Mechanical properties and 95 degrees C aging characteristics of zircon-reinforced Zn-4Al-3Cu alloy

A process for preparing zinc alloy castings containing dispersions of zircon particles is described. Composites were prepared by stirring zircon particles in Zn-4Al-3Cu (ZAS) alloy melts and subsequently casting these melts in permanent molds. It was found that additions of zircon resulted in an increase in the sliding wear resistance and in the proportional limit in compression. The aging characteristics of the ZAS alloy have also been investigated by hardness tests, dilatometry technique, and transmission electron microscopy observations. There are two kinds of precipitates that occur during the aging process. The alpha-phase precipitates from the eta phase in the early stage of aging and the copper-rich epsilon-phase precipitates from the eta phase in the later stage of aging. Therefore, there are two peaks in the hardening curve caused by both alpha-phase and epsilon-phase precipitation. The alpha-phase precipitation induces the dimensional shrinkage, and the copper-rich epsilon phase precipitation results in dimensional expansion. Zircon particles existing in ZAS alloy reduce the maximum shrinkage from 353 X 10(-6) for the monolith to 167 x 10(-6) for the composite. Two groups of parallel alpha-phase plates had formed within the eta dendrite during aging at 95 degrees C. The orientation relationship between the alpha phase and matrix was determined as [(1) over bar 101](<eta)>//[l (1) over bar 0](alphaalpha), (11 (2) over bar 0)(eta)//(111)(alpha).