Modification of Al–7Si–0·3Mg alloy by sodium and strontium in presence of antimony

Abstract

Antimony exerts a degrading effect on the modification of Al–Si alloys with additions of either sodium or strontium, particularly at usual levels of either of the last two elements. The deleterious effect can be minimised if significantly higher levels of modifier are used. In each instance, antimony reacts with the modifier in the melt to form a dense solid compound which sinks to the bottom of the melt. Combinations of sodium and strontium used together are shown to provide beneficial long term modification when antimony is not present. In the presence of antimony these combinations can overcome its negative effect and once again provide long term modification. A modification treatment with 0·03%Sr and 0·01%Na is suggested for use with antimony levels of ≤ 0·01%. At 0·04%Sb, a treatment with 0·06%Sr and 0·02%Na is equally effective.

MST/925