High-aluminium zinc alloy (ZnAl27Cu2) modified with titanium and boron

The paper presents the results of investigations concerning the influence of the titanium-boron modifier quantity on the structure and mechanical properties of ZnAl27Cu2 alloy. The modification has been performed with the use of AlTi5B1 master alloy, thus introducing into the molten alloy 0.015%Ti and 0.003%B; 0.025%Ti and 0.005%B; 0.035%Ti and 0.007%B and eventually 0.045%Ti and 0.009%B. Samples for examination have been cast in sand moulds. The optimum mechanical properties Rm=440MPa and A5=8% have been achieved by introducing 0.035% Ti and 0.007% B into the alloy. It has been found that morphological changes of the primary crystals of α solid solution take place due to the modification. The dendrites with widely outspread arms take the shape of rounded, globular crystals. The size of α phase crystals decreases, but to the rather small degree, proportionally to the quantity of added modifier.