Mechanical Behavior of a Newly-Developed Aluminum-Silicon Alloy: Study on Multiscale Deformation Mechanisms

Lightweighting is in the spotlight of innovations in the automotive industry owing to the demand of energy-efficient electric and hybrid vehicles. Lightweight aluminum (Al) alloys have been leading this global industrial trend as the primary materials for the structural components of vehicles. Due to the advancement in technologies, Al alloys can be fabricated via novel techniques that can improve certain traits like superior strength-ductility synergy in the same range as that of structural steels. As these industries grow, there is an impending need to tailor the alloy microstructures with a proper control of the process parameters like solidification thermodynamics and kinetics, along with the alloy chemistry. This dissertation begins with the primary goal to understand the deformation behavior of a newly-developed low-iron containing, vacuum-assisted high pressure die-cast aluminum-silicon alloy, commercially named Silafont®-36 alloy under static and cyclic loading conditions. Throughout the several investigations in this work, it was observed that the presence of a heterogeneous microstructure led to increased tensile and compressive strength, and elastic modulus than several other commercial Al-Si cast alloys. The cast alloy showed improved ductility owing to its uniquely modified eutectic structure. Load-bearing ability of the eutectic Si particles, dislocations generated due to thermal mismatch between Al matrix and Si particles, and Orowan looping were found to be the predominant strengthening mechanisms in the cast alloy. The alloy showed improved fatigue resistance and a strong cyclic hardening effect in the cast form. Upon solutionizing and overaging treatments of the cast alloy, changes in the microstructure significantly altered the static and cyclic deformation behavior. A novel method was proposed to evaluate the intrinsic fatigue toughness of the alloy in different conditions, which was established as a material constant. This further served as an important parameter to more accurately predict fatigue life of the alloy in cast and heat-treated conditions. In a nutshell, this work constituted an informative benchmark for unravelling the mysteries of the macro-, meso-, and micro-scale deformation behavior that led to improved mechanical performance of a lightweight automotive-grade Al-Si alloy.