SOLIDIFICATION AND FOUNDRY STUDIES OF ZN-AL ALLOYS

It is well known that the commercial Zn/Al alloys, particularly the Zn-11%Al and Zn-27%Al alloys, segregate markedly during founding and also that an “inverted pipe” is commonly present. A detailed study of the solidification of 8, 11 and 27% aluminum alloys has been carried-out to investigate the manner of an extent to which segregation arises in order to develop better foundry procedures to exploit the considerable potential of these alloys. This work has involved the uni-directional solidification of many samples under a wide variety of conditions selected to exploit naturally-induced and forced fluid flow in the melt. The results of this work are being applied to develop various foundry procedures aimed at the production of sound homogeneous castings. Since it is possible to eliminate the major foundry problem with these alloys, namely, underside shrinkage, in the case of the Zn-8%Al and Zn-11%Al by adjusting such casting variables as pouring temperature, mold type and riser volume and placement, discussion of the results will be confined to the Zn-27%Al alloys. This alloy type displays the greatest mechanical strength and is most prone to underside shrinkage in “chunky” castings.