Zn-Al Alloy Having Excellent High-Speed Deformation Properties and Process For Producing the Same

Abstract

A Zn—Al alloy excellent in static deformability as well as dynamic deformability and applicable to large-sized structures, and a method for production thereof. The alloy contains 30-99% Zn, with the remainder being Al and inevitable impurities, and has a metallographic structure in which the α phase or α′ phase having an average grain size no larger than 5 μm contains the β phase finely dispersed therein, the Al inclusions have a maximum equivalent circle diameter no larger than 50 μm and are free of pores no smaller than 0.5 mm in terms of equivalent circle diameter, and the macrosegregation of Al is less than 3.0% and the microsegregation of Al is less than 2.0%. (% means mass %.)

1 . A Zn—Al alloy excellent in rapid deformation properties containing 30 to 99% Zn, with the remainder being Al and inevitable impurities, which has a metallographic structure in which the α phase or α′ phase contains the β phase dispersed therein, the α phase or α′ phase has an average grain size no larger than 5 μm, the Al inclusions have a maximum equivalent circle diameter no larger than 50 μm and are free of pores no smaller than 0.5 mm in terms of equivalent circle diameter, and the macrosegregation of Al is less than 3.0% and the microsegregation of Al is less than 2.0%. (% means mass %.) 
     
     
         2 . The Zn—Al alloy excellent in rapid deformation properties as defined in  claim 1 , wherein the β phase has an average grain size no larger than 3 μm, preferably no larger than 0.1 μm. 
     
     
         3 . A method for producing a Zn—Al alloy excellent in rapid deformation properties, which comprises:
 a step of casting a molten Zn—Al alloy into a mold while isolating the melt from the ambient atmosphere,   a step of cooling the mold after casting at an average cooling rate no lower than 0.25° C./s in the temperature range from 425 to 375° C. and no lower than 0.020° C./s in the temperature range from 275 to 250° C.,   a step of reheating which includes keeping hot at 350° C. or above and subsequent quenching,   a step of blooming at 275° C. or below, and   a step of warm working at 275° C. or below.