亜包晶Ａｌ‐Ｚｒ合金の時効析出に対するＦｅ，Ｓｉの少量添加の影響

Abstract

Hardening and precipitation during aging of subperitectic Al-Zr alloys containing about 0.1%Fe or Si were studied in comparison with a binary Al-0.22%Zr alloy. The specimens were homogenized at 650°C for 8hr and quenched in ice brine, and then aged at 350°C, 400°C and 450°C for periods ranging from 5hr to 104hr. Changes in hardness and electrical resistivity during aging were measured by a microvickers tester and by the standard potentiometric method. Changes in microstructure were also observed by means of optical and transmission electron microscopy.The maximum hardnesses were obtained after prolonged aging of 103104hr at 350°C. A small addition of Si accelerated the hardening of the alloy remarkably, but an addition of Fe did not effect the age hardening rate.There were two-step reactions in the resistivity-aging time curves of Al-Zr and Al-Zr-Fe alloys. It is thought that the first reaction corresponds to the precipitation due to grain boundary reaction and the second to continuous precipitation within the grain. The area fraction of the former was about 3 percent at most in Al-Zr-Fe alloy and nearly zero in Al-Zr-Si alloy. Coherent spherical precipitates were uniformly distributed within the grains. It is concluded that the precipitates are a predominant factor for the increment of hardness during aging. Platelike precipitates were also found in the three kinds of specimens, especially in an Al-Zr-Fe alloy. The remarkable acceleration of age hardening by a small addition of Si seems to be the acceleration of nucleation of the spherical particles within the grains due to Si atoms.