The High-Temperature Strength and Structure of the Al-Zn Binary Alloys

Abstract

Al-alloys with various concentrations of Zinc were prepared for the study of the creep phenomena at 200°C and 250°C under an initial stress of 2kg/mmmm².
The high-temperature strengh increased with the increase of Zinc concentration in the range of solid solution and the tendency was more remarkable in the dilute alloys. In the alloys containing Zinc beyond the solid solubility, the high-temperature strength reached maximum at the critical composition, and then decreased with increasing Zinc concentration in the range above the critical composition. The strength of two-phase alloys were found to be much higher than that of solid solution alloys.
The high-temperature strength was affected by the structure obtained during the heat-treatment before testing. It was strongly influenced by the size, shape and distribution of precipitates.The specimens containing smaller particles were stronger and the specimens with lameller precipitates produced by a boundary reaction, as shown in the 32.26wt% Zinc alloy, were also very stong. Ductile rupture was found to occur in the solid solution alloys, but brittle rupture in the two-phase alloys.
Grain boundary sliding, slip in grain and fold formation were observed on the surface of ruptured specimens. Cavities were found only at the triple point of boundaries on the brittleruptured specimens. The nucleation and development of cavities was confirmed to occur as the consequence of grain boundary sliding.