Superplastic zinc and aluminium alloys - which are heat-treated cooled, worked pref rolled pref during phase-transformation and cooled

摘要

alloys of Parent Patent, are rendered superplastic by (a) heat-treatment of an article of alloy contg. 18-40 wt.% Al, bal. Zn with eventual contaminants and small quantities of ternary alloying elements, and where alloy compsn. and temp. are such that mono-phase condition of Zn-Al phase-diagram is maintained until a homogenous structure is reached; (b) cooling to 275 degrees C at =10 degrees C/min.; and (c) working to reduce dimensions by =90%, whre total %-age reduction of measurements is carried out at =200 degrees C. In present specification, alloy article is cooled initially to =275 degrees C and then further cooled, after working at least in part. Over half of total %-age dimensional reduction is effected at =275 degrees C, pref. during phase-change taking place at 275 degrees C. Method is esp. for sheets for vacuum deformation. Formation of surface defects, and esp. of edge fractures, is reduced or prevented.