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This paper aims to characterise the hardness, tensile properties, corrosion behaviour and fatigue properties (in air and in a 3.5 per cent NaCl solution) of aluminium 6061-T651 in the as-received and as-welded conditions.

Aluminium 6061-T651 plate material, prepared with double-V or square butt joint preparations was welded using semi-mechanised or mechanised pulsed gas metal arc welding. Magnesium-alloyed ER5356 or ER5183 filler material or silicon-alloyed ER4043 filler wire was used. The material was characterised in the as-supplied and as-welded conditions, and fatigue tests were performed in air and in a 3.5 per cent NaCl solution. The fatigue results were compared to the reference fatigue design curves for aluminium published in Eurocode 9 – Part 1-3.

Significant softening, attributed to the partial dissolution and coarsening of precipitates, grain growth and recrystallisation during welding, was observed in the heat-affected zone (HAZ) of the 6061-T651 welds. During tensile testing, failure occurred in the HAZ of all 6061 welds tested. Welding reduced the room temperature fatigue life of all specimens evaluated. In 6061 welds, failure occurred preferentially in the softened HAZ of the welds. The presence of a corrosive environment (a 3.5 per cent NaCl solution in this investigation) during fatigue testing reduced the fatigue properties of all the samples tested. Corrosion pits formed preferentially at second phase particles and reduced the overall fatigue life by accelerating fatigue crack initiation.

The fatigue properties of welded aluminium structures under dynamic loading conditions have been studied extensively. Welding is known to create tensile residual stresses, to promote grain growth, recrystallisation and softening in the HAZ, and to introduce weld defects that act as stress concentrations and preferential fatigue crack initiation sites. Several fatigue studies of aluminium welds emphasised the role of precipitates, second phase particles and inclusions in initiating fatigue cracks. When simultaneously subjected to a corrosive environment and dynamic loading, the fatigue properties are often adversely affected and even alloys with good corrosion resistance may fail prematurely under conditions promoting fatigue failure. The corrosion-fatigue performance of aluminium welds has not been systematically examined to date.

This investigation aims to find the degree of passivation required to completely inhibit the stress corrosion cracking of carbon steel exposed to CO-CO₂-H₂O environments.

A516 pressure vessel steel was exposed to distilled water with 25 per cent CO and 75 per cent CO₂ at an overall pressure of 800 kPa with the introduction of potassium bichromate as an additional inhibitor. Slow strain-rate tests were performed to evaluate the steel for sensitivity to cracking. Electrochemical characteristics were investigated in parallel in order to determine the extent of passivation required with the addition of the inhibitor.

Slow strain-rate tests showed that between 100 and 1,000 ppm potassium bichromate was required to completely mitigate cracking with a significant reduction in passivation current densities.

The chosen inhibitor is not ideal for practical applications as an inhibitor, but gave an indication of the passivation required.

The results showed that the added inhibitor might even cause increased sensitivity to cracking in this environment, with significant passivation required for resistance to cracking.

The degree of passivation required for complete resistance of carbon steel in 25 per cent CO-75 per cent CO₂-H₂O.

THE best description of this Indicator is published on a large folio four‐page statement written by Mr. John Maclauchlan, Chief Librarian of the Dundee Free Library, and issued on September 22nd, 1879. This sheet is headed, “ Description and Method of using Kennedy's Indicator, invented for the Dundee Free Library in January, 1875, and constantly used therein since July of that year” and contains illustrations of the counter and details of the construction of the Indicator. The following description is abstracted from it:—“This contrivance consists of a series of upright glazed frames so placed as to be easily inspected by the public at the front, or glazed side, and by the library attendants at the back. … Each frame is divided into twenty vertical columns by slips of mahogany, and each of these slips is again sub‐divided into 100 sloping slits by pieces of stiff millboard [now zinc], tightly held in saw cuts made in the sides of the mahogany slips … As the lower edge of each piece of millboard is a little above that of the next one below it, sufficient space is visible of their lower ends in front, and of their upper ends at the back of the Indicator, to receive the catalogue number of each book in the library, printed in bold figures and pasted at the end of the millboard [zinc] strips with strong paste.” Each borrower is provided with a ticket measuring 5⅜ inches by 1 inch, ruled as follows :—