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Cold treatment is used for decreasing the amount of retained austenite in hardened steel. Cooling to low temperatures can also be effective for alloys that do not undergo a martensite transformation, for example. alloys based on aluminum and nickel. The article concerns special features of treatment of alloys of grades AMtsM, ADIM, and NP-21~ in liquid nitrogen.Cold treatment is widely used in heat treatment of metals [I, 2]. However, until recently, the effect of the "rest" time in cold treatment on the properties of alloys has not been investigated properly.We developed a method for treating metal in liquid nitrogen with subsequent heating and "rest" [3]. The technology of this treatment consists in cooling the metal to the temperature of liquid nitrogen (-196°C), heating to room temperature, a hold ("rest"), and deformation (shaping of parts). We established ( Fig. i) that in the process of this hold the plasticity and strength of a ribbon of aluminum ADIM (Table l) with a thickness of 0.3 mm are increased. The largest increase in the plasticity is attained after a "rest" for 24 h. Directly after heating or in a few hours, the plasticity and the strength can be lower than in the initial (annealed) state.A similar effect is observed for ribbons of aluminum alloy AMtsM treated by the same method (Tables I, 2).It should be noted that in some heats the strength and the plasticity do not increase (Table2). In some cases the strength can remain the same and the plasticity can grow. It has been shown in [4] that after treatment by liquid nitrogen and a "rest" the depth of extrusion and the stamping capacity of sheets of AMtsM with a thickness of 0.6 mm are increased.The mechanism of the effect of liquid nitrogen seems to consist in self-curing of microinhomogeneities (micropores, microcracks, vacancies), for example, by rehabilitating dislocations [5]. The subsequent "rest" promotes relaxation of stresses and reverse development of some cracks due to the elastic aftereffect of the metal. The change in the mechanical properties in this case is determined by residual phenomena, namely, relaxation of stresses and closing of microinhomogeneities. The absence of the effect of increased plasticity in some batches of metal (Table 2) can be explained by the un- Plant, Lesnoi, Sverdlovsk Region, Russia. favorable state of the microinhomogeneities after rolling and annealing.It is more efficient to use treatment in liquid nitrogen and "rest" for cold-hardened metal, because it contains more microinhomogeneities than annealed metal. Specimens of annealed ribbon 0.3 mm thick of alloy ADlM were cold-hardened with extension at a stress constituting 10, 30, 50, and

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