The grain refinement of Al-Si casting alloys

When the technical information on the grain refining of aluminium-silicon casting alloys is reviewed, it becomes evident that today's practices are employed primarily for historical reasons. In particular, the high Ti levels(> 0.1%) in 356 and 357 alloys date from the years when modem Al-Ti-B grain refiners did not exist. This paper reviews the history of grain refining in Al-Si alloys and an improved practice is outlined. It is important to understand that titanium can be present in two forms. One dissolves in aluminum; the other is nearly insoluble. With today's powerful Al-Ti-B refiners, there is no reason for large additions of soluble titanium. Experimental data is presented for A356 alloy. Lowering the dissolved Ti levels has no deleterious effect and offers the potential of a significant cost saving.