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As a lead-in to the use of 5083 for liquefied natural gas tanks [1], a special series of fracture tests was ran to substantiate that the alloy has high tear resistance in the relatively thick sections in which it would be used in the structure. These tests were similar in nature to the tear tests which have been made for years [2], but covered a much wider range of variables, viz., (1) much thicker material., (2) specimens from the heat-affected zone as well as the parent metal and the welds, (3) welds made automatically, semiautomatically, and in different positions (flat, vertical, horizontal), and (4) welds in extruded shapes as well as plate. The purposes of this paper are to describe the test procedures, present the results, and discuss their meaning as an indication of the toughness of 5083 for engineering structures.

The mechanical properties of aluminum alioys have been well documented at temperatures down to -320°F for many years [1–3] and, within the past few years, a reasonable amount of information has been developed at -423°F with liquid hydrogen as the cooling agent [4–7]. Nevertheless, little has been known of the properties of aluminum alloys at -452°F, the temperature of liquid helium; only one alloy, 5083, has been thoroughly evaluated prior to 1966 [8].

At present, the 2000(Cu), 5000(Mg), 6000(Mg-Si) series provide most of the aluminum alloys used in cryogenic applications. Established alloys in the 7000(Zn) series, including 7075, 7079, and 7178, are more sensitive to notches than many of the alloys of the above types [1,2] and have not been seriously considered. Recently, several new 7000-series alloys have been introduced with appreciably greater notch toughness than other alloys of this type. It is. expected that these new alloys may be of considerable use in cryogenic applications.

There are some applications where aluminum alloy castings, because of the ease with which they can be made into relatively complex shapes, would be very desirable for service at cryogenic temperatures. Parts which would require extensive machining from plate or hand forgings and are too intricate for the effective use of die forgings, would be suited ideally for fabrication by casting.

An impressive amount of literature has been developed to define the tensile properties and notch toughnesses of aluminum alloys at very low cryogenic temperatures [1–3], Data and service experience are consistent in indicating the suitability of many aluminum alloys for cryogenic service, since they retain their relatively high ductility and notch toughness, in addition to having useful strengths at very low temperatures. Although a fair amount of data have been presented on the tensile properties and notch toughness of welds in aluminum alloys [4,5], none have been available for liquid-helium temperature to provide a guide as to which particular combinations of parent and filler alloys might be most desirable for extremely low-temperature service.

Among the readily weldable aluminum alloys showing great promise for cryogenic applications, 2219[1,2] appears to be outstanding. In tests made recently at NASA Lewis Research Laboratories[3], the strengths of both smooth and notched specimens from 2219-T62 sheet (plain, as-welded, and reheat-treated and aged-after-welding) were shown to increase with decrease in temperature to -423°F. The elongations generally remained relatively high. This alloy appears to offer medium-high strength and high toughness similar to that of the high-strength aluminum-magnesium series of alloys plus the advantages of response to postweld thermal treatments.

Because of the economic advantages in utilizing aluminum alloys for applications at very low temperatures, data were published in 1967 and 1968 for a variety of 2XXX and 5XXX aluminum alloys and for welds in those alloys at -452°F [1’2] showing their high strength, ductility, and toughness. This program has now been extended to include 7XXX alloys in several tempers.