Influences of hydrogen on deformation and fracture behaviors of high Zn 7XXX aluminum alloys

Abstract

Hydrogen degrades the mechanical properties of high strength 7XXX aluminum alloys in two ways: (i) degrades the mechanical properties by hydrogen embrittlement, and (ii) partitioned into micropores as molecular hydrogen and make contributions to ordinary ductile fracture. The multifaceted effects of hydrogen on the mechanical properties of high Zn content 7XXX aluminum alloys during deformation and fracture is studied by using synchrotron X-ray microtomography. Our results have revealed that the hydrogen susceptibility has increased with increasing the Zn amount. High concentration of hydrogen was induced by the EDM wire eroder. This high concentrated hydrogen induces quasi-cleavage fracture and restricts the growth of 2 micropores during ductile deformation. The threshold concentration of hydrogen ahead of the crack tip for the nucleation of quasi-cleavage feature was estimated to be 13 cm 3 /100 g Al.

Hydrogen-accelerated spontaneous microcracking in high-strength aluminium alloys

“…We confirmed the hydrogen content of the alloy using the vacuum fusion method with EDM, finding that it increased from 0.14 to 6.97 mass ppm in water purified by ion exchange resins 31 . The hydrogen content in the prepared Al-Zn-Mg alloys after EDM cutting by a gas chromatography-type thermal desorption analyser (PDHA-1000, NISSHA FIS, Inc.) was 6.98 mass ppm, which is almost the same as that found elsewhere (6.97 mass ppm) 11 . The hydrogen in specimens after EDM was presumed to be highly concentrated on the surface region.…”

“…Researchers have been working on a number of efforts to reduce the hydrogen concentration as a way to prevent HE 10 , as the presence of a supersaturated hydrogen concentration in practical use generally enhances ductile fracture due to the high-density micropore distribution. More recently, however, a small portion of dissolved hydrogen has been found to cause an anomalous brittle fracture known as "quasi-cleavage" fracture 11,12 .…”

Ultrasonic-Assisted Laser Metal Deposition of the Al 4047Alloy

“…Certain studies have shown that the formation of residual pores is related to stress concentration, which guarantees worse mechanical performance of the deposited metal [11,12]. Therefore, it is necessary to study the influence of the processing parameters on the defects of insufficient densification.…”

Local Deformation and Fracture Behavior of High-Strength Aluminum Alloys Under Hydrogen Influence

“…Kuramoto et al reported that the true fracture strain of Al-4.9Zn-2.2Mg-1.3Cu alloy is approximately 17% at a strain rate of 1.67 × 10 -4 s -1 but decreases to less than 5% at a strain rate of 1.67 × 10 -7 s -1 in air [8] . Although SSRT is not employed, the HE of Al-Zn-Mg(-Cu) alloys is observed in tensile tests at strain rates of 10 -4 to 10 -3 s -1 when the tensile loading is periodically held [9] . When the holding time is longer, the embrittlement is more prominent.…”