This paper examines the corrosion behavior of the welding heat-affected zone (HAZ) of HDR (high chromium, duplex, corrosion-resistant) duplex stainless steel, which currently faces corrosion-related challenges in marine seawater systems. The corrosion behavior of the HAZ was studied using microstructure analysis, polarization curve experiments, and double-loop potentiodynamic reactivation experiments. The results show that (1) the covering welding current can promote the formation of austenite in the HAZ, and that the covering welding current has no strict correspondence with the formation of austenite; (2) increasing the welding gap properly can facilitate the formation of austenite; (3) increasing the covering welding current enhances the material’s pitting resistance, and a covering welding current of 70 A, coupled with a covering welding current of 100 A, represents a reasonable choice in terms of achieving a stronger pitting resistance; (4) in terms of intergranular corrosion resistance, increasing the covering welding current is not conducive to the intergranular corrosion resistance of the material, as the covering current will promote the precipitation of the secondary phase at the grain boundary, thus reducing its intergranular corrosion resistance; and (5) reducing the welding current appropriately contributes to improving the stability of the grain boundary.

Cathodic protection is widely used for metal corrosion protection. To improve their performance, it is necessary and urgent to study the influence of metal oxides on the microstructure and performance of aluminum alloy sacrificial anodes. Taking an Al-Ga-In sacrificial anode as the research object, the dissolution morphology and current efficiency characteristics were studied by means of electrochemical testing and microstructural observation, and the influence of varying Pb and Bi contents on the performance of an aluminum alloy sacrificial anode was investigated. The test results reveal that: (1) The Al-Ga-In sacrificial anode with 4% Pb and 1% Bi contents exhibits the best sacrificial anode performance. (2) The inclusion of an appropriate Bi element content shifts the open-circuit potential in a negative direction and promotes activation dissolution. Conversely, excessive Bi content leads to uneven dissolution, resulting in the shedding of anode grains and greatly reducing the current efficiency. (3) During the activation dissolution of the aluminum alloy, the second phase preferentially dissolves, and the activation point destroys the oxide film, resulting in the dissolution of the exposed aluminum matrix. Consequently, the concentration of dissolved metal ions is reduced and deposited back on the surface of the anode sample, promoting the continuous dissolution of the anode.

In order to determine the effect of damaged insulating enamel on the corrosion of high-chromium (H), duplex (D), and corrosion-resistant (R) duplex stainless steel, the corrosion characteristics of HDR duplex stainless steel in 3.5% NaCl solution were studied by means of local electrochemical impedance spectroscopy (LEIS) and micro-morphology analysis. It was shown that the LEIS impedance was stable at about 7.0 × 10³ Ω within 10 days when the HDR duplex stainless steel was not coated. The minimum LEIS impedance of exposed HDR at the damaged area fluctuated around 6.5 × 10³ Ω within 15 days when the coating of the self-control insulating enamel damaged area was 1 mm × 10 mm. The coating-damaged area from 1 mm × 10 mm reduced to a circular hole with a diameter of φ1 mm, and the LEIS impedance of the exposed HDR increased at the damaged coating. When extending along the damaged coating to the intact coating area, the impedance rapidly increased, and the further the distance from the damage, the greater the increase in impedance. The impedance of coated HDR increased with the prolongation of immersion time and ultimately stabilized. The thicker the coating, the longer the impedance took to reach a stable state. The stabilized coating had a better effect on improving the corrosion resistance of HDR duplex stainless steel. Within 15 days, the HDR ferrite structure at different areas of coating damage prioritized corrosion. Cl⁻ mainly comes from the solution, and Si and S elements mainly come from elements of the collective itself, with Cl⁻ adsorption, S, and Si element inclusion being the main factors influencing the corrosion of the ferrite structure.

Aiming at the actual corrosion problem of HDR duplex stainless steel used in marine seawater system, this paper studies the corrosion behavior of welded joints. The corrosion behavior of welded joints was studied by means of microstructure analysis, potentiodynamic polarization xperiment and double-ring potentiodynamic reactivation experiment, and the influence of welding process parameters on the corrosion resistance of HDR duplex stainless steel welded joints was nvestigated. The results show that: (1) The backing welding current has obvious influence on the microstructure of weld metal of HDR steel. The grains in the lower part of the weld are smaller, the quantity is high. (2) The backing welding current has obvious influence on the microstructure of the heat affected zone of HDR steel welded joint, and heat treatment promotes the transformation from ferrite to austenite in the heat affected zone. (3) The ratio of two phases is closer to 1, and the weld metal has better intergranular corrosion resistance in DL-EPR experiment; When the chromium content is low, the intergranular corrosion resistance of weld metal is poor; With the ncrease of welding gap, the Ra value of weld metal increases gradually, and the intergranular corrosion sensitivity increases gradually.