6082铝合金双轴肩FSW接头组织及腐蚀性能

利用光学显微镜及动电位极化曲线技术,研究了12mm厚6082一T6铝合金双轴肩搅拌摩擦焊接头组织形貌及其电化学性能．结果表明,主轴转速600r／min,焊接速度为300mm／min,搅拌头倾角为0°的焊缝组织出现了明显的变化,焊合区组织发生了动态再结晶,形成细小的等轴晶结构;母材的腐蚀形貌比较粗糙,表面有较深的点蚀坑,而接头焊核区表面腐蚀形貌均一,点蚀现象较轻;动电位极化测试表明双轴肩搅拌摩擦焊接头焊核区的腐蚀电压比母材高,耐腐蚀性能比母材好．     

6082铝合金搅拌摩擦焊与MIG焊焊缝的腐蚀性能对比

通过静态失重试验、动电位极化曲线测试及电化学阻抗谱(EIS)试验,在室温0.2mol/LNaHSO3+0.6mol/LNaCl溶液中,对6082铝合金搅拌摩擦焊(FSW)和MIG焊焊缝的耐腐蚀性能进行了初步比较。结果表明:主轴转速1200r/min,焊接速度200mm/min,搅拌头倾角3°时的FSW焊缝与MIG焊焊缝相比,腐蚀电位Ecorr正向移动,平均腐蚀速率v軃和腐蚀电流密度Icorr变小,极化电阻Rp增大。同时,使用扫描电子显微镜(SEM)对静态失重试验试样的表面形貌进行了观察,发现FSW焊缝表面上只出现少量较浅的点蚀坑,而MIG焊焊缝表面的点蚀较为严重。     

6082-T6铝合金搅拌摩擦焊接头耐蚀性能研究

采用铜加速乙酸(CASS)连续盐雾试验和电化学点蚀试验对6082铝合金板材搅拌摩擦焊接头及母材表面的腐蚀行为进行研究,并观察分析腐蚀结果的宏观、微观形貌。结果表明:搅拌摩擦焊焊接接头与母材的耐腐蚀性能相差不大。在盐雾腐蚀初期,最先发生腐蚀的为热影响区,点状腐蚀坑已连接成线。随着腐蚀的继续,耐腐蚀的最佳区域为热机影响区。前进侧和后退侧并无明显差异。电化学试验中焊缝电极电位最大,自腐蚀电流密度最小,腐蚀速率小,腐蚀倾向小;热影响区的自腐蚀电流密度大且电极电位低,耐点蚀性能最差;母材的腐蚀速率和耐蚀倾向居中。     

6082铝合金摩擦搅拌焊缝和熔化极惰性气体保护焊缝电化学性能对比（英文）

利用动电位极化曲线,交流阻抗谱(EIS)和扫描电子显微镜(SEM)测试方法,在室温0.2 mol/L NaHSO_3和0.6 mol/L NaCl的水溶液中,对比研究了铝合金搅拌摩擦焊(FSW)焊缝和熔化极惰性气体保护焊(MIG)焊缝电化学性能。结果表明:FSW焊缝的腐蚀速率低于MIG焊缝和母材的腐蚀速率;FSW焊缝的腐蚀电位高于MIG焊缝和母材的腐蚀电位;FSW焊缝的腐蚀电流密度低于MIG焊缝和母材的腐蚀电流密度;FSW焊缝的极化电阻高于MIG焊缝和母材的极化电阻。所有样品的EIS Nyquist谱图上均有一感抗弧存在;SEM观察表明:仅有少量浅蚀坑出现在FSW焊缝表面。     

异种铝合金搅拌摩擦焊与MIG焊焊缝的腐蚀性能对比

在室温0.2 mol/L NaHSO3+0.6 mol/L NaCl溶液中,通过动电位极化曲线测试,电化学阻抗谱(EIS)试验,静态失重试验,对铝合金搅拌摩擦焊(FSW)和MIG异种焊缝的腐蚀性能进行了对比。结果表明:FSW异种焊缝与MIG异种焊缝、两种母材相比,腐蚀电位Ecorr最大,腐蚀电流密度和平均腐蚀速率最小,极化电阻Rp最大。同时使用扫描电子显微镜(SEM)对失重后试样的表面形貌进行了观察,发现FSW异种焊缝表面平坦均一,而MIG异种焊缝表面比较粗糙。     

2219铝合金搅拌摩擦焊接接头剥落腐蚀机理

采用原位腐蚀试验、静态失重试验、浸泡试验研究了2219铝合金搅拌摩擦焊接接头的剥落腐蚀行为与机理。结果表明:2219铝合金搅拌摩擦焊焊缝腐蚀速率比母材小,焊缝的抗腐蚀性提高;腐蚀从局部点蚀开始,起源于第二相粒子与其边缘的铝基体,第二相粒子作阴极;原位腐蚀2 h后焊核与热机影响区发生晶间腐蚀,母材发生严重的点蚀;均匀分布的第二相粒子与细小的等轴晶组织是焊核区剥落腐蚀敏感性降低的主要原因。     

水溶液中钼酸钠和5083铝合金搅拌摩擦焊缝的交互作用

通过搅拌摩擦焊(FSW)手段,制备出5083铝合金同种焊接头。在室温的0.2mol/L NaHSO3和0.6mol/L NaCl溶液中,通过静态失重法及动电位极化曲线测试,对5083母材及其搅拌摩擦焊焊缝的电化学腐蚀行为进行了对比研究。然后在腐蚀介质中添加一定浓度的钼酸钠作为缓蚀剂,评价了此缓蚀剂对5083母材及其搅拌摩擦焊焊缝的电化学行为的影响。结果表明:焊缝的缓蚀效率要优于母材,钼酸钠为一有效的缓蚀剂。     

6082铝合金摩擦搅拌焊缝和熔化极惰性气体保护焊缝电化学性能对比

基于动电位极化曲线,交流阻抗谱(EIS) 和扫描电子显微镜(SEM)手段 ,在室温0.2M NaHSO3 和 0.6M NaCl的水溶液中,对比研究了铝合金摩擦搅拌焊(FSW)焊缝和熔化极惰性气体保护焊(MIG)焊缝电化学性能。结果表明： FSW 焊缝的腐蚀速率低于MIG焊缝和母材的腐蚀速率;FSW 焊缝的腐蚀电位高于MIG焊缝和母材的腐蚀电位; FSW 焊缝的腐蚀电流密度低于MIG焊缝和母材的腐蚀电流密度;FSW 焊缝的极化电阻高于MIG焊缝和母材的极化电阻。所有样品的EIS Nyquist 谱图上均有一感抗弧存在;SEM观察表明：仅有少量浅蚀坑出现在FSW焊缝表面。     

钼酸钠对2024铝合金及搅拌摩擦焊焊缝缓蚀效率的影响

通过搅拌摩擦焊（FSW）手段,制备出2024铝合金同种焊接接头.在室温0.2mol/L NaHSO3和0.6 mol/L NaCl混合溶液中,添加不同浓度的钼酸钠,通过静态失重法、动电位极化曲线以及交流阻抗谱（EIS）测试,评价了室温下此缓蚀剂对2024母材及其搅拌摩擦焊焊缝的电化学行为的影响.结果表明,焊缝的缓蚀效率要优于母材的缓蚀效率,且随浓度增加而增加,钼酸钠是一种有效的阳极钝化型缓蚀剂,并且其缓蚀作用效果和金属表面状态密切相关.     

6082铝合金搅拌摩擦焊接头组织及腐蚀性能研究

利用光学显微镜及动电位极化曲线技术,研究了8 mm厚铝合金6082搅拌摩擦焊焊缝的组织形貌及其电化学性能.结果表明,主轴转速为1000 r/min,焊接速度为160 mm/min,搅拌头倾角为3°的焊缝组织出现了明显的变化,焊核区组织发生了动态再结晶,形成细小的等轴晶结构,动电位极化测试表明焊缝的腐蚀电压较两种母材的高,腐蚀电流较两种母材小.     

5083铝合金搅拌摩擦焊与MIG焊缝腐蚀性能对比

对5083铝合金FSW（搅拌摩擦焊）和MIG（熔化极氩弧焊）焊缝的微观显微组织和腐蚀性能进行了分析.结果表明,FSW焊缝由细小的等轴再结晶组织构成,而MIG焊缝晶粒粗大,组织不均匀.电化学腐蚀试验表明,主轴旋转频率为300 r/min,焊接速度为160 mm/min,搅拌头倾角为3°的FSW焊缝与MIG焊缝相比,腐蚀电...     

Analysis of the corrosion failure causes of shale gas surface pipelines

A shale gas gathering and transportation pipeline in a good block in Sichuan Province started leaking after less than a year of operation. To investigate the causes of corrosion of the sulfate-reducing bacteria (SRB), optical microscopy, scanning electron microscopy, and X-ray diffraction were used to analyze the corrosion and perforation of the shale gas surface pipeline in conjunction with bacterial corrosion simulation experiments. The results showed that the pipeline material (L360N) conformed to the requirements of the American Petroleum Institute 5 L standard and that extracellular polymeric substances were present in the corrosion pits. The corrosion products mainly included FeCO₃, FeS, CaCO₃, MgCO₃, and Fe mineralization. At 40°C, the uniform corrosion rate of L360N in the simulation experiment was 0.234 mm/a, and the local corrosion rate was 0.458 mm/a. SRB, saprophytes, and iron bacteria were detected in the on-site water medium and corrosion products, indicating that the main causes of shale gas pipeline corrosion are bacterial and CO₂ corrosion.     

Galvanic corrosion of gas tungsten arc repair welds in 17-4PH stainless steel in 3·5% NaCl solution

Abstract

In this paper, the galvanic corrosion of individual components of a 17-4PH repair welded stainless steel in 3·5% NaCl solution was investigated using various dc electrochemical measurements and microscopy. Open circuit potential measurement of the regions in the vicinity of a repair weld [i.e. parent metal, weld metal and heat affected zone (HAZ)] in 17-4PH stainless steel in 3·5% NaCl solution indicated that the most likely galvanic couple was between HAZ and weld with the HAZ acting as the anode and weld metal as the cathode. Slow scan rate potentiodynamic polarisation measurement of pitting potentials revealed a lower passive current density and a higher pitting potential in the weld region, while the HAZ showed the highest passive current density and the lowest pitting potential. Observation of the material after applying an anodic potential close to the pitting potential of the individual weld parts also confirmed the formation of several stable pits in the HAZ but only a few metastable pits in the weld and parent metal zones. Galvanic coupling using a zero resistance ammeter also showed a higher current density in the weld metal/HAZ as compared with the parent metal/HAZ and parent metal/weld galvanic couples. Although, the current densities in all measurements were in the range of a few to tenths of nanoampere per square centimetre, it can still be concluded that the weld metal/HAZ couple has the highest risk of galvanic corrosion among the three individual galvanic couples.     

Effect of pretreatment on electrochemical etching behavior of Al foil in HCl–H2SO4

The aluminum foil for high voltage aluminum electrolytic capacitor was immersed in 0.5 mol/L H₃PO₄ or 0.125 mol/L NaOH solution at 40 °C for different time and then DC electro-etched in 1 mol/L HCl+2.5 mol/L H₂SO₄ electrolyte at 80 °C. The pitting potential and self corrosion potential of Al foil were measured with polarization curves (PC). The potentiostatic current—time curve was recorded and the surface and cross section images of etched Al foil were observed with SEM. The electrochemical impedance spectroscopy (EIS) of etched Al foil and potential transient curves (PTC) during initial etching stage were measured. The results show the chemical pretreatments can activate Al foil surface, facilitate the absorption, diffusion and migration of Cl^? onto the Al foil during etching, and improve the initiation rate of meta-stable pits and density of stable pits and tunnels, leading to much increase in the real surface area and special capacitance of etched Al foil.     

3Cr低合金钢焊接接头腐蚀膜对基体的保护作用

利用扫描电镜分析3Cr低合金管线钢高频电阻焊接头微观组织,采用高温高压反应釜和电化学阻抗测试技术对焊接接头的CO₂腐蚀行为进行研究. 3Cr低合金钢高频电阻焊焊缝和母材的化学成分一致,组织均为铁素体+珠光体,且焊缝组织更加细小、均匀. 失重试验结果表明,焊接接头的腐蚀速率比母材小0.28 mm/年. 电化学阻抗测试结果表明,浸泡时间48和168 h后,焊缝表面腐蚀膜电阻均大于母材,焊缝腐蚀膜对基体的保护性均好于母材. 这是由于焊缝组织分布均匀细小,表面腐蚀膜均比母材均匀和致密. 浸泡48 h时焊缝表面为双层膜结构,母材为单层膜;浸泡168 h时焊缝和母材表面均为单层膜结构.     

The effects of crosshead speed and temperature on the stress corrosion cracking of Cu-30% Zn alloy in ammoniacal solution

Stress corrosion cracking (s.c.c. of Cu-30% Zn alloy in Mattsson's solution (0.05 mol/l CuSO₄ + 0.5 mol/l (NH₄)₂SO₄, pH 7.2) was investigated as a function of temperature (298 K–323 K) and crosshead speed (10^?5 mm/min to 1 mm/min). Crack propagation behaviour in a crosshead speed of 10^?4 mm/min at 298 K was also studied. All tests were carried out using a slow strain rate technique. Cracks occurred intergranularly under all experimental conditions used. At high crosshead speeds (5 × 10^?3 mm/min to 1 mm/min) the susceptibility to s.c.c. increased with increasing temperature. At slow crosshead speeds, however, an inverse effect of temperature on the susceptibility was revealed. Constant crack velocities were obtained in both specimens with or without surface coating, and the velocity in the coated specimen was lower than that in the uncoated specimen by one order of magnitude. Scanning electron microscopic examination revealed that ahead of intergranular cracks small corrosion pits were formed along grain boundaries.Based on the above experimental results, the mechanism of intergranular s.c.c. of Cu-30%Zn alloy was discussed by considering the growth rate of microcrack formed along grain boundary and the corrosion rate (or repassivation rate) of the microcrack.     

Effect of equal-channel angular pressing on pitting corrosion resistance of anodized aluminum-copper alloy

The effect of equal-channel angular pressing(ECAP) on the pitting corrosion resistance of anodized Al-Cu alloy was investigated by electrochemical techniques in a solution containing 0.2 mol/L AlCl₃ and also by surface analysis. Anodizing was conducted for 20 min at 200 and 400 A/m² in a solution containing 1.53 mol/L H₂SO₄ and 0.018 5 mol/L Al₂(SO₄)₃·16H₂O at 20 °C. Anodized Al-Cu alloy was immediately dipped in boiling water for 20 min to seal the micro pores present in anodic oxide films. The time required before initiating pitting corrosion of anodized Al-Cu alloy is longer with ECAP than without, indicating that ECAP process improves the pitting corrosion resistance of anodized Al-Cu alloy. Second phase precipitates such as Si, Al-Cu-Mg and Al-Cu-Si-Fe-Mn intermetallic compounds are present in Al-Cu alloy and the size of these precipitates is greatly decreased by application of ECAP. Al-Cu-Mg intermetallic compounds are dissolved during anodization, whereas the precipitates composed of Si and Al-Cu-Si-Fe-Mn remain in anodic oxide films due to their more noble corrosion potential than Al. FE-SEM and EPMA observation reveal that the pitting corrosion of anodized Al-Cu alloy occurs preferentially around Al-Cu-Si-Fe-Mn intermetallic compounds, since the anodic oxide films are absent at the boundary between the normal oxide films and these impurity precipitates. The improvement of pitting corrosion resistance of anodized Al-Cu alloy processed by ECAP appears to be attributed to a decrease in the size of precipitates, which act as origins of pitting corrosion.     

Controlling End-Grain Corrosion of Austenitic Stainless Steels

SS 304L is widely used as a structural material in applications handling nitric acid such as nuclear fuel processing plants and nuclear waste management facilities. Bar, wire, and tubular products of this material are especially susceptible to end-grain corrosion in nitric acid environment. Such an attack takes place on the tubular and forged surfaces that are perpendicular to the hot-working direction and occurs as localized pitting type attack. This study shows that the possible reasons for the directional nature of end-grain attack are the manganese sulfide inclusions aligned along the hot-working direction and/or segregation of chromium along the flow lines during the fabrication stage itself. It has been shown in this study that controlled solution annealing, laser surface remelting, and weld overlay can be used to avoid/minimize end-grain corrosion. Different annealing heat-treatments were carried out on two heats of SS 304L tube and susceptibility to corrosion was measured by ASTM A 262 practice C and electrochemical potentiokinetic reactivation (EPR) test. Solution annealing at 950 °C for 90 min has been shown to increase the resistance to end-grain corrosion. Laser surface remelting using continuous wave CO₂ laser under argon shield and weld deposition (overlay) using SS 308L material were done on the end faces of the tubes. These samples were completely resistant to end-grain corrosion in nitric acid environments.