Effect of Solidification Time on Microstructure, Wettability, and Corrosion Properties of A205-T7 Aluminum Alloys

In the present study, the grain size, second-phase morphology, hardness, water wetting behavior, and corrosion resistance of A205, as a function of solidification time, were investigated. A205 is aluminum–copper alloy that is described in the AA Pink Sheets as “Primarily used for making metal matrix composites” (AA Registration Record Pink Sheets, ISSN: 2377-6722, Footnote 13, Aluminum Association, 2018) and as defined by AMS as a “dilute aluminum/TiB2 metal matrix composite” (AMS D Nonferrous Alloys Committee in Cast aluminum alloy composite 4.6Cu–3.4Ti–1.4B–0.75Ag–0.27Mg (205.0/TiB2/3p-T7P) investment cast, solution, and precipitation heat treated, SAE International, 2014). To study the effect of solidification time, a step sand casting, with varying section thickness, was made and subjected to a modified T7 heat treatment. Optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis were utilized to study microstructure, morphology, elemental composition, and phases in the A205 samples, respectively. Potentiodynamic polarization experiment was used to measure the corrosion resistance of the A205 samples. The casting process was also simulated by use of a commercial software. Conclusions drawn from the simulation process show that larger thickness allows for higher solidification time and greater microporosity. It was observed that solidification time has a direct impact on grain size. The phase identification result shows that the two main phases of the alloys are Al and TiB2, while a modified heat treatment cycle makes a complete solution of copper in the grains. Wetting study shows that surface chemistry is not a controlling factor on contact angles, while corrosion result shows a relationship between solidification time and corrosion resistance of the A205 samples. It was observed that there is almost 70% decrease in corrosion rate from the sample with the least section thickness to the sample with the largest section thickness.