Investigation of fatigue behaviour of zinc-aluminum based alloys in different environments

SUMMARY Investigation of Fatigue Behavior of Zinc- Aluminum Based Alloys In Different Environments A series of binary zinc-aluminum and ternary zinc-aluminum-copper alloys were produced by permanent mould casting. Two of the ternary alloys were heat-treated by aging at 100°C. The microstructure of the alloys was examined using optical and electron metalography. Hardness, tensile strength and total elongation of the alloys were determined by hardness measurements and tensile testing. Fatigue properties of the alloys were investigated in air, salt water (3.5% NaCl solution) and acid solution (1% HC1) using a rotating beam fatigue machine which was designed and built for this work. As a result of this work the effect of chemical composition and corrosive environments on the fatigue behavior of the alloys was determined. The fatigue strength and fatigue life of the zinc-aluminum alloys were found to be very sensitive to corrosive environments. However the acid solution was found to be more effective on the fatigue behavior of the alloys than the salt water. The highest fatigue strength was obtained with the ZnA140Cu2 alloy while the binary ZnA120 alloy exhibited the lowest fatigue strength among the alloys in air. The fatigue strength and fatigue life of the alloys increased with increasing aluminum content in air, but in corrosive environments they decreased with increasing aluminum content. It was also found that addition of copper up to 2% increased the fatigue strength and fatigue life of the ZnA140 alloy in air. However, above this level fatigue strength of the ternary alloys decreased with increasing copper content. On the other hand, the copper addition had a little effect on the fatigue behavior of the alloys in corrosive environments. Although the heat treatment increased the hardness and tensile strength of the ternary alloys greatly, it was found to be not effective on the fatigue behavior of them. The relationships between the fatigue properties and chemical composition of the alloys were found to be expressed by linear equations. It was also found that Basquin's law can be used to express the fatigue behavior of the zinc-aluminum alloys in the environments used. Key Words: Zinc-Aluminum Alloys, Fatigue Behavior, Fatigue Life, Corrosion Fatigue, Basquin's Law. VI