cooling,however,air cooling leads to dynamic precipitation of Mg-Zn phase on Mn particles around which a low-density precipitate zone develops after aging treatment.Moreover,the fine and densely distributed Mg-Zn precipitates observed after aging treatment of the cold water cooled alloy are replaced by coarse precipitates with low density for the air cooled alloy.Both the low-density precipitate zone near Mn particles and the coarsening of precipitates are the source of the decrease in hardness and tensile properties of the air cooled alloy.The residual stress drops faster than the hardness with decreasing quenching rate,which makes it possible to lower the residual stress without sacrificing too much age-hardening ability of the alloy.

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.

Effects of Mg content on microstructure and mechanical properties of low Zn-containing Al-xMg-3Zn-1Cu cast alloys

Effects of Mg content on the microstructure and mechanical properties of low Zn-containing Al−xMg−3Zn−1Cu cast alloys(x=3−5,wt.%)were investigated.As Mg content increased in the as-cast alloys,the grains were refined due to enhanced growth restriction,and the formation ofη-Mg(AlZnCu)_(2) and S-Al_(2)CuMg phases was inhibited while the formation of T-Mg_(32)(AlZnCu)_(49 )phase was promoted when Mg content exceeded 4 wt.%.The increase of Mg content encumbered the solution kinetics by increasing the size of eutectic phase but accelerated and enhanced the age-hardening through expediting precipitation kinetics and elevating the number density of the precipitates.As Mg content increased,the yield strength and tensile strength of the as-cast,solution-treated and peak-aged alloys were severally improved,while the elongation of the alloys decreased.The tensile strength and elongation of the peak-aged Al−5Mg−3Zn−1Cu alloy exceed 500 MPa and 5%,respectively.Precipitation strengthening implemented by T′precipitates is the predominant strengthening mechanism in the peak-aged alloys and is enhanced by increasing Mg content.

Effect of different casting methods on microstructure and mechanical properties of Mg-10Gd-3Y-0.6Zr alloy

The effects of two different casting methods on the microstructures and mechanical properties of as-cast and T6-cast states of Mg-10Gd-3Y-0.6Zr alloy were studied by using metal mold casting and squeeze casting.The results show that the microstructure of Mg-10Gd-3Y-0.6Zr alloy is mainly composed ofα-Mg primary phase and Mg 24(Gd,Y)5 eutectic phase.The squeeze cast grains are small with a dendrite like morphology,and the tensile strength of the alloy in T6 state can reach 285 MPa.While the metal grains are coarse,the eutectic phases are distributed in the grain boundary,and the tensile strength of the alloy in T6 state is only 250 MPa.

Effects of Ce addition on microstructure and mechanical properties of Mg-6Zn-1Mn alloy

The effects of Ce addition on the microstructure of Mg-6Zn-1Mn alloy during casting, homogenization, hot extrusion, T4, T6 and T4＋two-step aging were investigated. The mechanical properties of alloys with and without Ce were compared. The results showed that Ce had an obvious effect on the microstructure of ZM61-0.5Ce alloy by restricting the occurrence of dynamic recrystallization and restraining the grain growth during extrusion and heat treatment subsequently. A new binary phase Mg 12 Ce was identified in ZM61-0.5Ce alloy, which distributed at grain boundaries and was broken to small particles distributed at grain boundaries along extrusion direction during extrusion. The mechanical properties of as-extruded ZM61-0.5Ce alloy were improved with the addition of Ce. The improved tensile properties of as-extruded ZM61-0.5Ce alloy were due to the finer grain sizes as compared to ZM61 alloy. However, the UTS and YS decreased severely and the elongation increased when ZM61-0.5Ce was treated by T6 and T4＋two-step aging. Brittle Mg 12 Ce phase, which was distributed at the grain boundary areas and cannot dissolve into the Mg matrix after solution treatment, became crack source under tensile stress.

Effect of heat treatment on microstructures and mechanical properties of sand-cast Mg-4Y-2Nd-1Gd-0.4Zr magnesium alloy

Influence of heat treatment on the microstructures and mechanical properties of sand-cast Mg-4Y-2Nd-1Gd-0.4Zr magnesium alloy was investigated,and the tensile fracture mechanisms of the studied alloys under different conditions were also discussed.The results show that the optimum T4 and T6 heat treatment conditions for the as-cast Mg-4Y-2Nd-1Gd-0.4Zr alloy are 525°C,8 h and（525°C,8 h）＋（225°C,16 h）,respectively,with regard to the microstructure observation,DSC heating curve and mechanical properties.The hardness,yield strength,ultimate tensile strength and elongation of the Mg-4Y-2Nd-1Gd-0.4Zr alloy treated by optimum T6 heat treatment are HV91,180 MPa,297 MPa and 7.4%,respectively.Moreover,the Mg-4Y-2Nd-1Gd-0.4Zr alloys under different heat treatment conditions exhibit different tensile fracture modes.