Corrosion Behavior of Selective Laser Melted AlSi10Mg Alloy in NaCl Solution and Its Dependence on Heat Treatment

This work investigates the corrosion behavior of AlSi10Mg alloy produced by selective laser melting (SLM) and the counterparts heat-treated at 450-550 °C in 3.5 wt% NaCl solution. Electrochemical measurements and weight loss tests together with microstructural characterizations were conducted. The SLM-produced alloy displays a microstructure with a continuous network of Si particles, exhibiting superior corrosion behavior. After heat treatment, the Si particles are coarsened and isolated and Al matrix dissolves into their surrounding area, thereby degrading the corrosion resistance properties. Therefore, the corrosion resistance of AlSi10Mg alloy degrades with increasing the heat treatment temperature.     

Corrosion Behavior of 304 Stainless Steel Exposed to a Simulated Salt Lake Atmosphere

The corrosion behavior of stainless steel exposed to a simulated salt lake atmosphere has been investigated by analyzing the evolution of surface morphologies and corrosion products, the initiation and development of pits, and the electrochemical characteristics. The results indicated that(Mg_6Fe_2(OH)_(16)(CO_3)(H_2O)_(4.5))_(0.25), a layered double hydroxide, has been detected for the first time in the corrosion products formed on stainless steel exposed to a simulated salt lake atmosphere. The specimens exposed to MgCl_2 deposit conditions were corroded more severely than those exposed to NaCl deposit conditions, which was attributed to the differences in the deliquescence relative humidity and efflorescence relative humidity values of MgCl_2 and NaCl. In addition, a special corrosion morphology consisting of a concentric circle of yellowish material was observed on the specimens exposed to MgCl_2 deposit conditions, which was attributed to the formation of Mg(OH)_2, inhibiting the diffusion and migration of OH~- ions to the anode region. The maximum pit depth followed a power function with respect to corrosion time. The corrosion mechanism of stainless steel exposed to a simulated salt lake atmosphere is also discussed.     

Induction of pitting corrosion on stainless steel (grades 304 and 316) used in dairy industry by biofilms of common sporeformers

This study hypothesised that there may be induction of pitting corrosion or microbially‐induced corrosion on stainless steel (SS) dairy‐processing surfaces by biofilms of common milk sporeformers such as Bacillus sporothermodurans and Geobacillus stearothermophilus. Scanning electron microscopy (SEM) and micrographs generated from energy‐dispersive spectroscopy were used to observe pitting corrosion and to find the elemental composition and distribution on the control and pitted surfaces. From SEM images and energy‐dispersive spectroscopy micrographs, it was observed that pitting corrosion on SS could be induced by biofilms of both B. sporothermodurans and G. stearothermophilus.     

冶金因素对低合金钢点蚀诱发敏感性的影响

通过极化试验对4种低合金钢的点蚀诱发敏感性作了比较,并结合显微分析对4种钢点蚀诱发敏感性的差异机理做了探讨,结果表明：钢中夹杂物与合金元素是影响低合金钢点蚀诱发敏感性差异的主要原因。     

高锰氮双相不锈钢25Cr-2Ni-10Mn-xW-N的组织和性能研究

研究了钨含量对新型高锰氮双相不锈钢25Cr-2Ni-xW-10Mn-N(x=1.5,3.0,4.5)的显微组织、力学性能以及耐腐蚀性能的影响。结果表明:该系不锈钢固溶处理后具有典型的铁素体+奥氏体双相组织,随着固溶温度的增加,铁素体含量上升。随着钨含量的增加,σ相析出增加,铁素体体积分数增大,耐点蚀性增强,屈服强度上升,断裂延伸率和冲击韧性降低。此类钢作为结构材料具有广阔的应用前景。     

Investigation of the effects of time and temperature of oxidation on corrosion behavior of plasma nitrided AISI 4140 steel

In this paper, the effect of the time and temperature of the post oxidation process on corrosion behavior of AISI 4140 plasma nitrided steel has been studied. Plasma nitriding was carried out at 550 °C for 5 h with a gas mixture of N2/H2:3/1. The plasma nitrided samples were post oxidized for 30 and 60 min with a gas mixture of O2/H2: 1/5 at temperatures of 400 and 450 °C. The treated samples were characterized by optical microscopy, SEM, XRD, roughness testing, electrochemical polarization and salt spray testing. The X-ray analysis revealed the formation of the iron-nitride phases ε and γ′ during plasma nitriding and the iron oxide phases of magnetite and hematite through the post-oxidizing treatment. It was also demonstrated that the corrosion characteristics of the nitrided compound layer were further improved by post-oxidation treatment and that the least corrosion rate and optimum condition relative to pitting corrosion belongs to the oxidized sample at 450 °C for 30 min.     

Corrosion behavior of equal-channel-angular-pressed pure magnesium in NaCl aqueous solution

Effect of microstructure change on corrosion behavior of equal-channel-angular-pressed (ECAPed) pure Mg was investigated. The ECAPed sample after 6 passes obtained finer grains (50-100 μm) compared with as-cast one (800-1500 μm). The strain-induced grain refinement with more crystalline defects weakened corrosion resistance of pure Mg, resulting in more and deeper pits after in-situ corrosion, higher mass-loss rate immersed in NaCl solution, larger I_corr values in polarization curves and lower fitted R_t values in EIS plots. However, the enhanced initial OCP values indicate better weather resistance. Furthermore, corrosion improvement can be expected by reducing defects via subsequent annealing.     

Co-operative corrosion phenomena

The corrosion of aluminium alloy 2024-T3 (AA2024-T3) was studied as a function of immersion time from 2.5 to 120 min in 0.1 M aqueous NaCl solution. At immersion times as short as 5 min, rings of corrosion product of 100 to 200 μm diameter, containing smaller domes of corrosion product, were observed using SEM. The domes of corrosion product had greater chloride concentrations than elsewhere on the surface and represented sites of anodic attack. As the immersion time was increased, significant grain boundary attack was observed within the rings of corrosion product. Analyses of Particle Induced X-ray Emission (PIXE) maps of the corroded surfaces showed a significantly higher number of IM particles around the chloride attack sites than the average particle density for the maps, indicating clustering of IM particles. These results suggest a co-operative corrosion effect as a result of clustering of the IM particles. A mechanism for the generation of the corrosion rings is discussed.     

In-situ investigation on the pitting corrosion behavior of friction stir welded joint of AA2024-T3 aluminium alloy

The surface corrosion behavior of an AA2024-T3 aluminium alloy sheet after friction stir welding was investigated by using an “in-situ observation” method. SEM observations showed that the density and degree of the pitting corrosion in the shoulder active zone were slightly larger compared to the other regions on the top surface. The origins of the pitting corrosion were in the regions between the S phase particles and the adjacent aluminium base. The effect of Al-Cu-Fe-Mn-(Si) intermetallic compounds on the pitting corrosion was attributed to their high self-corrosion potential which induced the anodic dissolution of the surrounding aluminium matrix.     

Comparison of the corrosion of bulk amorphous steel with conventional steel

The corrosion behaviour of one prominent bulk amorphous steel (BAS) alloy, (Fe_44.3Cr₅Co₅Mo_12.8Mn_11.2C_15.8B_5.9)_98.5Y_1.5, is compared to that of its crystalline counterpart and of the conventional steel X210Cr12. In acidic solutions, due to its single-phase nature, the BAS exhibits a much higher stability than the multiphase crystalline counterpart and the conventional steel. With increasing pH value, the overall elemental composition plays a more important role and the reactive elements Mo, Mn and Co, are assumed to be responsible for the observed lower stability of the BAS and its crystalline counterpart as compared to the conventional steel.