Behavior of hydrogen in Al-Mg alloys investigated by means of hydrogen microprint technique

Abstract

In recent years, hydrogen has been attracting attention as a clean energy. For its transport, a tank for liquid hydrogen is necessary, and 5083 aluminum alloy has been chosen as a candidate of the tank material. On the other hand, hydrogen is thought to permeate most metallic materials from a corrosive environment, resulting in hydrogen embrittlement. In the actual liquid hydrogen tank, only one side of the inner sheet material is exposed to hydrogen gas. Although serious environmental embrittlement of aluminum alloys by molecular hydrogen has not been reported so far, the behavior of hydrogen has not been investigated in detail in this condition. In the present study, analysis on the permeation and migration behavior of hydrogen atoms in the above condition has been made by means of hydrogen microprint technique on a sheet of 5083 aluminum alloy, together with Al-4.5mass%Mg binary alloy which is a base material of the 5083 alloy. It was revealed that hydrogen atoms can invade and permeate aluminum alloys from the gaseous hydrogen atmosphere. The entrance site was thought to be the second phase particle and the fresh surface produced by the plastic deformation. Once hydrogen atoms entered the alloys, they were deduced to act in the same manner as impurity hydrogen atoms: migrate with gliding dislocations or by a short-circuit diffusion along dislocation lines, be transferred to grain boundaries or interphase boundaries and finally be evolved at slip lines, grain boundaries, and second phase particles on the surface.