Crystallization Conditions for Ingots of High-Strength Aluminum Alloys with an Increased Content of Zirconium

The structure of model alloys of the aluminum–zirconium system and industrial grade 1973 alloy with an increased content of zirconium has been studied after rapid cooling to temperatures of the liquid–solid region and isothermal holding at these temperatures. It is shown that, during primary crystallization of intermetallic precipitates with a low crystallization rate, it is reasonable to use the model of decomposition of supersaturated solid solutions. It is found that the formation of Al3Zr particles results in a decrease of zirconium in the solid solution in the center of a grain and at its boundary. Under certain crystallization conditions, there is an incubation period for the precipitation of zirconium intermetallic compounds. It is shown that the incubation period for aluminum with 0.25 wt % zirconium is more than 2 min, and for 0.5 wt % zirconium, it is less than 0.5 min. The value of the dendritic parameter of the grade 1973 alloy with an increased content of zirconium during two-stage crystallization corresponds to the known pattern of the change in the dendritic parameter as a function of the cooling rate. Casting of ingots of the grade 1960 alloy with 0.27 wt % Zr by the two-stage cooling with the use of a water-cooling tray has been tested. This made possible to obtain ingots 84 mm in diameter without the formation of primary intermetallic compounds. The mechanical properties of forgings of such ingots exhibited an increase in ductility by 20% while maintaining the strength characteristics.