THE STRUCTURE OF NODULAR AND VERMICULAR G RAPHITE IN ALUMINUM-SILICONCAST-IRON STUDIED WITH SECONDARY-ELECTRON MICROSCOPY AND X-RAY MICROPROBE ANALYSIS

SEM and EDS studies on spheroidized aluminium-silicon cast iron have s hown the formation of ferrous alloy in interstitial regions of the pol ycrystalline precipitates of nodular graphite. This alloy is enriched with aluminium and rare earth elements. Thus the nodular graphite can grow in Al-rich surroundings. The growth process is probably associate d with the adsorption of atoms of rare-earth elements at certain cryst allographic planes of graphite (i.e. {10 (1) over bar 0}) since rare-e arth elements were found only in the nodular graphite and not in vermi cular graphite. A significant enrichment of nodular and vermicular gra phite with Al and Si. which may result from a segregation from the mat rix towards the interfacial surfaces, is not observed.