Effects of Ti-FPB treatment on fatigue strength of FSWed aluminum alloy and on its mechanical properties in salt water environment

Abstract

This study was conducted to investigate the effects of titanium-fine- particle bombarding (Ti-FPB) treatment on fatigue strength of friction-stir-welded aluminum alloy (FSW material) and on its mechanical properties in salt water environment. Fatigue cracks of Ti-FPBed FSW material were initiated from the root of the overhung weld toes formed by the passing of the tool, as well as those of FSW material. Ti-FPB treatment introduced compressive residuals stress to the surface of FSW material, although its absolute value was relatively low near the weld toes. As a result, fatigue strength of FSW material was recovered by Ti-FPB treatment to the same level of the substrate. Ti-FPB treatment diffused titanium to the surface of FSW material. Diffusion of titanium was insufficient near the weld toes because of disturbance by the overhung weld toes. Such insufficient diffusion of titanium induced electrolytic corrosion. As a result, tensile strength of FSW material in salt water environment deteriorated with Ti-FPB treatment. © 2014 The Japan Institute of Metals and Materials.