| A study of hydrogen effects was conducted on 99.999% pure aluminum. Hydrogen was introduced into the material by means of a corrosion process. Two corrosive media were used; deionized pure water and an alkaline solution. The former was used for dynamic hydrogen charging during mechanical tests and the latter for hydrogen precharging. The corrosion reaction in the dynamic charging was intensified by application of weak ultrasonic oscillations.;It was found that hydrogen changed the response of the material to plastic deformation causing softening and plastic deformation localization on the macroscale and slip line coarsening as well as an increase in their waviness on the microscale. Hydrogen did not cause an earlier onset of the macroscopic plastic instability, i.e. necking.;Hydrogen modified the fracture mode, changing it from a totally ductile, chisel point type to a more brittle transgranular or intergranular fracture. The fracture started only after the onset of necking. The hydrogen induced fracture modification is believed to result from the plastic deformation modification and from the effect of hydrogen on microvoid nucleation. Some fracture surfaces were covered with a film, that was occasionally fragmented by a network of cracks ("mud crack pattern"). This phenomenon is believed to be a post fracture effect caused by adhesive wear between opposite fracture surfaces.;Hydrogen charging resulted in the formation of bulk vacancy clusters, a linear dimensions shrinkage and grain growth. This was interpreted as evidence for vacancy production during the corrosion reaction and for a significant hydrogen-vacancy binding enthalpy. |
