The effect of low-strain pre-stretching at 77K on quenching residual stress and tensile properties of 6061 aluminum alloys

The quenching residual stress in aluminum alloy thick sheets can be generated easily by the gradient temperature difference between the surface and interior caused by uneven cooling. It can cause distortion of components during the process of machining and service. Furthermore, residual stress concentration can reduce the mechanical properties, fatigue performance, corrosion resistance and so on. The pre-stretching is an effective method to release residual stress. The higher degree of plastic deformation during pre-stretching the greater the release of residual stress. However, great plastic deformation can be detrimental to the properties, due to the relative low plasticity of aluminum alloy. Considering the simultaneous increase in both strength and plasticity of aluminum alloy at cryogenic temperature, the effect of low-strain pre-stretching at 77K on quenching residual stress and tensile properties of 6061 aluminum alloy are investigated in the present. The electronic universal testing machine (UTM5305X) is used for the tensile testing. The testing machine is equipped with a self-developed environmental tank. Residual stress of the sample after different treatments is tested by blind hole-drilling method. The stress distribution from surface to 1 mm depth of the sample can be obtained by using Hole-Drilling Residual Stress Calculation Program (version 3.30) software. The effects between room temperature and cryogenic temperature pre-stretching is compared. It is revealed that low-strain pre-stretching at 77K can release the quenching residual stress more obvious, as well as improve the strength and plasticity of 6061 aluminum alloy.

Key words: Pre-stretching, Cryogenic temperature, Tensile property, Residual stress, 6061 aluminum alloys