Effects of Sc or/and Ge addition on microstructure and mechanical properties of as-cast 6016 Al alloy

The present work is conducted to study microstructure and mechanical properties of as-cast 6016 Al alloy modified with Sc or/and Ge. Thermodynamic calculation, composition analysis, microstructure examination and mechanical tests have been carried out to show significant effects from Ge and Sc additions. The addition of Ge, as mainly composed of α-Al, Mg₂Si and Si particles, brings forth new formation of Mg₂Ge, and induces eutectic structure forming at grain boundaries (GBs) and nanoscale Si particles in grain interiors (GIs), as a substitution for flaky Mg₂Si phase. The addition of Sc introduces primary Al₃Sc, which obviously refines coarse dendrites of 6016 Al alloy into euiaxed grains, and then stimulates formation of primary AlSc₂Si₂, thus refining Si and Mg₂Si phases. Accordingly, yield stress (YS) of as-cast 6016 Al alloy is moderately increased by Ge addition while obviously enhanced comprehensive properties by Sc addition. An optimal combination of 218 MPa in tensile strength and 22% in elongation to failure (EL) is obtained for 6016 with addition of 0.5% Sc and 0.2% Ge. Different roles of Ge and Sc in adjusting the microstructure and mechanical properties have been discussed.