Anisotropic Inter-granular Corrosion Behaviors and Microstructures of AlMgSiCu Alloy Sheets Made by Thermal-Mechanical Treatments

doi:10.1007/s40195-021-01294-2

Abstract

Abstract:

This study investigates the microstructure and local corrosion behavior of an Al-Mg-Si-Cu alloy, which has been subjected to cold-rolling with different deformation strain ratios (DSRs) and followed by artificial aging. Accelerated corrosion tests show that peak-aged samples with a small DSR (5-10%) are sensitive to inter-granular corrosion (IGC) along both the normal and rolling directions. When the DSR increases to medium strength (20-40%), IGC sensitivity decreases along both directions and corrosion propagates anisotropically. When the DSR is 60-80%, IGC sensitivity along the normal direction continues to decrease, but increases along the rolling direction, indicating pronounced corrosion anisotropy. Microstructural characterization reveals the decreased IGC sensitivity is mainly attributed to a reduction in element segregation at high-angle grain boundaries and the kinked and discontinuous grain boundary corrosion paths. The increased IGC sensitivity along the rolling direction could be related to the significantly flattened grains.

Key words: Al alloys, Local corrosion, Anisotropy, Transmission electron microscopy (TEM), Electron backscattering diffraction (EBSD)

L. M. Liu, Y. X. Lai, C. L. Wu, Z. Zhang, J. H. Chen. Anisotropic Inter-granular Corrosion Behaviors and Microstructures of AlMgSiCu Alloy Sheets Made by Thermal-Mechanical Treatments[J]. Acta Metallurgica Sinica (English Letters), 2022, 35(2): 275-284.

Figures/Tables 11

Fig. 1 Illustration of different corrosion planes and corresponding SEM observation planes. SEM observation planes: cross section a, and rolling plane b. RD, ND, and TD, being rolling, normal, and transverse directions, respectively

Fig. 2 Microhardness versus aging time curves of samples treated with various DSRs. Samples chosen for accelerated corrosion tests, open black circles

Fig. 3 SEM images after IGC tests of R-N cross sections of samples after cold-rolling with different DSRs and 150 °C peak-aging. CR5PA, CR10PA, CR20PA, CR40PA, CR60PA, and CR80PA (a-f, respectively). Inset: observation and corrosion planes; blue arrow: direction of corrosion penetration

Fig. 4 SEM images after IGC tests of rolling planes of samples subjected to cold-rolling with different DSRs and followed by 150 °C peak-aging. CR5PA, CR10PA, CR20PA, CR40PA, CR60PA, and CR80PA (a-f, respectively). Inset: observation and corrosion planes; blue arrow: corrosion penetration direction

Fig. 5 SEM R-N cross-sectional image of the CR5PA sample after IGC tests a. Blue and yellow fonts indicating misorientations of corroded and uncorroded grain boundaries, respectively, and red dashed lines indicating uncorroded LAGBs. IPF map b of the region indicated by green box in a

Fig. 6 EBSD IPF maps of R-N cross-sectional samples subjected to cold-rolling treatment with different DSRs, at 5, 10, 20, 40, 60, and 80% (a-f, respectively)

Fig. 7 EBSD IPF maps of rolling plane samples subjected to cold-rolling treatment with different DSRs, at 5, 10, 20, 40, 60, and 80% (a-f, respectively)

Fig. 8 HAADF-STEM images and corresponding EDS mappings of HAGBs in samples. CR5PA, CR20PA, CR40PA, and CR80PA (a-d, respectively). Red arrows in the HAADF-STEM images showing grain boundary precipitates

Fig. 9 HAADF-STEM images and corresponding EDS mappings of LAGBs in samples. CR20PA, CR40PA, CR60PA, and CR80PA (a-d, respectively)

Fig. 10 HRTEM images and corresponding FFT patterns of typical precipitates at HAGBs a-d, LAGBs e-f

Fig. 11 Illustration of grain structures a-c, and corrosion paths along grain boundaries d-i in samples treated with different DSRs. Small a, d, g, medium b, e, h, and large DSRs c, f, i; corrosion along the ND d-f, corrosion along the RD g-i; red and black curves in d-i denoting corroded and uncorroded grain boundaries, respectively

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