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.

超声处理制备的生物可降解Zn-1Mg-0.5Ca合金的微观组织与腐蚀行为

锌合金不仅具有良好的生物相容性,而且还有较好的降解行为,成为近些年来国内外研究者关注的热点。但是,不管在力学性能上,还是在腐蚀性能上,铸态锌合金皆不具备人体植入金属材料的条件。所以,为了提升与优化锌合金的力学性能,同时符合植入人体后的腐蚀速率需求,本实验研究了不同超声功率(300 W,600 W,900 W)处理对的Zn-1Mg-0.5Ca合金微观组织及腐蚀性能的影响。研究结果表明:随着超声功率的增加,Zn-1Mg-0.5Ca的初生α-Zn树枝晶,片层的共晶Mg2Zn11相以及块状的CaZn13相被有效细化,初生α-Zn相由粗大的树枝晶转变为细小的等轴枝晶。粗大的多边形状CaZn13相被细化为细小的粒状,平均尺寸从34μm减小到5μm,片层的共晶Mg2Zn11相转变成细小的棒状和粒状。电化学测试表明:未经超声处理的Zn-1Mg-0.5Ca合金的腐蚀速率最低,为0.190 mm·a-1。随着超声功率的增加,合金的腐蚀速率逐渐增加,当超声功率达到900 W时,合金的腐蚀速率达到了0.490 mm·a-1。将样品浸泡15 d后的实验发现,未经超声处理的Zn-1Mg-0.5Ca合金的腐蚀速率低于超声处理合金的腐蚀速率,且随着超声功率的增加,合金腐蚀速率从0.144 mm·a-1增加到0.263 mm·a-1。

ECAP和时效对Mg-4Zn-1Mn-0.5Ca合金组织和性能的影响

将铸态Mg-4Zn-1Mn-0.5Ca合金在300℃热挤压成棒材,对棒材进行180℃时效处理和200℃等通道转角挤压(ECAP)。研究了热挤压合金、ECAP 8道次合金和时效后ECAP 8道次合金的组织和性能。随后对试样进行室温和150℃低温单轴拉伸。结果表明:8道次ECAP后合金比热挤压态合金具有更细、更均匀的晶粒组织,同时提高了合金的室温屈服强度。时效后ECAP 8道次合金的150℃断裂伸长率比未时效ECAP8道次合金提高17.4%,说明时效处理对合金性能起着重要作用。

Microstructures and mechanical properties of as-extruded and heat treated Mg-6Zn-1Mn-4Sn-1.5Nd alloy

The microstructures and mechanical properties of Mg-6Zn-1Mn-4Sn-1.5Nd alloy subjected to extrusion and T5 treatment were investigated using optical microscopy（OM）, X-ray diffractometer（XRD）, scanning electron microscopy（SEM）, electron back scattered diffraction（EBSD）, transmission electron microscopy（TEM）, hardness tests and uniaxial tensile tests. The results showed that the as-cast alloy consisted of α（Mg）, Mn, Mg7Zn3, Mg2 Sn and Mg Sn Nd phases. Dynamic recrystallization has completed during the extrusion process and the average grain size was 7.2 μm. After T5 treatment, the strength increased obviously, the yield strength and ultimate tensile strength of as-extruded alloy were increased by 94 and 34 MPa, respectively. Microstructure characterization revealed that the improvement of strength was determined by the high number density of β′1 rods.

Microstructure of Mg-8Zn-4Al-1Ca aged alloy

The microstructure of Mg-8Zn-4Al-1Ca aged alloy was investigated by TEM and HRTEM. The results show that the hardening produced in the Mg-8Zn-4Al-1Ca alloy is considerably higher than that in the Mg-8Zn-4A1 alloy. A dense dispersion of disc-like Ca2Mg6Zn3 precipitates are formed in Mg-8Zn-4Al-1Ca alloy aged at 160 ℃ for 16 h. In addition, the lattice distortions, honeycomb-looking Moir＆#233; fringes, edge dislocations and dislocation loop also exist in the microstructure. The precipitates of alloy aged at 160 ℃ for 48 h are coarse disc-like and fine dispersed grainy. When the alloy is subjected to aging at 160 ℃ for 227 h, the microstructure consists of numerous MgZn2 precipitates and Ca2Mg6Zn3 precipitates. All the analyses show that Ca is a particularly effective trace addition in improving the age-hardening and postponing the formation of MgZn2 precipitates in Mg-8Zn-4Al alloy aged at 160 ℃.

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)。

Effects of cooling rate on bio-corrosion resistance and mechanical properties of Mg-1Zn-0.5Ca casting alloy

Mg?1Zn?0.5Ca alloys were prepared by traditional steel mould casting and water-cooled copper mould injection casting at higher cooling rate. Microstructure, mechanical properties and bio-corrosion resistance of two alloys were contrastively investigated. Grain size reduces remarkably and microstructure becomes homogenous when raising cooling rate. The bio-corrosion behaviour in 3.5% sodium chloride solution (3.5% NaCl) and Hank’s solution at 37°C was investigated using electrochemical polarization measurement and the results indicate that the alloy prepared at higher cooling rates has better corrosion resistance in both types of solution. Further mass loss immersion test in Hank’s solution reveals the same result. The reason of corrosion resistance improvement is that raising cooling rate brings about homogeneous microstructure, which leads to micro-galvanic corrosion alleviation. The tensile test results show that yield strength, ultimate tensile strength and elongation are improved by raising cooling rate and the improvement is mainly due to grain refinement.

Effect of ultrasonic melt treatment on degassing of Mg-6Zn-1Ca alloy

The effect of ultrasonic power and treatment time on degassing of Mg-6Zn-1Ca alloy was studied in this paper. The degassing effect was characterized by measuring densities of ingots. The results show that proper ultrasonic treatment can remove hydrogen from the melt of the Mg-6Zn-1Ca alloy. The ultrasonic degassing effect is closely related to the ultrasonic power density and treatment time. The degassing efficiency increases with an increase in ultrasonic power density when the melt is treated at 690 °C for 120 s, reaching its highest value at 1.2 W·cm-3. When the power density is 1.2 W·cm-3, with an increase in ultrasonic treatment time, the degassing efficiency increases at first, reaches its peak value at 120 s, then decreases as the ultrasonic treatment is further prolonged. In this experiment, the optimum degassing effect with an efficiency of 67.5 % is obtained by ultrasonic treatment with the power density of 1.2 W·cm-3 for 120 s. The maximum density of ingot can be increased from 1.8069 g·cm-3 to 1.8146 g·cm-3(increased by 0.43%).

Microstructures and properties in surface layers of Mg-6Zn-1Ca magnesium alloy laser-clad with Al-Si powders

Laser surface cladding with Al-Si powders was applied to a Mg-6Zn-1Ca magnesium alloy to improve its surface properties.The microstructure,phase components and chemical compositions of the laser-clad layer were analyzed by using X-ray diffractometry(XRD),scanning electron microscopy(SEM)and energy dispersive spectrometry(EDS).The results show that the clad layer mainly consists ofα-Mg,Mg2Si dendrites,Mg17Al12and Al3Mg2phases.Owing to the formation of Mg2Si,Mg17Al12and Al3Mg2intermetallic compounds in the melted region and grain refinement,the microhardness of the clad layer(HV0.025310)is about5times higher than that of the substrate(HV0.02554).Besides,corrosion tests in the NaCl(3.5%,mass fraction)water solution show that the corrosion potential is increased from-1574.6mV for the untreated sample to-128.7mV for the laser-clad sample,while the corrosion current density is reduced from170.1to6.7μA/cm2.These results reveal that improved corrosion resistance and increased hardness of the Mg-6Zn-1Ca alloy can be both achieved after laser cladding with Al-Si powders.

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.

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.

Effects of yttrium and strontium additions on as-cast microstructure of Mg-14Li-1Al alloys

Mg-14Li-1Al （LA141）, LA141-0.3Y, LA141-0.3Sr, and LA141-0.3Y-0.3Sr alloys were prepared in an induction furnace in the argon atmosphere. The microstructures of these alloys were investigated through scanning electron microscope （SEM）, X-ray diffractometer （XRD） and energy dispersive spectrometer （EDS）. The results show that yttrium and/or strontium additions produce a strong grain refining effect in LA141 alloy. The mean grain sizes of the alloys with addition of Y and/or Sr are reduced remarkably from 600 to 500, 260, 230 μm, respectively. Al 2 Y, Al 4 Sr and Mg 17 Sr 2 phases with different morphologies are verified and exist inside the grain or at the grain boundaries, thus possibly act as heterogeneous nucleation sites and pin up grain boundaries, which restrain the grain growth.

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.

Comparative study on corrosion behavior of as-cast and extruded Mg-5Y-7Gd-1Nd-0.5Zr alloy in 5% NaCl aqueous solution

The corrosion behaviours of Mg-5Y-7Gd-1Nd-0.5Zr magnesium alloys prepared by as-casting and extrusion were investigated in 5% NaCl aqueous solution by immersion and electrochemical tests. The microstructure indicates the mean grain size of 15 μm for the extruded and 100 μm for the as-cast Mg-5Y-7Gd-1Nd-0.5Zr magnesium alloys. The corrosion morphology of as-cast sample shows pitting corrosion and little filiform corrosion, but that of the extruded sample shows pitting corrosion at the initial stage. The corrosion rate of extruded sample is higher than that of as-cast Mg-5Y-7Gd-1Nd-0.5Zr alloy according to the immersion test. The second phases containing RE acting as cathodes improve the corrosion properties. The corrosion potentials of as-cast and extruded Mg-5Y-7Gd-1Nd-0.5Zr alloys are -1.658 V and -1.591 V, respectively. The origins of the distinctive corrosion behavior of as-cast and extruded Mg-5Y-7Gd-1Nd-0.5Zr Mg alloys were discussed.

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%。

汽车零件用差压铸造Mg-9Al-1Zn-0.5Ca镁合金的组织及性能

采用差压铸造进行了汽车零件用镁合金Mg-9Al-1Zn-0.5Ca的制备,对组织、力学性能和耐磨损性能进行了测试与分析。结果表明:与重力铸造试样相比,差压铸造试样的抗拉强度提高9.7%,屈服强度提高12.5%,断后伸长率从8.8%增大到9.5%,磨损体积减小38.9%;差压铸造可以明显改善合金内部组织,提高合金的力学性能和耐磨损性能。

TEM microstructure of rapidly solidified Mg-6Zn-1Y-1Ce alloy

Rapidly solidified（RS） Mg-6Zn-1Y-1Ce ribbons were prepared by single roller melt-spinning technique.Transmission electron microscopy and energy dispersive X-ray spectroscopy were employed to characterize the microstructure of RS ribbons.The results show that there is high density of particles distributed within grains and at grain boundaries in the region near wheel side.The particle density is decreased in the middle region and free surface region.The alloy is predominantly composed of supersaturated--Mg solid solution,T phase and W phase;meanwhile,a few icosahedral quasicrystalline and Mg4Zn7 particles are also observed.The T phase is confirmed having a body-centered orthorhombic structure that is transformed from the body-centered tetragonal structure Mg12Ce phase due to the partial substitution of Mg atoms by Zn.

热作用对喷射沉积Mg-7Al-1.5Zn-4.5Ca-1Nd合金坯组织的影响

采用喷射沉积方法制备了Mg-7Al-1.5Zn-4.5Ca-1Nd合金,通过对沉积态合金不同温度加热处理后试样的组织观察,分析了此合金的相变及组织演变特征。结果表明:喷射沉积坯晶粒细小,组织分布均匀,组织中含有α-Mg、Mg17Al12、MgZn2、Al2Ca和Ca2Mg6Zn3等相;当加热温度从350℃升到520℃时,喷射沉积坯组织有明显的变化,Mg17Al12相溶解,Ca2Mg6Zn3分解为Mg2Ca和MgZn2相,高温时析出了新相Mg12Nd;且硬度随着加热温度的升高而持续下降。

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.

生物合金Mg-4Zn-1Ca合金在SBF模拟体液中腐蚀性能的研究

采用真空气氛保护金属型制备Mg-4Zn-1Ca三元合金，利用光学显微镜、扫描电子显微镜、浸泡腐蚀失重试验研究了铸态Mg-4Zn-1Ca合金在SBF模拟体液中的腐蚀行为及腐蚀性能。结果表明，Mg-4Zn-1Ca合金的腐蚀速率随着时间的延长而降低，并观察到在60min时氧化膜丧失保护能力。经过5h浸泡后，铸态合金的平均腐蚀速率从最高的10．91mm／a下降到了4．447mm／a。