Abstract
Soft surface layer formed after low temperature aging was studied on Al–12, 16, 18 and 20 mass%Zn alloy by means of hardness test and resistometry. The soft surface layer could not be observed in 20%Zn alloy aged at 273 K when the quenching temperature was higher than 673 K. The thickness of the soft surface layer in the specimen aged at 273 K after quenching from 673 K decreased with increase of Zn concentration. Aging curve in resistivity showed the depression of the growth of GP zones in the surface layer relative to the interior of the specimen. Fatigue strength in the repeated tensile mode was higher when the soft surface layer formed during aging was thicker. The soft surface layer formed by partial reversion treatment also increased fatigue strength.
