Dealloying-driven local corrosion by intermetallic constituent particles and dispersoids in aerospace aluminium alloys

A Kosari,F Tichelaar,P Visser,H Zandbergen,H Terryn,J.M.C Mol

doi:10.1016/j.corsci.2020.108947

A Kosari, F Tichelaar + Show 4 more

Open Access

https://doi.org/10.1016/j.corsci.2020.108947

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Abstract

Nanoscopic characterization of heterogeneous intermetallic particles (IMPs) which microstructurally and compositionally evolve during local corrosion is crucial in unravelling the mechanisms and sequence of initial and local corrosion events. Herein, we study site-specific initiation events focused on microscopic constituent intermetallic compounds and nanoscopic dispersoids in AA2024-T3 at the nanoscale using a combined quasi in-situ and ex-situ analytical TEM approach. Our findings show a dealloying-driven local corrosion initiation at the studied IMPs that have been considered as cathodic phases traditionally. Besides, local degradation which is a result of galvanic interactions between dealloyed regions of IMPs and their adjacent alloy matrix is largely governed by the intrinsic electrochemical instability of intermetallic compounds.

Highlights

Complex aluminium alloys (AAs) constitute a structural material class with an essential high-strength-to-weight ratio, desirable for aerospace applications [1]
Our findings show a dealloying-driven local corrosion initiation at the studied intermetallic particles (IMPs) that have been considered as cathodic phases traditionally
Time-resolved top-view nanoscopic observations along with complementary cross-sectional post-mortem investigations confirm that cathodic phases evolve microstructurally and compositionally during local corrosion

Summary

Introduction

Complex aluminium alloys (AAs) constitute a structural material class with an essential high-strength-to-weight ratio, desirable for aerospace applications [1]. Constituent phases are formed during solidification at high temperatures and normally not affected by subsequent heat treatments, having a minor contribution to mechanical properties [20,21]. They are relatively large (> 1 μm), irregularly-shaped and rather diverse in chemical composition, containing different amounts of Al, Cu, Fe, Mn and Si and characteristically crystallizing in a variety of atomic structures [22]. Dispersoids like Al20Mn3Cu2 are formed purposefully in the melt for grain refinement, commonly having a submicron size and being nodular-shaped [23]

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