Interfacial microstructures and properties of aluminum alloys/galvanized low-carbon steel under high-pressure torsion

A new composite processing technology characterized by hot-dip Zn–Al alloy process was developed to achieve a sound metallurgical bonding between Al–7 wt% Si alloy (or pure Al) castings and low-carbon steel inserts, and the variations of microstructure and property of the bonding zone were investigated under high-pressure torsion (HPT). During hot-dipping in a Zn–2.2 wt% Al alloy bath, a thick Al₅Fe₂Zn_x phase layer was formed on the steel surface and retarded the formation of Fe–Zn compound layers, resulting in the formation of a dispersed Al₃FeZn_x phase in zinc coating. During the composite casting process, complex interface reactions were observed for the Al–Fe–Si–Zn (or Al–Fe–Zn) phases formation in the interfacial bonding zone of Al–Si alloy (or Al)/galvanized steel reaction couple. In addition, the results show that the HPT process generates a number of cracks in the Al–Fe phase layers (consisting of Al₅Fe₂ and Al₃Fe phases) of the Al/aluminized steel interface. Unexpectedly, the Al/galvanized steel interface zone shows a good plastic property. Beside the Al/galvanized steel interface zone, the microhardnesses of both the interface zone and substrates increased after the HPT process.     

焊缝余高对铜镍合金管材腐蚀行为的影响

海水管道焊缝下游区是发生腐蚀的热点区域.为探究B30管道焊缝余高对与其下游区腐蚀行为的影响,利用原位电化学测试装置和自制循环海水冲刷装置,在3天、7天、15天、30天4个冲刷节点进行试验.测试了3种模拟焊缝余高(0 mm;0.5 mm;1.5 mm)在紧邻热影响区和下游30 mm处母材区的电化学阻抗谱,用扫描电镜观察了试样表面的腐蚀形貌,结合COMSOL软件建立了有限元仿真流态模型,探讨了余高对介质流态的影响.结果表明,在有焊缝情况下,热影响区和母材区阻抗值均小于无焊缝结构,焊缝结构会加速下游区的腐蚀,且余高越大,腐蚀倾向也越大;热影响区腐蚀速率均大于母材区;流态模型显示出在热影响区位置出现了涡流,涡流加速了热影响区的腐蚀.     

螺旋护套自动缠绕装置设计

目的为了提高螺旋护套缠绕效率,降低劳动强度,提出一种螺旋护套自动缠绕装置。方法该装置由夹持旋转机构和导向机构组成。夹持机构通过气动控制实现管段的固定,并通过同轴传动实现管段旋转。螺旋护套在导向机构的限制作用下,通过螺旋传动的方式,完成自动缠绕。采用有限元分析法对管段在夹爪夹持过程中的变形进行分析,为夹持机构对管段夹持是否造成损伤提供依据。结果测试结果表明,装置可完成直径6~14 mm直管段的螺旋护套的缠绕,在保障缠绕质量的情况下,缠绕效率较人工提高了7.2倍。结论此装置的设计实现了在直管段螺旋护套的自动缠绕,降低了劳动成本,提高了螺旋护套缠绕的生产效率。     

Q235碳钢在静止和流动条件下的腐蚀不均匀性研究

目的研究Q235碳钢在静止和流动条件下腐蚀程度和主要腐蚀区域的差异。方法使用丝束电极(WBE)技术和电化学阻抗谱(EIS)技术分别研究了WBE在静止和流动条件下的电流密度分布、电荷转移电阻以及腐蚀形貌的变化和差异,同时分析了电极的极性转换现象。结果流动条件下Q235碳钢的电荷转移电阻明显降低。在静止条件下,Q235碳钢表面阳极电流区域所占的最大比例为47%,且阳极电流峰集中出现在WBE的中间区域,而四周边缘处的阳极电流峰较少。在流动条件下,Q235碳钢表面的阳极电流区域所占的最大比例为58%,阳极电流峰随机分布在整个WBE表面,且电流分布区间明显变窄。浸泡在静止条件下的58~#电极和流动条件下的39~#电极发生了多次极性转换现象。结论 Q235碳钢在静止和流动条件下均发生了明显的不均匀腐蚀现象。流动条件加剧了Q235碳钢的腐蚀且降低了腐蚀不均匀性。静止条件下Q235碳钢的腐蚀区域集中在中间区域,流动条件下Q235碳钢的腐蚀区域随机分布在整个碳钢表面。静止和流动条件下的钢电极均发生了电流的极性转换现象。     

Mg-Gd-Y-Zr合金TIG电弧熔覆层微观组织演变及力学性能研究

目的 在AZ91D镁合金表面熔覆Mg-Gd-Y-Zr合金,分析熔覆层微观组织演变规律及其对熔覆层力学性能的影响。方法 采用直流脉冲钨极氩弧焊（DC PTIG welding）,在不同平均电流下,将Mg-Gd-Y-Zr合金焊丝送入AZ91D镁合金熔池,制备熔覆层。采用金相显微镜、扫描电子显微镜、能谱仪及X射线衍射仪,分析不同平均电流条件下的熔覆层微观组织。基于显微维氏硬度仪与往复式滑动摩擦磨损设备,表征熔覆层硬度及摩擦学性能。结果 熔覆层微观组织主要由α-Mg、Mg24(Gd,Y)5及Al2(Gd,Y)相组成。熔覆层呈现明显分层特征,主要是由晶界Mg24(Gd,Y)5相分布差异造成。平均电流增大,熔覆层中心晶粒尺寸先保持不变,而后快速增大,Al2(Gd,Y)相由细小弥散颗粒变为团聚状分布,晶界Mg24(Gd,Y)5相则由连续网状演变为不连续岛状,直至变为细小颗粒状。熔覆层硬度随平均电流增加,呈现略微上升,随后快速下降的趋势,其最高硬度达90.8HV。摩擦磨损测试过程中,平均电流为110 A所得熔覆层失重速率小于AZ91D基材。结论 采用DC PTIG在AZ91D基体表面成功制备了耐磨性能优于基体的含Gd、Y稀土元素的熔覆层,稀释率决定熔覆层Al2(Gd,Y)相形貌及分布规律。     

路灯灯管支架断裂失效分析

目的研究路灯灯管支架出现批量断裂失效的原因。方法通过化学成分分析、力学性能分析、断口扫描分析、金相组织分析、能谱分析等测试手段,对灯管支架的断裂模式及失效原因进行了分析。结果材料中存在贯穿性的带状硅、钙类非金属夹杂物,严重破坏了组织连续性;同时,晶界析出过多链状或断续网状三次渗碳体,导致了晶界脆性增大。结论材料内部缺陷会严重降低材料综合力学性能,通过对原材料冶炼工艺及后续热处理工艺进行改进,问题得到了有效解决,杜绝了此类失效事故再次发生。     

镀锌板在不同加速腐蚀环境下的腐蚀行为研究

目的研究中性盐雾环境、中性盐雾加周浸环境和中性盐雾加湿热环境下镀锌板的腐蚀行为,明确不同加速腐蚀试验环境对镀锌板腐蚀行为的影响。方法对镀锌板进行中性盐雾、中性盐雾加周浸、中性盐雾加湿热等不同类型的加速腐蚀试验,通过失重法、SEM、XRD以及极化曲线等方法,对比不同加速腐蚀试验类型对镀锌板腐蚀行为的影响。结果在三种加速腐蚀试验环境下,镀锌板的腐蚀过程基本相同:镀锌层及白色锌锈腐蚀、锌层破裂、锌层完全脱落、基体碳钢腐蚀。腐蚀产物都以Zn(OH)_2、γ-FeOOH、ZnO、Fe_2O_3等为主。三种环境下镀锌板的腐蚀都不均匀,不同位置的腐蚀情况存在一定差异。其中,中性盐雾环境下材料腐蚀情况最为严重,中性盐雾加周浸环境次之,中性盐雾加湿热环境下最轻。结论三种加速环境都是主要通过Cl~-在锌表面的沉降和溶解作用增强介质的导电性能,加剧锌层的腐蚀。在中性盐雾环境中,Cl~-浓度最高,试样腐蚀最严重。在中性盐雾加周浸环境中,SO_4~(2-)与Cl~-协同作用,腐蚀也较严重。而中性盐雾加湿热环境中,Cl~-被稀释,腐蚀情况最轻微。     

等离子喷涂 NiCr-Cr3C2基复合自润滑涂层的组织及摩擦学性能

将NiCr-Cr3C2复合粉和Ni包MoS2粉按不同比例混合,制成三种喷涂粉末,采用等离子喷涂技术在304不锈钢表面制备复合自润滑涂层,并对涂层的物相组成、显微组织及摩擦磨损性能进行了研究。结果表明:三种涂层的物相组成相同,主相均为Cr7C3,Ni和MoS2;涂层与基体的结合为机械结合,孔隙率较低,表面有少量微裂纹;喷涂粉末中的Ni包MoS2粉偏少或偏多都会导致涂层的摩擦磨损性能变坏,Ni包MoS2粉质量分数为30%时,涂层的摩擦系数及磨损率最低,分别约为0.36和3.3×10-4mg/s。     

Mechanical and barrier properties of MOCVD processed alumina coatings on Ti6Al4V titanium alloy

This study focuses on the implementation of different aluminum oxide coatings processed by metal-organic chemical vapor deposition from aluminum tri-isopropoxide on commercial Ti6Al4V titanium alloy to improve its high temperature corrosion resistance. Films grown at 350 °C and at 480 °C are amorphous and correspond to formulas AlOOH, and Al₂O₃, respectively. Those deposited at 700 °C are composed of γ-Al₂O₃ nanocrystals dispersed in a matrix of amorphous alumina. Their mechanical properties and adhesion to the substrates were investigated by indentation, scratch and micro tensile tests. Hardness and rigidity of the films increase with increasing deposition temperature. The hardness of the coatings prepared at 350 °C and 480 °C is 5.8 ± 0.7 GPa and 10.8 ± 0.8 GPa respectively. Their Young's modulus is 92 ± 8 GPa (350 °C) and 155 ± 6 GPa (480 °C). Scratch tests cause adhesive failures of the films grown at 350 °C and 480 °C whereas cohesive failure is observed for the nanocrystalline one, grown at 700 °C. Micro tensile tests show a more progressive cracking of the latter films than on the amorphous ones. The films allow maintaining good mechanical properties after corrosion with NaCl deposit during 100 h at 450 °C. After corrosion test only the film deposited at 700 °C yields an elongation at break comparable to that of the as processed samples without corrosion. The as established processing–structure–properties relation paves the way to engineer MOCVD aluminum oxide complex coatings which meet the specifications of the high temperature corrosion protection of titanium alloys with regard to the targeted applications.