Inclusions and hydrogen and their effects on the quality of direct chill cast and flat rolled aluminium alloys for aerospace applications

Gerrard, Alexander James (2014). Inclusions and hydrogen and their effects on the quality of direct chill cast and flat rolled aluminium alloys for aerospace applications. University of Birmingham. Eng.D.

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Abstract

Flat rolled Al alloys manufactured using the Direct Chill casting process are used in safety critical applications and therefore need to be of the highest possible quality. Liquid metal is cleaned using a mixture of inert Ar and reactive Cl gases before casting.

The first section of this work explores the aetiology of defects in hot rolled Al plate, found using ultrasound. Inclusions extracted from 7xxx plate were examined using scanning electron microscopy. A second type of defect found in 7475 alloy plate was established to be a coarse grain structure.

The second section aimed to provide a better understanding of the role of Cl on degassing. The effects of Cl on the degassing performance of a Spinning Nozzle Inert Floatation degassing unit were approached statistically using ALSCAN. Finally, 20 kg melts of Al and Al alloys were doped with H and subsequently degassed, and the reduction in H over time was measured using ALSPEKH.

In the third section the LECO H determination device was used to degas Al specimens to very low levels. Degassed specimens were melted under air or N\(_2\) atmosphere, so that when cracks formed in the surface oxide layer either Al\(_2\)O\(_3\) or AlN formed. After subsequent exposure to pure H\(_2\) gas the specimens that formed AlN were found to have absorbed more H than those heated in air.

Type of Work:

Thesis (Doctorates > Eng.D.)

Award Type:

Doctorates > Eng.D.

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