Effect of Cryogenic Treatment on Mechanical Properties and Microstructures of 3102 Al-Alloy

The mechanical properties and microstructures of different state cryogenic treatment 3102 Al-foil, such as H19，H26 or O state, were studied by tensile testing, optical metalloscopy (OM) and transmission electron microscope(TEM). The results showed that, after deep cryogenic treatment, the strength of H19 state increased and the elongation to failure decreased. In the same time, the yield strength increased and breaking strength decreases and the elongation decreased dramatically for O state, but, for H26 state, the strength and elongation increased dramatically, which correspond to the properties of this state at low temperatures. OM and TEM observation showed cryogenic treatment caused by the fibrous grains broken down and many grains with the size of 0.1~3μm These fine equiaxial grains can improve the strength and elongation of the Al-foil. On the contrary, the atomic shrinkage force slips high density dislocations into interface of the grains and forms terraces and fissure in it. That leads to the elongation decrease and the interface been broaden at very low temperature. The grain size of O state with cryogenic treatment is larger than without cryogenic treatment. As a result, the synthetic mechanical properties of H26 state improved by the way of cryogenic treatment, but the H19 state and O state should avoid use and put at low temperatures.