Effect of Tungsten Alloying and T7 Heat Treatment on the Corrosion Behavior of AlSi5Cu2Mg Alloy: Electrochemical and Long-term Immersion Study

Abstract

This article presents a systematic study of the effect of tungsten additions as a modifying alloying element and of the subsequent T7 heat treatment on the corrosion stability associated with the microstructural characteristics of the hypoeutectic aluminum alloy AlSi5Cu2Mg. The corrosion resistance of aluminum alloys generally depends primarily on electrochemical potential differences between the solid solution matrix and the present intermetallic phases, whereby targeted microstructural modification can thermodynamically and kinetically stabilize the surface against local galvanic degradation. The aim of this work was to elucidate the combined action of microstructural and electrochemical mechanisms in the experimental alloy. The experimental alloy with graded tungsten additions (0.05, 0.10, and 0.15 wt. % W) was prepared by gravity casting into a metal mold. Corrosion resistance was evaluated through long-term immersion exposure tests in a 3.5% NaCl solution for 20, 40, 60, and 80 days and electrochemical potentiodynamic polarization tests. In the cast state, the addition of tungsten reduces galvanic microcells and shifts the corrosion potential toward more noble values, which was optimally demonstrated at a concentration of 0.15 wt. % W, where the corrosion rate decreased to 0.0192 mm/year. The T7 treatment enabled effective redistribution of copper and magnesium, thereby eliminating the heterogeneous phases (θ-Al2Cu and β-Mg2Si) that cause intergranular degradation. The variant with 0.15 wt. % W after T7 heat treatment, which recorded the lowest corrosion current density (0.69 μA/cm2) and a minimum corrosion rate of 0.0095 mm/year due to the dominant suppression of the corrosion mechanism kinetics and matrix stabilization.