Heterogeneous microstructure and deformation behavior of an automotive grade aluminum alloy

Highlights: • Low-Fe Silafont®-36 Al alloy exhibits a distinctive heterogeneous microstructure. • Residual strains exist at α-Al boundary due to thermal mismatch between Al and Si. • A superior strength-ductility synergy is achieved, without strain-rate dependence. • The alloy exhibits strong coordination deformation and strain hardening capacity. • Enhanced modulus and quality index are attained via high pressure die casting. -- Abstract: Aluminum alloy is today considered as a prime selection for manufacturing lightweight structural components in the automotive industry to increase fuel efficiency and reduce harmful emissions. The aim of this study was to identify the effect of microstructure and strain rate on the tensile deformation behavior of a high-pressure die-cast Silafont®-36 alloy, with special attention to strain hardening behavior and deformation mechanisms. The alloy consisted of randomly oriented primary α-Al phase and Al–Si eutectic structure in a form of heterogeneous microstructures, with Sr-modified Si particles exhibiting a coral-like fibrous network. The local misorientations in most primary α-Al grains was below 1°, suggesting strain-free grains along with some extent of near-boundary residual strains due to the thermal mismatch between aluminum and silicon. A superior strength-ductility combination was achieved, along with enhanced Young's modulus and quality index owing to the unique heterogeneous microstructures. The cast alloy exhibited a smooth deformation characteristic with good coordination deformation and strong strain hardening capacity. Strain hardening exponents evaluated via the equations proposed by Ludwik, Hollomon, Swift, and Afrin et al., respectively, showed basically the absence of strain-rate effect from 1 × 10⁻⁵ to 1 × 10⁻² s⁻¹. During the tensile deformation, crack initiated from the sample surface and propagated through the alternate microconstituents of softer primary α-Al phase and harder eutectic structure.