AZ31镁合金表面钼酸盐转化膜的制备与耐蚀性能

以Na2Mo O4为主盐,与氧化剂H2O2、成膜促进剂NaF和Na2Si O3一起组成化学转化液,在AZ31镁合金表面制备钼酸盐转化膜,利用扫描电镜和X线光电子能谱仪分析转化膜的形貌和组成,通过电化学阻抗测试研究转化膜在3.5%Na Cl溶液中的腐蚀行为,并讨论成膜机理,研究转化液中Na2Mo O4浓度与p H以及成膜温度和时间对薄膜结构与耐腐蚀性能的影响。结果表明:转化液的优化组成为0.2 mol/L Na2Mo O4+0.12 mol/L NaF+0.014mol/L Na2Si O3+0.012 mol/L H2O2;优化工艺条件为p H=5,温度60℃,转化时间30 min;转化膜为黄棕色,主要由Mg Mo O4,Mg F2,Mo O2,Mo O3和Mg Si O3组成,转化膜宏观上完整均匀,存在网状微裂纹;钼酸盐转化膜能有效提高AZ31镁合金的耐腐蚀性能,对基体合金有一定的保护作用。     

Effect of cerium and lanthanum additives on plasma electrolytic oxidation of AZ31 magnesium alloy

Plasma electrolytic oxidation（PEO） coatings on AZ31 magnesium（Mg） alloy were developed using the aqueous solution with alkaline silicate and sodium hydroxide as a base electrolyte system.The effects of cerium（Ce） nitrate and lanthanum（La） nitrate additives on the voltage response,microstructure,compositions and corrosion resistance of PEO coatings were investigated by scanning electron microscopy（SEM）,energy-dispersive spectrum（EDS）,X-ray diffraction（XRD） and potentiodynamic polarization tests,etc.The results showed that Ce and La additives increased the stable voltage and compactness of the PEO coatings,while,those did not change the compositions of the PEO coatings.The corrosion resistance of the PEO coating obtained in solutions with La nitrate of 0.1 g/L was the best,followed by that with Ce nitrate of 0.1 g/L and that without additives.     

AZ31镁合金微区电偶腐蚀的数值研究

结合水平集函数方法及移动网格技术,利用有限元法模拟分析了离散型β相分布和连续型β相分布的AZ31镁合金在NaCl溶液中的腐蚀行为,通过解Nernst-Planck方程得到腐蚀过程中AZ31镁合金/NaCl界面的电势、氯离子及镁离子浓度分布,并通过扫描离子选择性电极实验验证了此模拟方法的可行性.模拟分析表明,当β相离散分布在α相周边时,在与β相相邻的α相区域腐蚀速率最快,形成腐蚀缩颈坑,坑内氯离子富集,进一步加速了α相的腐蚀,最终β相逐渐脱离合金进入溶液;当β相连续分布在α相周边时,α相不断被腐蚀,最终α相全部溶解而只剩β相,求解随即停止.扫描离子选择性电极实验结果表明此模拟模型可以对镁合金的电化学腐蚀进行较好预测和判断.     

Effect of samarium on microstructure and corrosion resistance of aged as-cast AZ92 magnesium alloy

The effects of samarium（Sm） on microstructure and corrosion resistance of AZ92 magnesium alloy were characterized and analyzed by scanning electronic microscopy, X-ray diffraction, mass loss test, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy and potentio-dynamic polarization test. The results showed that the added Sm could promote continuous precipitation of β-Mg17Al12 phase in grains, and meanwhile restrain discontinuous precipitation of the same phase along the grain boundaries. Thus, the precipitations distributed more uniformly in the aged AZ92 magnesium alloys. When the content of Sm was 0.5 wt.%, the corrosion resistance of aged AZ92 alloy tended to be the best, which was due to the β-phase distributes more homogeneous reducing the galvanic corrosion. The corrosion product film had more integrality and compactness than AZ92 alloys without Sm. However, it resulted in worse corrosion resistance of AZ92 alloy because of the formation of mass cathodic Al2 Sm phase coming from excess Sm in AZ92 alloy.     

Stress corrosion cracking behaviors of RE-containing ME21 magnesium alloy processed by equal-channel angular pressing

A commercial as-cast ME21 magnesium alloy containing rare-earth (RE) element was processed by equalchannel angular pressing to obtain fine-grained micro structure. Stress corrosion cracking (SCC) behaviors of the fine-grained samples were studied by slow-strain-rate testing in air, distilled water and Hanks’solution at the strain rate of 1×10~(-6) s~(-1). All samples show a relatively low SCC sensitivity in distilled water but a great SCC tendency in Hanks’ solution. The microscopic observations of the fracture surfaces and the side surfaces reveal obvious active anodic dissolution and hydrogen embrittlement cracks, which indicate the higher SCC susceptibility in Hanks'solution. The fine-grained microstructure with more crystal defects promotes the passivation process of the oxide film and restrains the hydrogen induced cracking of the ME21 magnesium alloy, leading to the higher general corrosion resistance as well as SCC resistance.     

Effect of surface preparation on the corrosion resistance of friction stir linear lap welded AZ31B-H24

The effect of surface preparations on the atmospheric (continuous NaCl salt fog) corrosion resistance of bare (uncoated) linear friction stir lap welded magnesium (Mg) alloy AZ31B-H24 joints was investigated. The surface preparations evaluated included as-received (as-welded for the weld zones), mechanically abraded and acid-cleaned. Electrochemical potentiodynamic polarisation, X-ray photoelectron spectroscopy and Auger electron spectroscopy measurements were made to elucidate the link between the surface preparation and the relative corrosion resistance observed across the microstructural zones of the joints. Heavy metal surface contamination of the as-received material, rather than the air-formed oxide or differences in alloy grain size resulting from variations in thermo-mechanical processing history, was found to be the controlling factor affecting the corrosion mode observed and, in turn, the relative corrosion resistance across the joint. Removal of the heavy metal contamination changed the corrosion mode from pit-like to filament-like, which in turn homogenised the corrosion resistance across the joint in the continuous salt fog exposure.     

含氯离子环境下锌铝伪合金涂层的耐蚀性及电化学特性

采用盐雾试验和电化学阻抗谱测试技术研究了纯锌和锌铝伪合金涂层在含氯离子环境中的腐蚀行为和电化学特性,通过扫描电镜、X射线物相分析等手段研究了原始涂层及腐蚀后的表面形貌和腐蚀产物的相结构,并对两种涂层的腐蚀机理进行了初步的探讨.随着盐雾时间的增加,纯锌涂层表面逐渐生成疏松多孔的胞状腐蚀产物层,主要腐蚀产物为Zn₅(OH)₈Cl₂H₂O、ZnO和Zn₅(CO₃)₂(OH)₆,盐雾试验达到768 h后腐蚀产物层局部区域发生龟裂.锌铝伪合金涂层表面生成致密的腐蚀产物层,主要为Zn₅(OH)₈Cl₂H₂O、Zn_0.71Al_0.29(OH)₂(CO₃)_0.145·xH₂O及ZnAl₂O₄.电化学阻抗谱测试结果表明:随着盐雾时间的延长,两种涂层的电荷转移电阻均逐渐增大,但锌铝伪合金涂层的阻抗要明显大于纯锌涂层,表现出了更好的耐蚀性.     

小电流镀铜对阳极氧化AZ31镁合金耐蚀性的影响

研究了小电流镀铜封孔对阳极氧化AZ31镁合金耐蚀性能的影响.AZ31镁合金阳极氧化后,在传统的镀铜液中进行阴极小电流处理.SEM、EDS和XRD分析结果表明,阴极小电流处理后,在阳极氧化膜的多孔层中发生了铜的沉积.在质量分数为3.5%NaCl水溶液中测试的极化曲线表明,AZ31镁合金阳极氧化后进行小电流镀铜处理,可以提高自腐蚀电位,降低自腐蚀电流密度,使耐蚀性能得到显著提高.     

变形参数对AZ31镁合金变形抗力的影响

利用Gleeble-1500热模拟试验机对AZ31镁合金在变形温度为250~400℃、变形速率为0.5~3.0s^-1下进行热变形模拟实验,得到了AZ31镁合金真实应力-真实应变曲线,并通过光学显微镜观察了试样在变形中的微观组织.结果表明,动态再结晶是该实验条件下晶粒细化的主要机制,变形参数影响了再结晶的程度.     

镁合金AZ31动态再结晶行为的取向成像分析

利用背散射电子衍射(EBSD)取向成像技术分析了具有不同初始织构的镁合金AZ31动态再结晶晶粒的取向特征以及与相邻的形变晶粒的取向关系.结果表明:不同初始织构以及不同应变量下动态再结晶新晶粒与形变晶粒的取向都相近,说明动态再结晶以连续方式进行,即亚晶转动方式.随形变量的增加,不同初始织构试样的晶粒都转向基面取向,但菊池带衬度图像显示大的形变晶粒内部很少有亚晶界存在并且菊池带质量高,说明塑性滑移机制仍在起很大作用但在靠近晶界处发生,形变晶粒是通过平行于压缩面方向剪切晶界而逐渐消失的.动态再结晶晶粒与相邻形变晶粒的取向差表明不同初始织构造成不同的取向差,但总的趋势是相同的.     

Study on solid solution and aging process of AZ91D magnesium alloy with cerium

The influence of Ce on solid solution and aging process of AZ91D magnesium alloy was analyzed.The results showed that the decomposition of β-Mg17Al12 phase in AZ91D magnesium alloy at 420 ℃ could be completed within 12 h,while this process in the Ce-containing alloy required more time.In subsequent aging process at 175 ℃,Ce obviously delayed the aging process of AZglD.It was inferred that the influence of Ce on process of solid solution and aging was relative to the Ce that existed in β-Mg17Al12 phase of original structure in the form of solid solution,and the interaction of the Ce and Al was an important factor to get process of solution and aging slowly.     

稀土Nd对AZ 31镁合金铸态组织和力学性能的影响

利用气氛电阻炉制备了AZ 31-xNd合金(x=0.05%,0.1%,0.2%,0.4%,0.6%),采用光学显微镜(OM)、扫描电子显微镜(SEM)和电子能谱分析仪(EDS)对不同Nd含量的实验合金进行了显微组织观察和分析,结果发现,Nd在AZ 31-xNd合金中形成了Al_3Nd和Mg_(12)Nd相,这些含Nd相导致AZ 31镁合金在凝固过程中的晶粒细化,从而提高了AZ 31镁合金的铸态室温力学性能,随着Nd含量的增加,合金的铸态室温抗拉强度极限和延伸率均先升高后降低.     

近液相线半连续铸造AZ91D镁合金微观组织研究

用近液相线半连续铸造法制备出具有球状和蔷薇状晶粒的AZ91D合金坯料。考察了铸造速度对合金微观组织的影响，以及对铸锭边部和中心组织差异的影响。实验结果表明，随铸造速度的增加，铸锭逐渐趋向枝晶化，边部和中心组织差异经历了由小到大，再由大到小的变化。并对铸造速度的影响机理进行了分析。     

海水温度对深海用环氧涂层防护性能的影响

采用电化学阻抗谱(EIS)技术,研究了环氧重防腐涂层在不同温度海水中的腐蚀电化学行为.结果表明,随着海水温度的升高,涂层体系的涂层电容值的升高和涂层电阻值的降低均加快,说明海水温度的升高,加速了涂层防护性能的下降,加快了基体金属的腐蚀.浸泡初期,在不同温度的海水中,水在涂层中的扩散均符合Fick扩散第二定律,扩散活化能为49.7kJ·mol^-1.随着海水温度的升高,涂层中水的扩散系数增大,涂层吸水达到饱和的时间缩短,但饱和吸水量变化不大.     

Effects of precipitates on grain size and mechanical properties of AZ31-x% Nd magnesium alloy

The effects of precipitates on grain size and mechanical properties of as-cast AZ3 1-x%Nd magnesium alloy were investi- gated, and the affecting mechanism was also discussed. The results indicated that Al2Nd phase, AlllNd3 phase and a few AI-Mn-Nd-Fe phase were furmed when adding 0.38 wt.%-1.46 wt.% Nd into AZ31 melt, coarse AI2Nd transformed into Al11Nd3 gradually with the increasing of Nd content. Due to structure and size transformation and content increasing of AI-Nd phase, the grain size of AZ31-x% Nd alloy increased firstly, and then decreased with the increment of Nd content. After reaching a minimum value, once again it rose up, provided that Nd content was further increased. The tensile property reached its optimal value when the adding amount of Nd content was 1.05 wl.%, however, adding excessive amount of Nd deteriorated both ultimate strength and elongation ofAZ31 alloy.     

AZ31镁合金细管静液挤压工艺及组织性能分析

镁合金由于良好的生物相容性、可降解性和优良的力学性能,而展现出在医疗器械应用上的优越性.以AZ31镁合金为研究对象,研究镁合金细管静液挤压成形新技术,并且开发出一种高强韧AZ31镁合金薄壁细管.结果表明:模具预热温度为300℃,挤压坯料温度200℃,挤压比为17 ～31.5,采用超细石墨-PVC塑料粉制备的静液挤压用传力润滑介质进行静液挤压,获得的细管综合性能最好;挤压管坯组织与挤压前相比,得到明显改善,挤压前平均晶粒粒径为150μm,挤压后平均晶粒粒径＜7.0μm;抗压强度由均匀化处理后的210.5MPa提高至挤压后的375.2MPa.     

非对称轧制对AZ31B镁合金组织及性能的影响

开展了非对称轧制对AZ31B镁合金晶粒细化影响的研究,分析了不同温度及不同压下率时宏观形貌和晶粒尺寸变化,并与对称轧制作了对比。结果表明,非对称轧制的整体晶粒尺寸比对称轧制更为细化;非对称轧制在温度为350 ℃、压下率为60%时晶粒最为细小均匀,上表面、中心层和下表面的平均晶粒尺寸分别为2.35、2.84和2.22 μm。在初轧温度为300～350 ℃范围内,组织产生充分动态再结晶;随着轧制温度继续升高,晶界产生充分迁移和扩散,晶粒随之长大,导致镁合金的综合性能变差。非对称轧制板材的抗拉强度和断后伸长率都优于对称轧制板材,在400 ℃轧制时,压下率为30%时获得较为优异的综合力学性能,抗拉强度为365.36 MPa,断后伸长率为34.9%。     

Microstructure and mechanical properties of friction stir welding of AZ31B magnesium alloy added with cerium

The AZ31B magnesium alloy sheet added with 0.5 wt.% Ce was welded with friction stir welding(FSW).The microstructures and mechanical properties of the welded joint were investigated.The results showed that the microstructures in the weld nugget zone were uniform and with small equiaxed grains.The grains in the heat-affected zone and the thermo-mechanical affected zone were coarser than those in the base metal zone and the weld nugget zone.The ultimate tensile strength of AZ31B magnesium alloy added with 0.5...     

EBSD探究脉冲电流作用对AZ31镁合金微观结构的影响

借助扫描电子显微镜中电子背散射衍射技术探究了脉冲电流作用次数对样品内部晶粒取向的影响,通过对不同样品微取向差分布的统计系统研究了脉冲电流作用次数对AZ31镁合金微观结构的影响.研究结果表明,脉冲电流作用过程中晶粒发生转动,尤其随作用次数增加,晶粒尺寸分布变得更加均匀.晶粒取向差图分析可知,脉冲电流作用后随作用次数的增加,样品中大角度取向差的晶粒增多,同时伴随着拉伸孪晶增多.     

Influence of neodymium on high cycle fatigue behavior of die cast AZ91D magnesium alloy

High cycle fatigue behavior of die cast AZ91D magnesium alloy with different Nd contents was investigated.Axial mechanical fatigue tests were conducted at the stress ratio R=0.1 and the fatigue strength was evaluated using up-to-down load method on specimens of AZ91D with different Nd contents.The results showed that the grain of AZ91D alloy was refined,the size and amount of β-Mg17Al12 phase decreased and distributed uniformly with increasing Nd content.At the number of cycles to failure,Nf=107,the fatigue...