Formation behaviour of blister in cast aluminium alloy

Abstract

The formation behaviour of a blister in a die cast aluminium alloy was observed by employing a combined methodology of in situ three-dimensional observation using X-ray microtomography and image based simulation. It has been revealed, via a reverse approach based on the simulation, that nitrogen and carbon dioxide gases fill the blister nucleus. Spontaneous growth of the blister nucleus occurs through creep deformation of the surrounding aluminium due to the blister nucleus' high internal gas pressure. This internal gas pressure also induces hydrogen precipitation in the form of micropores, which undergo steady growth in a spherical shell region around the blister nucleus. The selective growth of the micropores is attributable to the elevation of hydrostatic stress in directions parallel to the casting surface, thereby promoting the expansion of the blister, also parallel to the casting surface, through the absorption of surrounding micropores into the blister nucleus.

Influence of intermetallic particles on the initiation and growth behavior of hydrogen micropores during high-temperature exposure in Al-Zn-Mg-Cu aluminum alloys

“…2a). Closely spaced hydrogen micropores are prone to form larger pores through coalescence partly due to the superposition of hydrostatic strain fields among neighboring pores [22]. In contrast, almost no coalescence of neighboring hydrogen micropores is observed for those nucleated on the tips of Al 2 CuMg/Al 7 Cu 2 Fe particles, as shown on particle A in Fig.…”

“…where P is the internal gas pressure, γ is the surface tension of aluminum and d is the diameter of a pore. The internal gas pressure of a typical hydrogen micro pore (1 μm) is approximately 4 MPa under the assumption of γ = 1.16 N m -1 [22]. Therefore, it can be inferred that the growth of hydrogen micropores under high temperatures is induced by the creep deformation of the surrounding aluminum matrix caused by the high internal gas pressure [13,22].…”

“…The internal gas pressure of a typical hydrogen micro pore (1 μm) is approximately 4 MPa under the assumption of γ = 1.16 N m -1 [22]. Therefore, it can be inferred that the growth of hydrogen micropores under high temperatures is induced by the creep deformation of the surrounding aluminum matrix caused by the high internal gas pressure [13,22]. Kawabata, et In conclusion, our investigations using high-resolution X-ray tomography have revealed the influence of intermetallic particles on the initiation and growth of hydrogen micropores at high temperatures in the Al-Zn-Mg-Cu aluminum alloys.…”

Effect of hydrogen on the integrity of aluminium–oxide interface at elevated temperatures

“…Previous works have shown that in hydrogenated metals, blisters usually grow with increasing temperature 14 23 24 25 . However, occasionally they could also shrink or disappear 26 27 .…”

“…However, occasionally they could also shrink or disappear 26 27 . The accelerated blister growth is often interpreted as simply due to the rise of internal gas pressure in the hydrogen-filled cavities 24 25 , while the reason for shrinkage is still elusive. However, there are other important factors that can instigate and mediate blistering but have not been taken into consideration fully.…”