Study of the Precipitation Hardening Behaviour and Intergranular Corrosion of Al-Mg-Si Alloys with Differing Si Contents

Abstract

The effects of Si addition on the precipitation hardening behaviour and evolution of intergranular corrosion (IGC) of Al-Mg-Si alloys were investigated using hardness tests, scanning electron microscopy (SEM), potentiodynamic polarization measurements, and high-resolution transmission electron microscopy (HRTEM). With an increase of the Si content, the peak hardness of the Al-Mg-Si alloys considerably increased by enhancing the density of the β″ (Mg5Si6) phase inside the grains. The microstructures affecting the IGC performance consisted of MgSi particles, Si particles, Al-Fe-Mn-Si intermetallics, and the precipitate-free zone (PFZ). The IGC susceptibility of the Al-Mg-Si alloys was mainly attributed to the high electrochemical potential difference between the MgSi particles and solute-depleted zones. Excess Si improved the IGC susceptibility of the alloys, mainly due to an increase of the grain boundary MgSi precipitates. Furthermore, the evolution of the IGC process was discussed in detail.

Keywords

• intergranular corrosion
• microstructure
• precipitation hardening
• Al-Mg-Si alloys
• electrochemical potential difference