Effects of the 3rd additional elements on grain size of primary silicon and its cooling rate dependency in Al-20%Si alloy

Abstract

Grain size of primary silicon and its cooling rate dependency were first studied on hyper eutectic Al-20%Si alloy which had been prepared with various mold materials. Then, the effects of single addition (about 0.2at.%) of about 30 sorts of the 3rd elements on the grain size of primary silicon and its cooling rate dependency were fully examined on wedge-shaped samples cast with pure copper mold. The effects of the addition amounts of effective elements and the double addtion of the said elements were also studied.The main results obtained were as follows:(1) The grain size of primary silicon was expressed by almost hyperbolic relation with the cooling rate. When the cooling rate was in the range of higher than 20°C/sec, the grain size and its cooling rate dependency decreased; but, they sharply increased in the range of lower than 10°C/sec.(2) Relating to the cooling rate dependency, Li, Na, Cd, B, Sn, Pb, V, Sb, Te, Ni, and rate earths (Larich) showed almost the same tendency as the case of no addition; Cu, Ag, Zn, In, Ti, Zr, Bi, and Mn showed the tendency of larger cooling rate dependency; while, Be, Mg, Ca, P, Cr, Se, and rare earths (Ce-rich) showed the tendency of smaller cooling rate dependency.(3) The most effective element for the decrease of cooling rate dependency was found to be phosphorus. The double addition of more effective elements was not so effective as the single addition of phosphorus.(4) Most elements, giving the decrease of cooling rate dependency also gave the decrease of grain size.(5) Eutectic matrices of these alloys were improved in all cases, except the additions of Cu, Ag, Be, Sn, Pb, V, P, and Mn.