Effect of strontium addition, cooling rate and T6 heat treatment on the corrosion behaviour of Al-20%Mg2Si composite

Abstract

Mg2Si reinforced AMCs are considered a promising structural material as the in-situ formation of Mg2Si particle offers excellent matrix/reinforcement stability that allow effective load transfer. Addition of Strontium (Sr) could minimize sharp edges shape of Mg2Si particles in as-cast condition improving the mechanical properties. Incorporating Strontium (Sr) can reduce the sharp-edged morphology of Mg2Si particles in their initial cast state, leading to enhanced mechanical properties. However, existing research on Mg2Si reinforced AMCs does not show sufficient data on corrosion behavior. This research aims to investigate the microstructural changes and corrosion performance of as-cast Al-20 %Mg2Si under various influencing factors including varying solidification rate, addition of Sr and post- fabrication metalwork such as T6 heat treatment. The composite materials were prepared using in-situ casting procedure with high purity of the elements. Microstructure characterization was carried out by optical microscopy, in which the primary Mg2Si particle sizes were measured by image analyser. Corrosion behaviour of the fabricated composite was analysed using electrochemical test. Optical microscopic images reveals that the primary Mg2Si was refined and transform to polyhedron upon addition of 0.01w.t. % Sr into Al-20 %Mg2Si and resulted in improved corrosion resistance upon immersion testing and potentiodynamic polarization testing in 3.5 % NaCl with decreasing the Icorr from 0.80 to 0.41 μA/cm2.The Al-20 %Mg2Si which solidified under lower cooling rate have coarser dendritic primary Mg2Si which results in higher corrosion rate (Icorr = 4.98 μA/cm2). T6 heat treatment transformed the primary Mg2Si to fine dendrites with spherical secondary Mg2Si phase and consequently enhancing the corrosion resistance by decreasing the Icorr to 2.93 μA/cm2.