Modification and strengthening mechanism of high strength-toughness as-cast Al–11Si–3Cu alloy modified with minor Sr and Er content

Abstract

The strength of Al–11Si–3Cu requires improvement to meet the growing demands of manufacturing and expand its application in the automotive market. A new high strength-toughness as-cast Al–11Si–3Cu alloy with the ultimate tensile strength and elongation up to 294 MPa and 3.5 % was developed by using minor Sr and Er modifiers. The TEM and the first principles calculations showed that Sr and Er atoms adsorbed on the eutectic Si surface and prompted the formation of twins that branched in 70.5° and 39° directions, and the synergistic effects of Sr and Er atoms significantly reduced the size of eutectic Si to ∼500 nm. Moreover, the ∼10 nm Al3Er and ∼200 nm Al8Cu4Er particles formed in the alloy, which have positive effects on enhancing the mechanical properties of the alloy. The dislocation lines were stretched when passing through the Al3Er particles and eventually formed dislocation rings, while the motion of the grain boundary was hindered by the Al8Cu4Er particle. Additionally, the modification mechanism of Sr and Er modifiers on the eutectic Si and the strengthening mechanism of the modified alloy were discussed.