The combined effect of corrosive media and its temperature on the fatigue performance of AA5086-H321 weld joints

Abstract

This work investigates the fatigue behavior and damage mechanisms in the friction stir weld joints of AA-5086-H321 alloy under the combined effect of media: 3.5 % NaCl and air and its temperature: 24°C and ∼0°C. Sinusoidal loading tests were performed at different load ratios: 0.1 and 0.5, in load-controlled mode at 1 Hz in 3.5 % NaCl. The fatigue lives of the weld joints deteriorated notably under 3.5 % NaCl by selectively attacking its vulnerable nugget zone and heat-affected zone, while the effect of low temperature (∼0°C) was beneficial in both air and 3.5 % NaCl. Two types of crack initiation mechanisms were identified irrespective of the other test conditions: pit-to-pit type, favored at low-stress amplitudes, and pit-to-crack type, favored at high-stress amplitudes. A few cases of crystallographic corrosion pitting were also observed and were accredited to the inherited crystal defects within the Al-matrix. The effect of surrounding temperature was apparent on the crack growth mechanism with limited or no impact on the crack initiation mechanism. The fatigue cracks grew in the intergranular mode under 3.5 % NaCl, while its quantitative presence was decreased at ∼0°C, irrespective of the media, which was attributed as one of the key factors for the increased fatigue performance at ∼0°C.