Effect of Hydrogen on the Mechnical Properties and Fracture Behavior of High Purity Aluminum

In this study of hydrogen effects on 99.999% pure aluminum, hydrogen was introduced by a corrosion process. Two corrosive media were used; deionized pure water was used for dynamic hydrogen charging during mechanical tests and an alkaline solution for hydrogen precharging. Hydrogen was found to change 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 from a totally ductile, chisel point type to a more brittle transgranular or intergranular fracture. Fracture started only after 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 which is believed to be a post fracture effect caused by adhesive wear between opposite fracture surfaces. Hydrogen charging resulted in formation of bulk vacancy clusters, linear dimensions shrinkage and grain growth which were interpreted as evidence for vacancy production during the corrosion reaction and for a significant hydrogen-vacancy binding enthalpy.