Effect of sizing on the corrosion behaviour of Alumix 123 P/M alloy in 3.5 wt-% NaCl solution

Abstract

The corrosion behaviour of the commercial aluminium powder metallurgy alloy ‘Alumix 123’ after undergone ‘sizing’, a standard cold forming operation, has been studied in naturally aerated 3.5 wt-% NaCl solution through open circuit potential (OCP), cathodic potentiodynamic polarisation, cyclic potentiodynamic polarisation and potentiostatic polarisation experiments, and the subsequent corrosion morphology was characterised by scanning electron microscopy and energy dispersive X-ray spectroscopy. The results were compared to those obtained for Alumix 123 in the ‘as-sintered’ condition and to a compositionally similar wrought alloy, AA2014-T6. The sizing operation significantly affected the OCP, corrosion control, cathodic process, corrosion rate and corrosion morphology of Alumix 123. These changes are attributed to the reduction in open surface porosity brought about by the sizing operation. It appears that with a single secondary operation, sizing, the corrosion resistance of Alumix 123 is significantly improved and approaches that of AA2014-T6.

Keywords:

• Aluminium alloy
• Corrosion
• Electrochemistry
• Powder metallurgy
• Sizing
• Crevice corrosion
• Alumix 123
• AA2014

Acknowledgements

The authors gratefully acknowledge the Natural Sciences and Engineering Research Council of Canada (NSERC) and AUTO21 Network of Centers of Excellence for providing financial support during this work. The authors would also like to thank the Minerals Engineering Centre (MEC) at Dalhousie University for chemical and particle size analyses, the Institute for Research in Materials (IRM) at Dalhousie University for use of the SEM/EDS system, ECKA Granules for supply of the P/M pre-mix, and GKN Sinter Metals for sintering the P/M material.