Influence of Gd content on microstructure and mechanical properties of cast Al-12Si-4Cu-2Ni-0.8Mg alloys

The influence of Gd content on the microstructure and mechanical properties of gravity cast Al-12Si-4Cu-2Ni-0.8Mg alloys is reported. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes at different Gd contents. After Gd additions, the Al3CuGd phase forms and the morphology of Al3CuGd phase gradually develops into needle-like. The morphology of the AlSiFeNiCu-Aluminide and some Al3CuNi phases changes from strip-like to small block-like. The secondary dendrite arm spacing (SDAS) first reduces from 23 μm to 16 μm and then increases up to 20 μm when the addition of Gd increases from 0% to 0.1% and further to 0.5%. It turns out that adding 0.1% Gd into alloys can improve mechanical properties when the temperature is below 200 °C. The results show that adding 0.2% Gd into alloys can improve ultimate tensile strength, reduce elongation when the temperature is beyond 300 °C. A typical brittle fracture of untreated and 0.1% Gd treated alloys is dominating till 200 °C and ductile fracture happens during tests beyond 300 °C. However, a typical brittle fracture of 0.2% Gd and 0.5% Gd treated alloys is dominating till 300 °C, and brittle and ductile fracture coexist in 350 °C.