Modification of Hypereutectic Al-20%Si Alloy by Neodymium

Abstract

The modification mechanism was studied by OM, SEM, XRD and Trace Element Analysis. The results of OM and SEM analysis show that pure Nd can effectively refine primary and eutectic silicon in hypereutectic Al-20%Si alloy. Morphology of primary silicon is transformed from pentalpha to block and the average grain size of primary silicon is reduced from 80~120μm to 20~50μm after modification. Trace Element Analysis results show that Nd can purity base metal and reduce impurity contents. XRD patterns show that no new phase formed after Nd modification. The results of mechanical properties test show that whole properties of modified sample are significantly improved. Tensile strength increases about 35.8% from 117 MPa to 148 MPa after modification, Elongation change increases about 193% from 0.56% to 1.64%. The improvement of mechanical properties should be attributed to fine primary Si phase and eutectic silicon phase and purification of base metal after modification.