An Investigation On Modification Of Zinc-aluminum Alloy Used For Die Casting

In this paper, the complex modification processes of the Al-5Ti-B intermediate alloy and K2TiF6+KBF4salt-mixture for ZnA14alloy and ZnA14Cul alloy were investigated. The characterization of the microstructure and qualitative analysis were conducted by using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer (EDS). Properties of the studied alloy such as hardness, tensile strength, impact toughness and fluidity were tested in detail. The effects of adding different amounts of modificators on the characterization of the microstructure and properties were discussed. And the modification mechanism and the influencing factors on the fluidity of zinc-aluminium alloy were also analysised. The conclusions can be drawn from the studies as the follows:1) Al-5Ti-B intermediate alloy can effectively refine grain of ZnA14alloy and ZnA14Cul alloy, reduce the amount of dendrites, shorten the tissue slice layer spacing between the intercellular layers of the dendrite network. Containing Al3Ti and TiB2particles, Al-5Ti-B intermediate alloy can act as heterogeneous nucleation of a-Al phase effectively, promote a-Al to grow up, and finally inhibit the growth of large η-Zn phase. Both the refining effect and the comprehensive mechanical performance become optimum, when the content of Al-5Ti-B is0.6%for ZnA14and1.0%for ZnA14Cul alloy respectively.2) When the metamorphic temperature is below750℃, the addition of salt-mixture K2TiF6+KBF4with the mass ratio of4:1to ZnA14Cul alloy, can effectively refine ZnA14alloy and ZnA14Cul alloy dendrite, change the dendrite morphology, shorten the tissue slice layer spacing between the intercellular layers of the dendrite network. This is because under this condition, the metamorphic system can form Al3Ti particles, and successfully refine dendrites. Both the refining effect and the mechanical properties including brinell hardness, tensile strength, elongation and impact toughness are optimized, when the amount of the modificator is0.8%for ZnA14and0.7%for ZnAl4Cul alloy respectively.3) Al-5Ti-B can effectively improve the fluidity of ZnAl4Cul alloy. When the content of Al-5Ti-B is1.0wt%, the fluidity becomes best. Adding salt-mixture modificator can lead to the increase of impurities in the alloy when smelting, and consequently making the fluidity of the experimental alloy worse. It shows in zinc-aluminum binary alloy, the smaller the interval between solid and liquid line is, the better the fluidity is. In addition, the high pouring temperature and the fine crystal grain contribute to the improvement of the fluidity.