AZ31镁合金微弧-电泳复合膜层制备工艺及其耐蚀性

基于镁合金弧氧化陶瓷层的截面与表面形貌特征,设计了微弧-电泳复合处理工艺,并简化了电泳工艺.耐酸、耐碱实验表明:在酸性腐蚀条件下,镁合金微弧氧化陶瓷层在1min内已被破坏,而微弧电泳复合膜层在65min后才开始破坏,且耐酸性随微弧氧化时间的延长而增强,在微弧氧化8min~12min后施行电泳,所得复合膜层可耐酸130min.在碱性条件下腐蚀7d,两种膜层表面无腐蚀迹象.     

AZ91镁合金表面微弧氧化与化学镀铜复合处理层的微观组织与性能

采用微弧氧化技术在AZ91镁合金表面制备Mg O陶瓷膜层,然后在该膜层通过化学镀铜技术制备金属铜层。利用SEM,XRD,EDS,电化学实验及四探针测试等手段研究了复合膜层的显微结构、相组成、耐蚀性和导电性。结果表明:微弧氧化处理获得以Mg O为主相的陶瓷层可有效提高镁合金的耐蚀性,平均厚度为2.5μm的化学镀铜层连续均匀地覆盖在微弧氧化陶瓷层表面,渗入并填充微弧氧化陶瓷层内部呈网状分布的孔隙,形成交错咬合状态;复合膜层表面的导电性良好,与基体镁合金相比,复合膜层的腐蚀电位提高了0.2 V,腐蚀电流密度下降了一个数量级。但由于化学镀铜层与基体镁合金之间产生的电偶腐蚀,导致复合膜层的耐蚀性较陶瓷层有所下降。     

镁合金微弧氧化-电泳复合膜层的腐蚀性能

镁合金微弧氧化-电泳复合处理作为新型的表面处理工艺,极大地提高了镁合金的耐蚀性,满足了工业化要求。通过考察在不同工艺条件下制备镁合金微弧氧化-电泳复合膜层的耐蚀性,研究其腐蚀机理,结果表明:微弧氧化-电泳复合膜层的耐蚀性取决于有机层的致密性以及复合膜层间的结合状态。致密性越好、结合力越大,复合膜层的耐蚀性越好。     

AZ91镁合金表面微弧氧化与磁控溅射镀铜复合处理层的微观组织与性能

采用微弧氧化技术在AZ91镁合金表面制备陶瓷涂层,然后在该涂层表面通过磁控溅射镀铜技术制备复合膜层。研究了微弧氧化陶瓷层和复合膜层的表面物相组成、表面粗糙度、表面及截面形貌、表面润湿性及电化学性能。结果表明:AZ91镁合金经微弧氧化处理后由于微弧氧化陶瓷层呈微纳粗糙多孔结构,表现为亲水特性,其物相由MgO、Mg及Mg_2SiO_4组成;而微弧氧化陶瓷层经磁控溅射镀铜处理后表面获得较为致密的具有疏水特性的铜层,表面粗糙度降低;四探针测试结果说明复合膜层的方阻为16.2 m?·~(-1),导电性良好;动电位极化曲线测试结果说明复合膜层与基体镁合金相比,其腐蚀电流密度降低10%,腐蚀电位提高了约0.36 V,腐蚀极化电阻提高约80倍;与微弧氧化陶瓷层相比,复合膜层的腐蚀电位提高了约0.24 V,但其腐蚀电流密度和腐蚀极化电阻有所下降。研究结果表明,微弧氧化与磁控溅射镀铜相结合的复合处理技术可在不降低镁合金陶瓷层耐蚀性的基础上显著提高其表面的导电性能。     

镁合金微弧氧化陶瓷层表面的电泳成膜机理

研究镁合金微弧氧化(PEO)陶瓷层表面的电泳成膜机理;分析工艺参数对复合膜层耐蚀性的影响.采用扫描电镜、示波器和盐雾试验机等分别研究复合膜层的表面和截面形貌、电泳过程中电流变化规律及腐蚀防护性能.结果表明:在电泳成膜过程中,微弧氧化陶瓷层微孔处被击穿,电泳回路产生电流,电泳漆带电粒子先在微孔处沉积,然后向周围移动并沉积,当电流降为0时,电泳过程结束.随着陶瓷层厚度和粗糙度的增加,陶瓷层被击穿时间延长,电泳漆粒子沉积时间缩短.微弧氧化陶瓷层的腐蚀速率是微弧氧化/电泳涂装复合膜层的6.286倍,说明镁合金微弧氧化陶瓷层经电泳处理后,其耐蚀性得到了显著的增强.     

Mg-Mn-Ce镁合金表面超疏水复合膜层的制备及耐腐蚀性能

采用微弧氧化技术和有机镀膜技术相结合的复合处理方法实现Mg-Mn-Ce镁合金表面改性,获得超疏水复合膜层,研究微弧氧化膜的表面特征、有机镀膜电化学反应过程、复合膜层的润湿特性和耐腐蚀性能。结果表明:镁合金经微弧氧化处理后由于微弧氧化膜表面呈微纳多孔结构,表现为超亲水特性,其蒸馏水的静态接触角接近0°;在微弧氧化膜上经有机镀膜后,其形成的有机薄膜的静态接触角高达173.3°,表现出优良的超疏水特性。镁合金经微弧氧化处理后具有良好的耐腐蚀性能,经有机镀膜超疏水复合处理后,耐腐蚀性能得到进一步提高。复合膜层在3.5%NaCl溶液中,与基体相比动电位极化腐蚀电流密度减小了3个数量级、而电化学阻抗提高了3个数量级,耐腐蚀性能明显改善。微弧氧化与有机镀膜相结合的复合处理使镁合金表面在实现超亲水-超疏水功能转换的同时显著提高镁合金的耐腐蚀性能。     

镁合金微弧氧化膜有机封孔耐腐蚀性能的研究

镁合金AZ91D经微弧氧化处理后得到与基体结合牢固、表面多孔的氧化膜,研究了在该氧化膜上涂覆有机涂层进行封孔的方法,利用扫描电镜从复合膜层的横截面分析了有机涂层对微弧氧化膜层的封孔情况,并对封孔后的镁合金表面膜层的结合性能和耐腐蚀性能进行了初步试验分析.研究表明,有机涂层能渗入微弧氧化膜孔洞内5～30μm,与氧化膜层结合紧密.经1% HCl溶液浸泡试验,结果表明经过有机封孔后的微弧氧化膜层的耐腐蚀性能大大提高.     

AZ31B镁合金表面微弧氧化-溶胶凝胶复合膜层干、湿热交替条件下耐蚀性研究

采用微弧氧化与溶胶凝胶技术在AZ31B镁合金表面制备微弧氧化-溶胶凝胶复合膜层,并于干、湿热交替盐雾腐蚀环境下,对复合膜层的耐蚀性进行研究。结果表明,随腐蚀时间的延长,复合膜层宏观表面出现白色斑点,且斑点数量逐渐增多。微观形貌分析表明,试样原始复合膜层表面存在一定数量的微裂纹及孔洞,随干、湿热交替盐雾腐蚀的进行,复合膜层表面局部应力状态发生变化,膜层表面微裂纹及孔洞减少、减小,裂纹边缘处复合膜层有轻微剥落现象。在干、湿热交替腐蚀环境中,复合膜层划格实验评级结果均为0级,膜基结合状态良好;电化学分析表明,在腐蚀实验过程中腐蚀电位未发生明显改变,均保持在约-1.43 V,复合膜层具有良好的耐蚀性。     

镁合金在硅酸盐体系中微弧氧化膜层的性能研究

利用交流微弧氧化装置对AZ91D镁合金在硅酸盐体系中进行了微弧氧化处理,并通过扫描电镜、电化学测试技术和表面性能测试仪等研究了氧化时间和电流密度对微弧氧化膜层表面形貌、厚度、耐蚀性、摩擦磨损性能和结合力的影响.结果表明：随氧化时间和电流密度的增大,镁合金微弧氧化膜层中微孔的数量减少,但微孔的直径和表面粗糙度增大.膜层厚度随氧化时间和电流密度的增加呈线性增大,但与基体的结合力明显降低.镁合金微弧氧化膜层的耐蚀性和耐磨性随氧化时间和电流密度的增大呈先增大后减小的趋势.镁合金在硅酸盐体系中微弧氧化处理的最佳工艺为氧化时间40min、电流密度0.20A/cm2.     

石墨烯在镁合金表面防护技术中的研究进展

简要介绍了石墨烯及其氧化物在镁合金表面防护技术中的应用现状,分别对化学转化技术、微弧氧化技术、电化学沉积技术和有机硅烷技术制备的石墨烯及其氧化物复合膜层的表面结构和耐蚀性进行了综述,分析了不同复合方法的特点,并指出了石墨烯及其氧化物复合膜层在镁合金表面防护处理技术中的研究发展方向和建议。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.