Solidificação, desenvolvimento microestrutural, propriedades mecânicas, elétricas e de corrosão de ligas Al-Si(-Ag)

Abstract

In the last years, the development of new light and efficient systems in electric vehicles (EV) opens up new research opportunities. Besides that, the need for internal combustion engine components with optimized properties is also attracting interest. One of these challenges involves the development of alternative Al-Si based alloys. Under such context, the microstructure of Al-Si alloys can be modified with addition of alloying elements in order to improve properties such as tensile strength, corrosion resistance and electrical conductivity. This PhD research focuses on better understanding of the effects of Ag additions: 0.1 and 2.0wt.% and cooling rate variations on dendritic growth and eutectic formation constituting Al-5wt.%Si and Al-10wt.%Si alloys. Thermodynamic simulations (ThermoCalc) were performed to support the extensive microstructural evaluation. A complete set of characterization including monitored solidification experiments, tensile tests, electrical conductivity, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), immersion tests, optical microscopy (OM) and scanning electron microscopy (SEM) was developed. The Al-5wt.%Si-0.1wt.%Ag and Al-10wt.%Si-0.1wt.%Ag alloys showed the best combined results for tensile properties / electrical conductivity, resulting in 142 MPa / 22% / 29.4 %IACS and 160 MPa / 12 % / 29.6 %IACS, respectively. Ag-containing having 2.0wt.% alloys resulted in slightly higher mechanical properties and lower electrical conductivity. Furthermore, the Al-5%Si-0.1%Ag and Al-10%Si-0.1%Ag alloys showed the best corrosion performance compared to the ternary compositions with equivalent Si and higher Ag content, resulting in lower corrosion rate, higher passive range, and greater polarization resistance. In the matter of the Al-10wt.% Si-Ag alloys, the microstructure refinement tends to increase the corrosion rate and to enhance the sample’s nobility.