Effect of cryogenic temperatures on mechanical properties of experimental alloys of the AMg6N type

Abstract

1. The mechanical properties of AMg6N alloys and welded joints vary mainly with the testing temperature. When the temperature is lowered to −269° the strength characteristics increase, the toughness decreases, and the ductility remains at practically the same level as at standard temperature, reaching a maximum value at the temperature of liquid nitrogen. The ultimate tensile strength and the yield strength of the base metal increase 40% in this case, and those of welded joints by 20%. The toughness decreases by a factor of three to four. 2. For all the alloys investigated the stress intensity factor decreases (10–15%) in tests of samples with a sharp notch in the temperature range from +20 to −269°. 3. The elevated notch sensitivity of the base metal and welded joints and the sharp reduction of the toughness of AMg6N alloys cooled to the temperature of liquid helium can be taken as an indication that the metal is transformed to the quasibrittle condition. 4. For alloys of high purity the ultimate tensile strength of the base metal and of welded joints is 5–7 kg/mm2 higher (and the ductility and toughness are 1.5–2 times higher) than that of standard alloy AMg6N.