Effects of minor Sc addition on the microstructures and mechanical properties of Al-Zn-Mg-Cu casting aluminum alloy

Effects of r%(x=0.15, 0.30, 0.45) Sc addition on the microstructures and mechanical properties of metal-mold-casting aluminum alloy Al-6.0Zn-2.8Mg-l.9Cu were studied. It was showed that addition of Sc could reduce a(Al) grain size, modify a(Al)+η(MgZn₂) eutectic of the experimental alloy, and eliminate Al₇Cu₂Fe phase effectively. It was also found that for the heat treatment experimental alloy, addition of minor Sc could make the second phases along a(Al) grain-boundary and η' meta-stable phase inside α(Al) matrix precipitated more dispersedly, and meanwhile it could promote precipitation of η' phase and decrease its size effectively. The addition of x% Sc element could improve the room temperature ultimate tensile strength of the experimental alloy, but had little effects on its plasticity. The room temperature UTS of the experimental alloy with the addition of 0.45%Sc could reach to 510MPa, the maximum value, among the three Sc-content alloys. In addition, it was also found that addition of 0.30% Sc would improve the high temperature tensile strength of the experimental alloy more apparently than those with 0.15% and 0.45% Sc.