Zn-Al alloy excellent in elongation and method for producing the same

Abstract

A Zn—Al alloy excellent in elongation, and a method for producing the same are provided. The Zn—Al alloy comprises Zn in a range of 68 to 88% by mass and the remainder including Al and unavoidable impurities, and has a structure with β phases finely dispersed in respective α phases or respective α′ phases, not more than 5 μm in average grain size, a macrosegregation value of Al in the structure being less than 3%, wherein lamellar structures at a central part of the structure is at not higher than 30% by volume, and a difference in average hardness between the central part and a surface layer zone of the structure is not more than 15%, so that the Zn—Al alloy is improved in respect of elongation and uniformity.

1 . A Zn—Al alloy excellent in elongation, comprising: 
 Zn in a range of 68 to 88% by mass; and    the remainder including Al and unavoidable impurities, the Zn—Al alloy having a structure with β phases finely dispersed in respective α phases or respective α′ phases, not more than 5 μm in average grain size, a macrosegregation value of Al in the structure being less than 3.0%,    wherein lamellar structures at a central part of the structure is not higher than 30% by volume, and a difference in average hardness between the central part and a surface layer zone of the structure is not more than 15%.    
   
   
       2 . The Zn—Al alloy excellent in elongation according to  claim 1 , wherein an interval between the respective lamellar structures adjacent to each other is not more than 1000 nm.  
   
   
       3 . The Zn—Al alloy excellent in elongation according to claims  1  or  2 , wherein a maximum diameter of each of inclusions in the structure is not more than 50 μm in terms of the equivalent of a circle diameter, and pores not less than 0.5 mm in diameter in terms of the equivalent of a circle diameter are not present.  
   
   
       4 . A method of producing a Zn—Al alloy excellent in elongation by pouring molten metal of the Zn—Al alloy comprising Zn in a range of 68 to 88% by mass, and the remainder including Al and unavoidable impurities, into an ingot mold, the method comprising processes for: 
 casting while shielding poured molten metal from an external atmosphere;    cooling an ingot mold after the casting in a temperature range of 425 to 375° C. at an average cooling rate of not less than 1.0° C./sec, and subsequently cooling the ingot mold in a temperature range of 275 to 250° C. at an average cooling rate of not less than 0.08° C./sec;    a reheating process for reheating the ingot so as to be heated up and held at not lower than 350° C. before being quenched at an average cooling rate of not less than 0.5° C./sec; and    a warm working process for executing warm working at a temperature not higher than 275° C., and at an extrusion ratio not less than 4.