Low Temperature Age-Hardening of Al-12mass % Zn-0.5mass % Cu Alloy

Effect of addition of a small amount of copper to Al- 12mass % Zn binary alloy on the process of low temperature aging is studied by hardness test and transmission electron microscopy. Age hardening rate after quenching from various temperatures is slowed down by addition of 0.5mass % copper to the binary alloy. The hardness obtained after long aging, however, is increased a little by the addition of copper. The extent of soft surface layer formed by aging in the copper-added alloy is nearly equal to that obtained in the binary alloy

Precipitation Hardening and Effect of Surface Layer on the Fatigue Strength of an Al-1.2mass% Si Alloy

Dependence of precipitation hardening on the distance from specimen surface and effect of the surface layer on the fatigue strength of an Al-1.2mass% Si alloy were studied by microhardness test, transmission electron microscopy and repeated tension fatigue test. Rate of age-hardening was slower in the vicinity of surface than in the interior of the specimen aged at 423K after quenching from 853K. The result of the electron microscopy was that the size ot Si precipitates formed in the vicinity of surface was smaller than in the interior of specimen aged for 6ks at 423K. This difference was considered to be caused by the effect of the surface as vacancy sinks which slowed down the growh of Si precipitates in the vicinity of the specimen surface. A specimen surface layer whose hardness was different from that of the specimen interior was formed at the vicinity of the surface when the specimen was aged at relatively low temperature such as 423K. The fatigue strength in repeated tensile test ot the specimen did not depend on whether the specimen surface layer was present or not

AL 12MASS% ZN ゴウキン ノ ヒロウ キョウド ニ オヨボス ビリョウ CU テンカ ノ エイキョウ

The fatigue strength under repetitive tensile stress and the age-hardening process were examined in the case of a small addition of copper to the Al-12mass%Zn alloy. The results obtained are summarized as follows. (1) In isothermal age-hardening curve the stationary hardness value of copperadded alloy was a little higher than that of the binary alloy, but the time to reach the value was longer. (2) A small addition of a copper did not alter the thickness of the soft surface layer. (3) A small addition of copper did not alter the fatigue strength. Accordingly the existence of the soft surface layer is considered to increase the fatigue strength of the copper-added alloy, too

AL 12MASS% ZN 0.5MASS% FE ゴウキン ノ テイオン ジコウ コウカ

The age hardening process, formation of soft surface layer and fatigue strength of Al-12mass%Zn-0.5mass%Fe alloy were studied by measurements of microhardness and number of cycles to failure under repeated tensile loading. The results obtained are summarized as follows. (1) In Fe-added alloys, the rate of hardening is smaller than in binary allay and the degree of hardening is small even after aging for a long time. (2) An addition of Fe promotes the formation of soft surface layer in binary alloy. (3) An addition of Fe has an effect of rasing the fatigue strength to repetitive tensile loading in binary alloy