Modification effect of pure rare earth metal La on as-cast hypereutectic Al-17%Si alloys
(State Key Laboratory of Metal Matrix Composites,
Shanghai Jiaotong University, Shanghai 200030, China)
Shanghai Jiaotong University, Shanghai 200030, China)
Abstract: The modification effect of La addition on the microstructural characteristics of hypereutectic Al-17%Si alloys was studied. Microstructures were examined using conventional optical microscopy and electron probe X-ray microanalyzer. The morphology of Si crystal was evaluated by quantitative metallographical analysis. The results indicate that simultaneous modification to both primary and eutectic Si crystals is obtained by the addition of pure rare earth metal La in the hypereutectic Al-17%Si alloys while the optimal effect of La is obtained at a rather large scale. La begins to form intermetallic compound when its concentration exceeds approximately 1%, which appears as dark platelets in etched specimens. Electron probe X-ray microanalysis experiment shows that La-rich platelet could be represented as Al1Si2La2 consisting of LaSi2 and some unknown ternary AlxSiyLa phase.
Key words: hypereutectic Al-Si alloy; casting; La; modification