Effect Of Y, Sc And Aging Treatment On Microstructures And Properties Of A357 Alloy

A357 alloy is a kind of typical hypoeutectic Al-Si-Mg alloy. It is widely used in aerospace, automotive and other industrial fields because of its excellent casting properties and mechanical properties. In order to increase the mechanical property of the alloy, the paper uses the optic microscope, XRD, SEM and mechanical property testing equipments to study the effect of Sc, Y and Al-5Ti-1B on the microstructures and properties of the alloy,and the process of refinement and modification will be optimized to improve the microstructures and mechanical properties.The research shows that 0.3%Y and 0.3%Sc can refine α-Al obviously, but the refinement of Y is much worse than that of equally adding Sc. 0.3%Y and 0.2%Sc can modify eutectic Si; however the modification efficiency of Y is much better than Sc. Compared with Sc, Y can improve the mechanical property of the alloy more obviously.The union addition of Y with Al-5Ti-B and Al-10 Sr does not interfere in A357 alloy. Adding Y with traditional Al-5Ti-B and Al-10 Sr makes the SDAS of α-Al range from 15.4 um to 14.1 um, and adding Y can improve the Al-10 Sr modification effect on eutectic silicon. The tensile strength and the elongation of A357 alloy can be improved by 4.5% and 0.5% by adding Y.On the basis of adding Al-5Ti-B and Sr, adding Y will not change the best solution temperature and aging temperature of A357 alloy. The research shows that best treating process is solution at 548oC×12 h, and aging at 175oC×6 h. After the heat treatment, the tensile strength and the elongation of A357 alloy can be improved by 2.1%and 29% by adding Y.