新型高强稀土Al-Zn-Mg-Cu-Sc铝合金的阳极氧化及其抗腐蚀性能研究

针对添加稀土Sc的新型高强7000系铝合金中析出相的特征,发展了相应的阳极氧化工艺,并通过封孔后处理进一步提高膜层的致密性。结果表明,在7000系稀土铝合金表面存在的含Sc析出相作为微阴极,加速其周围Al基体的溶解,影响成膜均匀性。通过调整氧化溶液组成及电参数,在铝合金表面获得了均匀的阳极氧化膜。同时对比了氟锆酸盐、铈盐及沸水3种封孔工艺对阳极氧化膜耐蚀性的影响,结果显示沸水封孔后的阳极氧化膜呈银白色,膜层均匀致密,无缺陷和微裂纹存在,耐蚀性最佳,该膜层盐雾测试336 h未发生腐蚀,可以满足实际工业应用的要求。     

固溶处理对AZ91D镁合金微弧氧化的影响

研究AZ91D镁合金的固溶处理对其微弧氧化成膜的影响.结果表明:固溶态基体由于成分分布均匀而能够迅速成膜并长大,且在相同的微弧化处理时间内其膜层厚度始终大于铸态基体上的膜层厚度,提高幅度约为40%;随反应时间的延长,膜层厚度逐渐增加,微弧氧化膜表面的喷射空洞和喷射沉积物呈现粗大化趋势,膜层表面粗糙度也随之增大;在微弧氧化反应初期,固溶态基体上膜层粗糙度较小;反应约100 S后,固溶态基体膜层的粗糙度逐渐超过铸态基体膜层的粗糙度;当微弧氧化膜厚度相同时,固溶态基体上膜层的粗糙度始终小于铸态基体膜层的;微弧氧化膜上存在微裂纹,铸态基体膜层上的裂纹深而长,呈连续分布且随处可见;固溶态基体膜层上裂纹浅而短,呈单个分布且数量较少;固溶处理带来的基体成分的均匀化能降低微弧氧化生成同厚度膜层的能耗.     

轻合金锆/钛基转化膜的设计及性能研究

通过对传统锆/钛基转化膜成膜机理的分析,提出了提升锆/钛基转化膜性能的设计理念,并分别在5083铝合金和AZ91D镁合金上进行了实践,显著提升了合金基体的耐腐蚀性能及其与有机涂层的附着性能.通过解析影响锆/钛基转化膜性能的关键因素,指出了当前锆/钛基转化膜研究的不足及其未来的发展方向.     

镁合金AZ31化学成膜及其耐蚀性研究

研究了镁合金A731在磷酸盐处理液中的成膜工艺.分析了前处理、工艺条件等因素对化学转化膜质量的影响.利用电化学方法研究成膜过程及膜的耐蚀性能.利用电子探针(EPMA)测定转化膜的表面形貌及化学成分.结果表明,在优化的工艺条件下,所得转化膜均匀致密,对镁合金基体有较好的保护作用,提高了镁合金AZ31的耐腐蚀性能.     

6063铝合金着色钛锆转化膜结构和耐蚀性能的研究

为了获得性能优异的有色钛锆转化膜层,利用正交试验确定了组分为六氟钛酸、六氟锆酸、含锰成膜剂和有机酸的6063铝合金转化处理液的较佳配方,并分析了转化膜的表面形貌、成分及耐蚀性能.分析结果表明:生成的转化膜为淡黄色,且均匀、连续;转化膜中含有钛、锆元素,其腐蚀电位和腐蚀电流密度比裸6063铝合金明显降低,说明钛锆转化膜可以更好地抑制铝合金的阴极反应,从而更有效地提高铝合金的耐蚀性能.     

铝合金钛锆转化膜槽液消耗规律的研究

目的在前期研制的新型铝合金表面钛锆转化膜工艺配方的基础上,进一步探索该新型工艺配方在连续使用过程中的消耗规律。方法通过在连续使用过程中对转化液中主要金属离子(钛、锆、M等)的含量测定分析,找出该成膜剂的消耗规律。采用电化学工作站和SEM对槽液连续使用过程中膜层的耐蚀性能及微观形貌进行表征。结果转化液中的主要成膜成分钛、锆、M的消耗质量比例基本不变,为5:1:4。XPS分析显示,膜层主要由金属氧化物(TiO_2、ZrO_2、Al_2O_3、M_2O_5)、金属氟化物(ZrF_4、AlF_3)和金属有机络合物等组成。随着成膜的不断进行,膜层的耐蚀性能有所下降,自腐蚀电流密度由最初成膜时的0.11μA/cm~2增加到1.24μA/cm~2,但仍低于铝合金基体的自腐蚀电流密度(7.53μA/cm~2)。随着连续成膜,膜层表面的微观裂纹不断变宽,在连续成膜到第80片时,铝合金表面有的位置已经不能成膜。结论钛锆转化液在连续使用过程中,转化液中的主要成膜成分按一定比例消耗,膜层的耐蚀性能随着连续成膜有所下降,因此有必要及时对转化液进行补加和校正。     

第二相对镁基材料微弧氧化过程的影响机制

对含有不同类型第二相的镁基材料进行微弧氧化处理,研究基体材料第二相对其微弧氧化行为的影响规律及其影响机制.利用SEM观察第二相在微弧氧化初期阶段的存在状态,并结合EDS分析第二相的成分及状态变化;通过不同镁基材料在微弧氧化过程中的电压演变趋势分析第二相对微弧氧化行为的影响.根据微弧氧化膜的生长原理,将膜层的生长过程简化等效为一个电容器的反复击穿-重构过程,并依此讨论了微弧氧化膜的形成过程及第二相的影响机理.结果表明,第二相对镁基材料微弧氧化行为的影响与其自身特性密切相关;在微弧氧化的初期阶段,第二相是否具备阀金属特性及其导电特性是影响微弧氧化行为的重要因素.对于具备阀金属特性的第二相,由于其表面能够形成火花放电所必须的阻挡层,因此第二相的存在不会对微弧氧化行为产生明显影响.对于不具备阀金属特性的第二相,其导电特性决定了镁基材料在微弧氧化初期阶段能否正常发生火花放电并顺利进入膜层生长阶段.     

三种不同电解液中镁微弧氧化膜研究

在氟锆酸盐、铝酸盐和硅酸盐3种不同电解液中对镁进行微弧氧化处理分别制得了锆膜、铝膜和硅膜, 对这些膜层的形貌、相组成、表面粗糙度、结合强度、硬度和耐蚀性进行了研究。结果表明：锆膜致密,由t-ZrO2、MgF2和Mg2Zr5O12相组成;铝膜多孔,由MgAl2O4和MgO相组成;硅膜多孔,由Mg2SiO4和MgO相组成。这些膜层表面很粗糙,膜层与基体结合非常牢固。铝膜的硬度比锆膜和硅膜更高。经微弧氧化处理后镁的耐蚀性得到了明显改善,其中锆膜的耐蚀性最好。     

钢铁表面纯锆盐转化膜技术研究现状与进展

锆盐转化膜技术是一种十分重要的环境友好型钢铁表面处理技术,有望完全取代磷酸盐和铬酸盐转化技术。锆盐转化膜的耐蚀性与磷酸盐和铬酸盐转化膜接近,对有机涂层和钢铁基体有着优异的附着力。从纯锆盐转化基本原理、锆盐体系选择、制备方法、转化工艺参数控制、膜层形貌与结构、膜层耐蚀行为、膜层与后续涂层的附着力等方面,对国内外钢铁表面纯锆盐转化膜技术的研究进展和成果进行了综述。纯锆盐转化技术采用的转化液以氟锆酸及其盐为主,制备方法主要是浸渍法。为了获得质量稳定的纯锆盐转化膜,需要控制工艺参数:Zr~(4+)体积分数3%~5%,pH值3.5~4.5,转化时间90 s左右,温度20~35℃。锆盐转化膜一般为100~350 nm厚的双层结构,由纳米颗粒、小结节和聚集体构成,这种结构发挥的锚固作用会显著增加基体与后续涂层的结合强度。但是,锆盐转化成膜机理不够成熟,工艺欠稳定,在实际工业生产应用中仍面临挑战。所以,成膜机制和工艺稳定性的深入探究是未来锆盐转化膜的重点研究方向。     

Mn~(2+)浓度对6063铝合金表面锆基转化膜组织和耐蚀性的影响

为了改善6063铝合金表面锆基转化膜的耐腐蚀性能,利用XRD、SEM、EDS及电化学腐蚀等方法研究了促进剂中Mn~(2+)浓度对6063铝合金表面锆基转化膜的组织和耐蚀性的影响。结果表明,当促进剂中ρ(Mn~(2+))=2.2 g/L浓度时,锆基转化膜比不添加Mn~(2+)时的更致密,但是ρ(Mn~(2+))=4.4 g/L时,转化膜致密性反而下降,不过Mn~(2+)浓度对转化膜厚度的影响不大。本试验制备的锆基转化膜与铝合金基体无明显分界,表明锆基转化膜与铝基体结合良好。并且所制备的转化膜表面属于多孔结构,有利于提高膜与喷涂油漆的附着力。电化学腐蚀性表明,当采用ρ(Mn~(2+))=2.2 g/L Mn~(2+)浓度的促进剂时,转化膜的腐蚀电流密度变小,大约是没有添加Mn~(2+)的1/200,而且极化电压增加,大约是没有添加Mn~(2+)的8.7倍。这些参数表明,Mn~(2+)的加入提高了锆基转化膜的耐腐性。但是Mn~(2+)浓度过大会导致耐腐性下降,甚至不如没有添加Mn~(2+)的转化膜的。     

Electroless Ni-P layer with a chromium-free pretreatment on AZ91D magnesium alloy

A phosphate-manganese conversion film was proposed as the pretreatment layer between Ni-P coating and AZ91D magnesium alloy substrate, to replace the traditional chromium oxide plus HF pretreatment. The subsequent Ni-P deposited on the layer was also characterized by its structure, morphology, microhardness and corrosion-resistance. The pretreatment layer on the substrate not only reduces the corrosion of magnesium during Ni-P plating process, but also reduces the potential difference between the matrix and the second phase. Thus, a Ni-P coating with fine and dense structure was obtained on the AZ91D magnesium alloy, which shows better corrosion resistance than the Ni-P with chromium oxide plus HF as pretreatment.     

Influence of Substrate Material on Plain Fatigue and Fretting Fatigue Behavior of Detonation Gun Sprayed Cu-Ni-In Coating

Cu-Ni-In coating was formulated on two substrate materials—Ti-alloy (Ti-6Al-4V) and Al-alloy (AA 6063) fatigue test specimens using detonation gun (D-gun) spray process. Coating on both substrates was dense with low porosity, high hardness, and high surface roughness. Relatively higher surface compressive residual stress was present at the coating on Ti-alloy specimens. In case of the coating on Al-alloy samples, tensile residual stress was also present in some places. Uniaxial plain fatigue and fretting fatigue experiments were conducted on uncoated and coated specimens. The detrimental effect of life reduction due to fretting was relatively larger in the Al-alloy compared to the Ti-alloy. While Cu-Ni-In coating was found to be beneficial on the Ti-alloy, it was deleterious on the Al-alloy substrate under both plain fatigue and fretting fatigue loading. The results were explained in terms of differences in the values of surface hardness, surface roughness, surface residual stress, and friction stress.     

Thermal stability studies of atmospheric plasma deposited siloxane films deposited on Vycor™ glass

The thermal stability of siloxane films deposited on Vycor glass and silicon substrates using atmospheric pressure plasma was studied. Siloxane films were deposited from a liquid tetraethyl orthosilicate (TEOS) precursor which was nebulised into a helium/oxygen plasma. The thickness of the siloxane films was in the range 1-12 nm as measured using both ellipsometry and X-ray reflectometry. Film composition and chemical properties were examined using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis. The thermal stability of the films was evaluated under argon atmosphere at temperatures up to 700 °C. The films were found to exhibit good adhesion without cracks or delamination after the thermal treatment. A decrease in coating thickness and a reduction in surface roughness was however observed indicating, a change in coating chemistry. This was confirmed by the reduction in carbon concentration observed by XPS. Particulates generated by excess gas phase reaction of TEOS were observed on the surface of the coating. A larger reduction in particulates size was observed after thermal treatment compared with the reduction in thickness of the bulk coating. This indicates that the particulates may have a different composition to that of the coating.     

铁基粉末冶金零件电镀前二次水基防锈溶液的封孔技术研究

目的铁基粉末冶金零件具有特殊的疏松和多孔结构,在前处理、电镀、钝化等过程中易造成零件孔隙的酸、碱、盐等残留,镀后零件在使用过程中也易出现耐腐蚀性能下降或镀层脱落的现象。因此,对铁基粉末冶金零件孔隙进行封闭是一种提高镀层防腐蚀性能和结合性能的有效方法。方法采用一种专用的粉末冶金零件水基防锈封闭溶液,对零件孔隙进行前处理前的第一次封闭和前处理后的第二次封闭。其孔隙封闭原理是在镀前处理前,利用水基防锈溶液中的缓蚀剂、钝化剂等成分的扩散、渗透,在孔隙处发生吸附、钝化及沉淀等反应,来减轻或避免前处理过程中接触到的酸、碱等成分在孔隙的残留;再在电镀前处理后,进行第二次防锈水溶液的封闭处理,可进一步强化粉末冶金零件的钝化封闭效果。结果没有经过防锈水溶液封闭处理的白钝化锌镍合金镀层(滚镀零件),在96 h盐雾试验后,表面出现了轻微的腐蚀;经过一次防锈水溶液封闭处理的锌镍合金镀层,在120 h后出现了轻微的腐蚀;经过二次防锈水溶液封闭处理的锌镍合金镀层,在240 h后未出现腐蚀。结论粉末冶金零件经过这二次封闭处理,再进行电镀Zn-Ni合金及镀层钝化处理,可以有效提高零件表面镀层的耐腐蚀性能和结合性能。     

Effects of Dissimilar Alumina Particulates on Microstructure and Properties of Cold-Sprayed Alumina/A380 Composite Coatings

In this study,alumina/A380 composite coatings were fabricated by cold spray.The influence of alumina particulates' morphology(spherical and irregular) and content on the deposition behavior of the coatings(including surface roughness,surface residual stress,cross-sectional microstructure and microhardness) was investigated.Results revealed that the spherical alumina mainly shows micro-tamping effect during deposition,which result in remarkable low surface roughness and porosity of the coatings.In addition,very low deposition efficiency and good interfacial bonding between the coating and the substrate were achieved.For irregular alumina particles,the embedding of ceramic particulates in the coating was dominant during deposition process,resulting in high retention in the final deposit.However,it showed limited influence on porosity,surface roughness and interfacial bonding of the deposit.The coatings containing irregular alumina particulates exhibited much higher microhardness than those containing spherical alumina due to the higher load-bearing capacity of deposited alumina.     

Structure and formation mechanism of phosphate conversion coating on die-cast AZ91D magnesium alloy

Phosphate conversion coating, which is considered as an alternative to chromium conversion coating for improving the corrosion resistance of die-cast AZ91D magnesium alloy is studied. The structure and formation mechanism of the coating was investigated in details using ESEM/EDX, XRD, EPMA, ICP and electrochemical method. It was found that the conversion coating was composed of complex phosphate containing magnesium and aluminum and showed amorphous structure. The thickness of the coating was about 10 μm. A possible formation mechanism for phosphate conversion coating was proposed. Local pH rise due to the evolution of hydrogen in the vicinity of micro-cathode attributed to the movement of hydrolysis reaction balance for manganese dihydro phosphate in treating solution and resulted in the phosphate coating precipitated on metal surface. Initial depositing position was related to the microstructure of substrate. Galvanic effect between α phase and β phase caused the flower-like phosphate nuclei preferential depositing on β phase. Ball-like phosphate nuclei deposited mainly in α phase interior due to the micro-galvanic effect within α phase. The primary α phase was removed from the metal matrix due to the corrosion dissolution, which suggested the anodic dissolution mechanism during phosphate conversion coating growth. The inner stress in dried film resulted in random distribution of the network micro-cracks on film surface, the crack site did not correspond to β phase.     

Fatigue Crack Nucleation Studies on Sulfuric Acid Anodized 7075-T73 Aluminum

The influence of a sulfuric acid anodic coating process on the fatigue crack nucleation behavior of 7075-T73 aluminum alloy was investigated. Silicone surface replication in combination with carbon sputter coating and scanning electron microscopy (SEM) allowed for in situ monitoring of the number of cycles for crack nucleation. A single edge circular notch (SECN) coupon was designed for the present study to localize fatigue damage thus enhancing fatigue crack detection and capture the effects of multiaxial stress conditions indicative of a majority engineering applications. Linear elastic finite element modeling of the SECN coupon was performed to quantify the von Mises equivalent stress distribution and the stress concentration factor of the notched region. The experimental results indicate that the presence of localized pitting corrosion initiated during the anodic coating pretreatment process had an adverse effect on fatigue performance. Specifically, multiple crack nucleation sites were evident as opposed to a single crack origin for the untreated specimens. Post-cycling SEM surface examinations displayed networks of micro-cracks in the anodic coating emanating from the pits although these were not found to be fatigue crack origin sites during post SEM fractographic exams. Thus, the stress concentration effect of the corrosion pits was found to be predominant. The total cycles to failure on average was reduced by approximately 60% for the anodic coated versus untreated specimens. A strategy is also discussed on how to mitigate accelerated crack nucleation by controlled surface pretreatment and use of a chromated chemical conversion coating in lieu of an anodic coating for selective applications.     

铝合金表面钼酸盐改进植酸转化膜的耐蚀性能

目的通过钼酸钠(SM)添加剂、SM前处理、SM后处理三种方案对铝合金表面植酸转化膜进行改进研究,以进一步提高其耐蚀性。方法通过动电位极化测试研究改进后铝合金在3.5%(质量分数)Na Cl溶液中的耐蚀性。结果随着SM添加剂浓度的增加,铝合金表面植酸转化膜的耐蚀性先增强再减弱,SM质量浓度为30 g/L时的腐蚀保护效率Pe最大,达95.5%,而不含SM时的Pe仅为86.8%。p H值太大(p H=8.0)或太小(p H=3.0)都不利于形成耐蚀性更好的膜层,p H值为6.0时的Pe达98.6%。SM后处理会严重影响植酸转化膜的耐蚀性,腐蚀电流密度Jcorr大幅增大;SM前处理可提高植酸转化膜的耐蚀性,Pe达98.2%;SM前处理与添加剂同时应用时,植酸转化膜耐蚀性提高幅度更显著,Jcorr仅为0.042μA/cm2,极化电阻Rp达222 kΩ·cm2,Pe达99.5%。结论 SM添加剂和SM前处理均可明显提高铝合金表面植酸转化膜的耐蚀性,且复合作用时的效果更显著,而SM后处理不能提高铝合金表面植酸转化膜的耐蚀性。     

高能离子刻蚀前处理对AlTiSiN涂层切削性能的影响

目的提高AlTiSiN涂层与刀具基材的结合强度,降低涂层表面的粗糙度,减少切削过程中涂层的剥落,改善涂层刀具的切削寿命。方法采用离子源增强的多弧离子镀设备刻蚀清理基体材料,并制备AlTiSiN涂层。利用X射线衍射仪(XRD)、扫描电镜(SEM)、粗糙度仪、划痕仪和铣削实验探讨涂层沉积前不同Ar离子刻蚀清洗工艺对AlTiSiN涂层结构、膜基结合力和涂层表面形貌的的影响,探究不同刻蚀清洗工艺对涂层刀具切削机理和切削性能的影响。结果 AlTiSiN涂层的相结构主要由(Al,Ti)N固溶体相组成,涂层沿着基体呈现柱状生长。随着高能Ar离子刻蚀电流由40 A增加至100 A,涂层的表面粗糙度降低,Ra值由140 nm降至69 nm,Sq值由226 nm降至117 nm;涂层与基体之间的结合强度增加,Lc2由41 N增加至52 N;切削加工DC53模具钢结果显示,当清洗电流增加至100 A,涂层的剥落几率降低,涂层刀具的切削寿命增加,由11 m增加至23 m。结论高能离子刻蚀前处理过程可有效增加涂层与基体之间的结合强度,降低涂层表面粗糙度,进而提高涂层刀具的切削寿命。刻蚀清洗所用电流强度越大,清洗效果越好,刀具涂层切削性能提高越明显。     

钛合金表面激光熔化沉积钛基复合材料涂层的组织及性能

通过激光熔化沉积TA15+30%TiC(体积分数)混合粉末,在TA15钛合金表面制备出钛基复合材料涂层,分析了涂层的组织、硬度及界面结合强度。结果表明,激光熔化沉积过程中原始TiC颗粒发生溶解,并在凝固过程中重新析出细小的TiC,TiC有等轴状及枝晶两种形态,涂层中存在部分未熔的TiC颗粒;涂层硬度达HRC 60;涂层与基体界面为完全冶金结合,涂层的界面结合强度大于310 MPa,抗剪切强度为330 MPa;经弯曲及热震试验后,涂层未出现剥落现象,表明涂层与基体具有很好的相容性