镁合金AZ91HP强流脉冲电子束表面处理及抗蚀性能研究

研究了强流脉冲电子束表面处理对镁合金AZ91HP腐蚀性能的影响。通过动电位极化曲线测定，处理样品在5％NaCl溶液中的抗蚀性能有显著改善。72h盐浸失重法测试中，处理样品的腐蚀速度最大可以降低一个数量级。扫描电镜(SEM)及电子探针(EPMA)分析发现，强流脉冲电子束轰击处理在AZ91HP样品表层引发快速熔凝过程，进而导致镁、铝元素的含量及分布形式发生变化。样品表面重熔层中Al元素的过饱和固溶及成分均匀化是改善其腐蚀性能的主要原因。     

Improved Corrosion Resistance of Magnesium Alloys AZ31 and AZ91HP by High Current Pulsed Electron Beam Treatment

MAGNESIUM ALLOYS are now receiving more andmore applications in the electronic communication,aeronautic and automotive products due to their lowdensity,high strength to weight ratio and goodcastability[1-3]-However,the inherently poorcorrosion resistance of magnesium alloys limits theirfurther utilization.Therefore,significant efforts havebeing made to find one way that allows improving thecorrosion resistance of magnesium alloys effectively.Increasing the purity of magnesium alloy and t…     

纯镁和镁合金强流脉冲电子束表面合金化性能

利用强流脉冲电子束对纯镁及镁合金AZ31和AZ91HP进行表面合金化处理。用光学显微镜和扫描电镜对表面处理层形貌和组织进行了分析,腐蚀性能和摩擦磨损测试表明:纯镁表面合金化铝后,样品抗5%NaCl溶液腐蚀性能得到显著提高,维钝电流降低2个数量级以上;而镁合金AZ31以及AZ91HP表面合金化Cr、TiN后,耐磨性均得到提高。     

Improvement of Wear Resistance of Magnesium Alloy AZ91HP by High Current Pulsed Electron Beam Treatment

MAGNESIUM ALLOYS exhibit high strength toweight ratio and stiffness and are finding theirapplications in air,automobile and electronic industries.Despite the worldwide growing interests inmagnesium alloys,their inferior wear resistance is aserious impediment.Considering that wear is asurface-related behavior,surface modification canresolve the problem.Recently,intense and pulsed energetic beams areemerging as new and effective methods for surfacemodification.The High Current Pulsed Ele…     

Improvement of wear resistance of AZ31 and AZ91HP by high current pulsed electron beam treatment

The surface modification of magnesium alloys （AZ31 and AZ91 HP） was studied by a high current pulsed electron beam（HCPEB）. The results show that the cross-sectional microhardness of treated samples increases not only in the heat affected zone（ HAZ）, but also beyond HAZ, reaching over 250μm. This is due to the action of quasi-static thermal stress and the shock thermal stress wave with materials, which result in its fast deformation on the surface layer and so increases microhardness. For the AZ91HP alloy, a nearly complete dissolution of the intermetallic phase Mg17Al12 is observed, and a super-saturated solid solution forms on the re-melted surface, which is due to the solute trapping effect during the fast solidification process. Measurements on sliding wear show that wear resistance is improved by approximately 5.6 and 2.4 times for the AZ31 and AZ91HP respectively, as compared with as-received samples.     

铝基非晶纳米晶复合涂层研究

采用自动化高速电弧喷涂系统,用自行研制的粉芯丝材,在AZ91镁合金基体表面上制备出Al-Ni-Y-Co非晶纳米晶复合涂层.采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、透射电子显微镜(TEM)分析了Al-Ni-Y-Co非晶纳米晶复合涂层的微观形貌和组织结构,结果表明Al-Ni-Y-Co非晶纳米晶复合涂层是由非晶相和纳米晶化相共同组成的,涂层结构致密,孔隙率约为1.8%.Al-Ni-Y-Co非晶纳米晶复合涂层的平均显微Vickers硬度值为311.7 HV0 1,结合强度为26.8 MPa.涂层的抗磨损耐腐蚀性能优于Al涂层和AZ91镁合金基体;其相对耐磨性约为Al涂层的10倍,为AZ91镁合金的6倍;其自腐蚀电位值正于Al涂层及AZ91镁合金,自腐蚀电流密度值约为Al涂层的1/2,AZ91镁合金的1/5;其腐蚀后的表面形貌比Al涂层和AZ91镁合金平整,点蚀较少.Al-Ni-Y-Co非晶纳米晶复合涂层的耐磨防腐综合性能优异.     

Characterization of plasma electrolytic oxide formed on AZ91 Mg alloy in KMnO4 electrolyte

The aim of this work is to investigate microstructure, corrosion resistance characteristics and nanohardness of the oxide layer on AZ91 Mg alloy by applying different voltage with KMnO₄ contained solution. There are lots of closed pores that are filled with another oxide compound compared with the typical surface morphology with pore coated until 350 V of coating voltage. The thickness of oxide layer increases with increasing coating voltage. The oxide layer formed on AZ91 Mg alloy in electrolyte with potassium permanganate consists of MgO and Mn₂O₃. Corrosion potential of the oxide layer on AZ91 Mg alloy obtained at different plasma electrolytic oxidation(PEO) reaction stages increases with increasing coating voltage. The corrosion resistance of AZ91 Mg alloy depends on the existence of the manganese oxide in the oxide layer. The inner barrier layer composed of the MgO and Mn₂O₃ may serve as diffusion barrier to enhance the corrosion resistance and may partially explain the excellent anti-corrosion performance in corrosion test. Nanohardness values increase with increasing coating voltage. The increase in the nanohardness may be due to the effect of manganese oxide in the oxide layer on AZ91 Mg alloy coated from electrolyte containing KMnO₄.     

强流脉冲电子束表面改性AZ31镁合金的耐磨耐蚀性能

选用强流脉冲电子束对AZ31镁合金进行表面改性处理,分析了改性后的AZ31镁合金表面显微结构,测量处理前后AZ31镁合金的耐磨性能和耐蚀性能。结果表明,脉冲电子束处理后AZ31合金表面出现了典型的熔坑形貌,同时熔坑周围有应力波作用产生的褶痕。由电子束快速凝固作用所产生的表层晶粒细化和固溶强化显著提高了AZ31合金的耐磨性。此外,电子束表面改性导致表层镁、铝元素含量及分布形式发生变化。样品表层铝元素的升高是改善其腐蚀性能的主要原因。     

Effect of Hydrogen on Corrosion and Stress Corrosion Cracking of AZ91 Alloy in Aqueous Solutions

The effect of hydrogen on the corrosion and stress corrosion cracking of the magnesium AZ91 alloy has been investigated in aqueous solutions.Hydrogen produced by corrosion in water diffuses into,and reacts with the Mg matrix to form hydride.Some of the hydrogen accumulates at hydride/Mg matrix(or secondary phase) interfaces as a consequence of slow hydride formation and the incompatibility of the hydride with the Mg matrix(or secondary phase),and combines to form molecular hydrogen.This leads to the development of a local pressure at the hydride/Mg matrix(or secondary phase)interface.The expansion stress caused by hydride formation and the local hydrogen pressure due to its accumulation result in brittle fracture of hydride.These two combined effects promote both the corrosion rate of the AZ91 alloy,and crack initiation and propagation even in the absence of an external load.Hydrogen absorption leads to a dramatic deterioration in the mechanical properties of the AZ91 alloy,indicating that hydrogen embrittlement is responsible for transgulanar stress corrosion cracking in aqueous solutions.     

微弧表面处理对AZ31B镁合金耐腐蚀及耐腐蚀疲劳性能的影响

采用微弧表面处理技术(微弧氧化MAO和微弧复合MCC)在AZ31B镁合金基体上制备出不同断面结构的防护涂层。通过电化学腐蚀及腐蚀疲劳测试方法,研究了MAO、MCC涂层的电化学腐蚀及腐蚀疲劳性能。结果表明,生长10 min的MAO涂层具有较好的耐电化学腐蚀性能。MAO涂层表面存在微孔和微裂纹,在应力条件下微孔和微裂纹作为疲劳断裂的裂纹萌生点,可加速裂纹的萌生与扩展,使其腐蚀疲劳寿命相较AZ31B合金基体降低了55%。而具有MCC涂层的AZ31B合金试样腐蚀疲劳极限为(64.0±5.4) MPa,比AZ31B合金基体提高了59%。在低应力载荷下(＜80 MPa),微弧复合涂层试样的腐蚀疲劳强度得到明显提高。     

AZ31镁合金表面强流脉冲电子束铝合金化研究

利用强流脉冲电子束对AZ31镁合金表面进行快速铝合金化,分析了表面合金化层的显微结构,测量了铝合金化前后,AZ31镁合金的腐蚀性能与耐磨性能.结果表明,经电子束轰击后表层出现了典型的熔坑形貌;耐磨性能测试表明,加速电压为27 kV,脉冲5次的试样比原始试样的相对耐磨性提高6倍,同时合金化也提高了在5%的NaCl溶液中的耐腐蚀性能.     

AZ91D镁合金微弧氧化膜的腐蚀行为研究

利用双向全波脉冲电源对AZ91D镁合金在硅酸盐体系中进行了微弧氧化处理,通过电化学阻抗谱(EIS)测试、极化曲线分析并结合XRD和SEM等分析方法对微弧氧化处理的镁合金腐蚀行为进行了研究.结果表明,微弧氧化膜表面分布着几微米的微孔,微弧氧化膜中主要含有MgF2,Mg2SiO4和Al2O3.AZ91D镁合金经过微弧氧化处理之后,耐蚀性能明显提高,自腐蚀电流密度降低3个数量级,自腐蚀电位高出约300 mV,阻抗值高出3个数量级,研制的微弧氧化膜对镁合金具有很好的防腐保护性能.     

SiCw/AZ91镁基复合材料的微弧氧化行为及涂层的耐腐蚀性能

采用微弧氧化表面处理技术在SiCw/AZ91镁基复合材料表面制备保护性涂层.通过与AZ91镁合金对比,研究镁基复合材料的微弧氧化行为及其形貌特征,并采用电化学方法评价了微弧氧化涂层的耐腐蚀性能.结果表明,SiC晶须的存在影响了基底材料表面阻挡层的形成,使复合材料的微弧氧化行为不同于基体合金.与合金相比,在恒电流模式下进行微弧氧化的过程中复合材料的电压随时间的演变趋势不够理想,而且在相同工艺条件下复合材料的起弧时间比合金要长.复合材料在微弧氧化过程中偶尔会出现烧蚀现象.虽然SiC晶须会影响复合材料表面涂层的形成,微弧氧化处理仍然能够增强镁基复合材料的耐腐蚀性能,使其自腐蚀电位提高,腐蚀电流降低.当采用恒压模式制备涂层时,涂层耐腐蚀性能随电压的提高而增强.     

压铸镁合金AZ91D在酸性NaCl溶液中的腐蚀行为

采用电化学方法研究了压铸镁合金AZ91D在酸性NaCl溶液中的腐蚀行为,并用扫描电镜观察了腐蚀形貌,对腐蚀产物进行了能谱分析.研究结果表明:在酸性溶液环境下,随着Cl-浓度的升高,镁合金的平衡腐蚀电位降低,线性阻抗减小,腐蚀电流增大;随着pH值的减小,晶界出现腐蚀开裂现象;富Al相的耐蚀性高于基体相,在酸性环境中,腐蚀产物主要为MgO和Mg(OH)2     

AZ91D镁合金微弧氧化工艺参数的优化

利用自制微弧氧化装置在硅酸盐体系中对AZ91D镁合金进行微弧氧化处理.采用4因素3水平正交试验,从考察膜层厚度、表面粗糙度和耐蚀性出发,确定了AZ91D镁合金在硅酸盐体系中的最佳工艺参数.结果表明：在最佳工艺条件下,微弧氧化膜呈多孔结构、孔径较小,裂纹较少,分布均匀,膜层较为致密;微弧氧化膜由MgO、Mg2SiO4、MgAl2O4和少量的SiO2组成;室温下,在质量分数为3.5%的NaCl中性溶液中浸泡168 h后,膜层表面未出现明显的点蚀现象,耐蚀性较镁合金基体有了很大提高.     

Effect of excimer laser surface melting on the microstructure and corrosion performance of the die cast AZ91D magnesium alloy

Excimer laser surface melting (LSM) of the die cast AZ91D alloy has been investigated in terms of microstructure and corrosion behaviour. Excimer LSM of the alloy resulted in a highly homogeneous and refined melted microstructure, which improved the corrosion resistance of the alloy. The latter was associated with the large dissolution of intermetallic phases and the enrichment of aluminium within the melted layer. An increased number of laser pulses resulted in thicker melted layers, but also in enhanced porosity and the formation of micro-cracks at the overlapping area. Both factors diminished the corrosion resistance of the laser-treated alloy.     

Corrosion resistance of Mg–8·8Li alloy compared with AZ91

Abstract

The superlight Mg–Li alloys exhibit good formability but poor corrosion resistance due to the alloying of lithium. In this paper, the corrosion behaviour of Mg–8·8Li alloy was investigated by electrochemical measurements, corrosion morphology observations and weight loss determination. The results indicate that Mg–8·8Li alloy displays worse corrosion resistance than AZ91D alloy in the early stages of corrosion. However, the corrosion resistance of AZ91D alloy declines and becomes worse than Mg–8·8Li alloy with increasing exposure time. In addition, it is found that a 250°C annealing treatment has a detrimental effect on the corrosion resistance of Mg–8·8Li alloy.     

AZ91镁合金表面电化学沉积羟基磷灰石涂层的制备及其耐蚀性

采用电化学沉积方法在AZ91镁合金表面制备了羟基磷灰石(HA)涂层,研究了电沉积工艺参数对羟基磷灰石涂层形貌和相组成的影响,并通过腐蚀浸泡试验、极化曲线测试等方法对该涂层的耐蚀性进行了研究。结果表明:当溶液pH为4.5,温度为60℃时,涂层的致密性最好,呈放射状的结构,主要成分为HA相,涂层的厚度约为60~70μm,与基体结合较好;HA涂层对镁合金基体具有较好的保护作用,显著提高了基体合金在生理溶液中的耐蚀性。     

热处理对AZ91D镁合金腐蚀性能的影响

对经过不同热处理工艺处理后的AZ91D镁合金进行腐蚀试验,并测定其腐蚀参数.对腐蚀数据及金相显微组织分析、观察表明:时效处理后的AZ91D镁合金腐蚀率最低为2.128mm/a,为铸态和固溶加时效处理的AZ91D镁合金(3.081mm/a、3.209mm/a)的69.1%和66.3%;比仅进行固溶处理的AZ91D镁合金7.400mm/a的腐蚀率减少了71.2%,耐蚀性能提高2.48倍.合金组织中β相的形态和数量对合金腐蚀率起着重要作用.     

Effects of Mn on Corrosion Resistant Property of AZ91 Alloys

采用电化学、静态失重、盐雾腐蚀法研究了Mn对热处理态AZ91合金耐蚀性能的影响,利用扫描电镜观察试样的微观形貌,用X射线衍射仪分析合金的物相组成和腐蚀产物。结果表明,Mn与AZ91合金中的Al形成了独立相Al6Mn,该相溶解到Mg固溶体中提高了Mg的电极电位,进而提高了合金的耐腐蚀性;Mn加入后使合金的自腐蚀电位升高,自腐蚀电流密度降低,降低了合金的腐蚀速率,进而提高了合金的耐腐蚀性能,且三种实验方法都表明AZ91-0.8Mn合金的耐腐蚀性能最好。