Corrosion Of Heat Affected Zone Research Articles

Corrosion behavior of metal–composite hybrid joints: Influence of precipitation state and bonding zones

The corrosion behavior of AA2024-T3/carbon-fiber-reinforced polyphenylene sulfide joints was investigated. The joints were exposed to salt spray from one to six weeks. The residual strength of these joints was assessed using lap shear test. The corroded surfaces and interfaces were analyzed using small angle X-ray scattering, scanning electron microscopy, and energy dispersive spectroscopy. Regarding the top surface of the joints, the aluminum part corroded preferably in the heat-affected zone (HAZ). It was demonstrated that the HAZ is more susceptible to corrosion than the stir zone (SZ) due to the anodic sites formed by coarse intermetallic particles and S’(S) phase precipitation. Besides, the macro-galvanic coupling between the zones may also potentialize the corrosion in HAZ as the base material and SZ displayed a lower volume fraction of S’(S) than HAZ. In addition, the corrosion at the interface of the joints was evaluated. Four different stages in the development of corrosion at the interface were identified. At Stage I, the joints showed fast strength degradation (0% to -24% of ultimate lap shear force (ULSF) due to water absorption and NaCl migration into the composite. At Stage II, the strength degradation of the joints was stalled (-24% to -28% of ULSF) due to the protection provided to the bonding area by the reconsolidated layer of polymer at the borders of the joint. The polymeric layer acted as a protective coating on the aluminum surface. At Stage III, the corrosion overcame the polymeric layer by reaching the bonding area of the joint. As a result, the strength of the joints rapidly degraded from -28% to -44% of ULSF. Finally, at Stage IV, one expects generalized corrosion in the bonding area, leading to the final strength degradation of the joint.

An investigation on microstructure and pitting corrosion behavior of 316L stainless steel weld joint

Abstract

Susceptibility of welded X80 pipeline steel to corrosion in simulated soil solution

This work is focused on the corrosion behaviour of weldments in X80 pipeline steel. In order to clarify their susceptibility to soil corrosion, general corrosion and stress corrosion crack experiments were carried out in a simulated soil solution. Based on these results, the heat affected zone (HAZ) demonstrated higher corrosion susceptibility than the base metal and the weld metal. This was due to both the higher intrinsic corrosion rate of the HAZ and the galvanic effects between the HAZ and the other regions of the weldment. Additionally, in slow strain rate testing, corrosion damage in the HAZ resulted in a significant decrease in fracture area reduction and time to failure and an increase in the appearance of brittle failure on the fracture surface compared with the base metal. Elemental segregation and coarse grains appear to be two factors that lead to the high corrosion of HAZ.

Characterization of Intergranular Corrosion in Heat-Affected Zone of Low Carbon 12Cr-Ni Ferritic Stainless Steel

Intergranular corrosion in heat-affected zone of low carbon 12Cr-Ni ferritic stainless steel was investigated by the method of practice Z in ASTM A 763-93. The microstructure of welded joint was characterized using an optical microscope and a scanning electronic microscope. Severe intergranular corrosion (IGC) was only observed in low temperature heat-affected zone (LTHAZ) adjacent to base metals at the back of the welded joints in unstabilized steel. On the other hand, IGC was not observed in the welded joints of stabilized steels. According to the analysis of microstructure, the severe IGC is attributed to both the precipitated phase along the grain boundaries inducing the presence of chromium-depleted zone and the welding residual tensile stress promoting the corrosion. Therefore, stabilized elements addition such as Ti and Nb is required in order to avoid the IGC in welded joint of these steels. Relief residual tensile stress by post weld heat treatment would also be an effective method to avoid the IGC in the welded joints of these steels.