Search

The internal microstructures of Ni–P-plated Al–Zn–Mg-based alloys were investigated using synchrotron X-ray computed tomography, together with various analytical methods for hydrogen detection. We clarified that hydrogen-induced pores were generated and segregated near the top and bottom surfaces of a rolled sheet of a commercial-purity Al–Zn–Mg-based alloy with Ni–P plating. In contrast, such segregation of hydrogen micropores was not observed in the high-purity-grade Al–Zn–Mg alloys with Ni–P plating. This result suggests that hydrogen enters the Ni–P plating layer during the plating operation and generates pores in the surface region owing to surface inclusions. Additionally, the hydrogen-induced defects deteriorated the tensile properties such as tensile strength and elongation of the commercial-purity Al–Zn–Mg-based alloys containing higher levels of impurities such as Fe and Si with Ni–P plating. [Display omitted] • Internal microstructures of Ni–P-plated Al–Zn–Mg-based alloys investigated. • Synchrotron X-ray computed tomography and hydrogen detection methods were employed. • H enters plating layer and generates surface micropores due to surface inclusions. • H-induced defects deteriorate the tensile properties of the plated pure alloy. [ABSTRACT FROM AUTHOR]

In this study, a novel analytical system was developed to monitor the environmental hydrogen embrittlement of Al-Zn-Mg-based aluminum alloys dynamically and quantitatively under atmospheric air pressure. The system involves gas chromatography using a SnO 2 -based semiconductor hydrogen sensor, a digital image correlation step, and the use of a slow strain rate testing machine. Use of this system revealed that hydrogen atoms are generated during the plastic deformation of Al-Zn-Mg alloys caused by the chemical reaction between the water vapor in air and the alloy surface without oxide films. Digital image correlation also clarified that the generated hydrogen atoms caused numerous localized grain boundary cracks on the specimen surface, resulting in a localized grain boundary fracture. The amount of hydrogen atoms evolved from the embrittled fracture surface was 2.7 times as high as that from the surface without embrittlement. [Display omitted] [ABSTRACT FROM AUTHOR]