INFLUENCE OF SR CONTENT ON THE MODIFICATION OF SI PARTICLES IN AL-SI ALLOYS

The effects of Sr concentration on the Si particle structure in modifi ed A356 alloys have been investigated. Experiments have been conducted for Sr contents ranging from 0.005 to 0.5 %. Data have been acquired for two different values of secondary dendrite arm spacing. The castin gs have been analyzed by optical and scanning electron microscopy. The results indicate that Sr concentrations less than about 0.015 to 0.02 %, lead to a refinement of the Si crystals. At Sr concentrations grea ter than about 0.02 %, a coarsening of the Si particles is observed. T wo types of Sr containing intermetallic particles may form at Sr conce ntrations greater than about 0.03 %.