Crystallographic effects on the corrosion of twin roll cast AZ31 Mg alloy sheet

Surajkumar Pawar, Thomas Slater, Timothy Burnett, Xiaorong Zhou, G.M. Scamans, Z. Fan, George Thompson, Philip Withers

    Research output: Contribution to journalArticlepeer-review

    Abstract

    The influence of crystal orientation on the corrosion behaviour of twin roll cast (TRC) AZ31 Mg alloy sheet has been investigated using correlative microscopy and immersion testing in 3.5% NaCl. Corrosion initiates as a consequence of the microgalvanic coupling between cathodic intermetallic phases, including sub-micron sized, rosette-shaped Al8Mn5 particles, β-Mg17(Al,Zn)12 phase and the Mg matrix. Subsequent development of lateral filiform-like corrosion fronts are observed running along the dendrite arms whilst being constrained by the Al- and Zn-rich interdendritic boundaries. Prolonged immersion showed variable corrosion depths across the surface. By correlating with EBSD analysis, it was confirmed that the corrosion depth is considerably higher in α-Mg grains with non-basal planes on the surface. The severity of attack suffered by α-Mg grains with non-basal planes on the surface is on average twice that for grains with basal or near-basal with planes on the surface. At the same time, corroded α-Mg grains with basal planes on the surface display nanoscale, canyon-like corrosion features developing into the alloy perpendicularly. A mechanism has been proposed to explain the sequential corrosion events.
    Original languageEnglish
    Pages (from-to)90-99
    Number of pages10
    JournalActa Materialia
    Volume133
    Early online date23 May 2017
    DOIs
    Publication statusPublished - Jul 2017

    Keywords

    • automotive sheet
    • Mg-Al alloy
    • micro-galvanic corrosion
    • MG dissolution

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