Research on simulation testing of humidity-controlled salt spray corrosion environment for electrical products under working conditions

Electrochemical Impedance Spectroscopy was utilized to investigate the corrosion behavior of carbon steel in a salt spray test (SST) chamber. The salt spray was applied using 5% NaCl solution at 35 °C. A two-electrode cell comprising a pair of identical carbon steel electrodes embedded in epoxy resin were placed at six different angles (0°, 30°, 45°, 60°, 75°, and 90°) to the horizontal in the chamber. The corrosion rate (CR) of the carbon steel samples and the thickness of the solution film formed on the sample surface were evaluated from the impedances at low and high frequencies, respectively. The CR of carbon steel fixed horizontally (0°) exhibited a low value compared with that fixed at other angles. When the angle changed from 30 to 75°, the solution film thickness decreased greatly, but there was no significant difference in the CR. The CR of carbon steel under the employed SST conditions was more than five times higher than that in a bulk 5% NaCl solution under natural convection. The corrosion mechanism of carbon steel in the SST chamber is also discussed.

Microstructure formation and corrosion behaviour in HVOF-sprayed Inconel 625 coatings

In the present study, a galvanized steel and a AA6082 aluminum alloy sheet of 2 mm thick were weld-brazed by applying laser and using 2-mm-diameter solid Al-12% Si filler wire at 2.5 m/min wire feed rate and 2 m/min laser scan speed at varying laser power (4.0, 3.5, 3.0 kW) in flange configuration. The microstructural investigation of the laser weld-brazed joints revealed the presence of two-layered intermetallic compound at steel/braze seam interface. The corresponding x-ray diffraction analysis of the steel/braze seam interface showed the presence of Al-Fe-Si-based ternary intermetallic phases. SEM and EDS analysis of the braze seam revealed the presence of α-Al grains surrounded by Mg2Si phase in the grain boundary region. Fine intermetallic layer was observed at lower heat-input condition. The corrosion performance of the brazed joints was studied with the help of immersion, salt spray, and electrochemical polarization tests in different electrolytes containing NaCl salt. Brazed joints experienced galvanic corrosion during immersed in corrosive media. From the salt spray test, it was revealed that galvanized steel was highly susceptible to corrosion compared to Al-rich phase. The polarization results showed a substantial change in corrosion resistance from steel interface to the brazed region due to the variation in microstructure. The samples brazed with low heat-input showed better corrosion resistance as compared to the joints made with high heat-input. Post-corrosion microstructure revealed intergranular corrosion at the brazed joint along with pit formation.

Corrosion resistance of the electro-galvanized steel treated in a titanium conversion solution

Self-piercing riveted (SPR) joints in automobiles inevitably suffer from corrosion damage and performance reduction. In this work, the influence of salt spray corrosion on the mechanical properties of TA1-Al5052 alloy SPR joints was studied. The TA1-5052 SPR joints were prepared and salt spray tests were carried out for different durations. The static and fatigue strengths of the joints after salt spray corrosion were tested to analyze the effect of salt spray duration on the performance of the joints. The results show that the joints’ static strength and fatigue strength decrease with prolonged salt spray time. The salt spray duration affects the joint’s tensile failure mode. The tensile failure without corrosion and with a short salt spray time is the fracture failure of the lower aluminum sheet, and the tensile failure of the joints after a long time of salt spray corrosion is the failure of the rivets. The fatigue failure form of the SPR joint is the formation of fatigue cracks in the lower aluminum sheet, and salt spray time has little effect on the fatigue failure form. Salt spray corrosion can promote the initiation and propagation of fatigue cracks. The fatigue crack initiation area is located at the boundary between the lower aluminum sheet and the rivet leg. The initiation of cracks originates from the wear zones among the sheet metal, rivets, and salt spray particles.

The effect of 200 days of cyclic weathering test (CWT) and 1,000 h of salt spray test (SST) on the performance of polyurethane (PU) coating was investigated. A 200 μm coating was applied to a composite and cured before CWT and SST ageing studies. CWT was conducted in ten cycles (each cycle: −40°C for 5 days, 70°C for 5 days, 40°C and 90% RH for 5 days, and salt fog for 5 days). Initial water immersion tests concluded that the coated specimens have 37% less water absorption than uncoated specimens. The degradation behaviour of the coating was evaluated by measuring pull-off adhesion strength, critical load from the scratch test, and wear depth from the pin-on-disk test. Similarly, the surface characteristics of the coating were studied by SEM, gloss value, and contact angle. CWT ageing caused a decrease in gloss value (93–78 GU), pigment content (18–8 wt%), contact angle (92–70°), and an increase in wear depth at 20 N of applied load (45–200 µm). Similarly ageing also decreased the pull-off adhesion strength to 6.77 MPa (CWT) and 7.93 MPa (SST). CWT and SST also decreased the thermal stability by 11–13°C, considering 5 wt% loss and tensile strength of the coating from 42 to 29 MPa. The damage to the composite substrate was not significant due to prolonged exposure periods under CWT and SST, though the damage was noted in PU coating, like increased surface roughness and wear depth.

Low-cost manufacturing in the electronics industry is becoming more demanding, particularly in the production of consumer electronics. Such manufacturing processes require reliable and low-cost lead-free solders. Among the low-temperature lead-free solders, eutectic Sn-Bi solder attracts a great deal of interest as it offers good reliability compared with that of Sn-Pb solders. In this paper, the reliability of eutectic 42%Sn-58%Bi (wt.%) lead-free solder is studied using combinations of environmental tests such as thermal aging (TA) at 100 °C, salt spray test (SST), and a sequential combination of TA and SST. Microstructural studies on the samples are performed at different time intervals. To study the effect of salt spray and TA on the mechanical reliability, drop testing is performed on the samples. Failure analysis is conducted after different tests. Marked corrosion is seen after the SST. This also has a considerable effect on the impact strength of the solder interconnections. TA increases the thickness of the intermetallic layers, which is found to affect the drop performance.

The corrosion performance provided by two anodizing treatments aiming at obtaining films with comparable thickness but different pore morphology was evaluated by immersion, salt spray, and a hybrid tests. The hybrid test was performed in cycles by alternating between immersion and salt spray tests. The corrosion progression was evaluated at selected times by electrochemical impedance spectroscopy (EIS). The EIS indicated that, during immersion test, the self-sealing of the pores due to the precipitation of aluminium hydroxide was favored, and it provided a substantial contribution to the improved corrosion resistance. Vice versa, during salt spray testing, the continuous flow of electrolyte promoted aluminium oxide film dissolution. The EIS study was complemented by the surface appearance and composition of specimens before and after exposure using Field Emission-Scanning Electron Microscopy (FE-SEM) and Energy Dispersive X-ray (EDX) analysis. Overall, the relative performance of the anodic oxides was shown to be dependent on the exposure conditions. In fact, an anodic film with finer pores behaved better during immersion tests, whereas films with coarser pores provided better corrosion protection during salt spray testing.

Degradation of fluorinated polyurethane coating under UVA and salt spray. Part I: Corrosion resistance and morphology

The corrosion resistance of 33 different conversion coatings applied to five different aluminum alloys was tested by salt spray exposure and electrochemical impedance spectroscopy (EIS). Results derived from the two tests were evaluated to determine if a relationship existed. Individual salt spray test panels, with an area of 30 in.2, were visually inspected at regular intervals up to 168 hours of exposure. At each inspection interval, panels were assigned a pass rank if less than 5 pits were observed, or fail rank if more than 5 pits were observed. EIS data were analyzed using a simple equivalent circuit which yielded a “coating resistance”, Rc, which was used as a figure of merit to assess coating performance. Examination of the data showed that both tests could be sensitive discriminators of corrosion protection, but that EIS was more discriminating in the extremes of coating performance. Analysis showed that the probability of achieving a passing salt spray result increased as Rc increased. In the regimes where both tests were sensitive, regression analysis showed that linear relationships could be constructed between the log of Rc and the probability of a coating meeting the pass/fail criterion in salt spray. Based on these relationships, threshold Rc values have been proposed to define the minimum value for which a given coating can be expected to attain a passing result in a 168 hour salt spray test. These values ranged from 2 to 5 x 106 ohm•cm2 for 356, 2024-T3 and 7075-T6,1.5 x 107 ohm•cm2 for 7075-T6, and 2.3 x 107 ohm•cm2 for 3003.

Effects of salt spray test on lead-free solder alloy

The corrosion behavior of low alloy steels, such as 27SiMn, 30CrMnSi, 30CrMnTi, 40Cr and Q550 was studied comparatively in high-mineralized coal mine water, tap water and NaCl solu- tion by means of immersion test, salt spray test and electrochemical methods as well as XRD and SEM with EDS. The results showed that elements Cr and Si can significantly affect the corrosion resistance of low alloy steels: in chloride containing media, Si exhibits stronger effect than Cr on the corrosion; whereas in the presence of oxygen (water and gas phase), Cr exhibits stronger effect than Si. Therefore, 30CrMnTi and 40Cr have better corrosion resistance in the coal mine water. The corrosion behavior of the low alloy steels in the coal mine water depend not only on the role of alloying elements but also on the compactness of the formed limescale induced by mineral ions.

Corrosion behaviour in salt spray and in 3.5% NaCl solution saturated with Mg(OH)2 of as-cast and solution heat-treated binary Mg–RE alloys: RE=Ce, La, Nd, Y, Gd

Characterization of silicon-based chromium (VI) replacement coatings by using time-of-flight secondary ion mass spectrometry and salt spray tests

Electrochemical behavior of ultrahigh strength (UHS) steel (1#) after salt spray test (SST) was studied by means of electrochemical techniques and scanning Kelvin probe, Raman spectroscopy, and scanning electron microscope. The results show that pitting occurs to the samples of 1# steel in SST with 5% NaCl. The corrosion products are mainly γ-FeOOH and oxide/hydroxide of chromium. Within 4 days, corrosion reaction is resisted by the completed corrosion products, and thereafter corrosion rate of 1# steel with corrosion products is accelerated as the SST continues, since the corrosion potential shifts to negative direction and corrosion current density becomes larger. Kelvin potentials of 1# steel after the SST are 0.3-0.4 V higher in magnitude and distributes more unevenly than that before the SST, because the oxide films grow thicker and affect the anodic reaction of corrosion process.