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The nature of hydrogen solutions in metals and the evidence for physical and chemical hydrogen traps are examined as a prerequisite for interpreting and evaluating experimental observations and information from manufacturing operations. The sources, distribution, control, and effects of hydrogen are then considered for the metals and alloys under review. For aluminium and its alloys, unsoundness in castings, mechanical weaknesses generated by hydrogen, and blistering in wrought products are discussed in terms of the redistribution of hydrogen which occurs in the metal as it solidifies during casting. The arguments are extended to the formation and distribution of microporosity in magnesium alloy castings, taking account of the more dominant role of solidification contraction. Reference is also made to effects of an entirely different character which occur with magnesium alloys containing elements which form stable hydrides. The effects in copper are reviewed with emphasis on interactions between hydrogen and other gas-forming elements, notably oxygen, which may also be present. The topics considered are the control of pitch in fire-refined tough-pitch copper, the evolution of gases in copper alloy castings, steam embrittlement of oxygen-bearing copper annealed in reducing atmospheres, and hydrogen blistering in some self-deoxidizing copper alloys in wrought form. The removal of hydrogen from liquid metals is an important element in controlling the effects described and so the various techniques available are described and evaluated where appropriate, including modern practices such as ‘in-line’ degassing for aluminium and its alloys.

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