Effect Of Antimony Addition On The Microstructure And High Temperature Properties Of AZ31 Alloy

Magnesium alloys have attracted increasing attention for potential application in the industries due to their merits of low density and high specific strength and so on. However, the range of the applications for the alloys is limited by its lower strength and poor creep resistance at high temperature. In order to improve the properties of the alloy, the effect of antimony addition on the microstructure and performance of AZ31 alloy, and deformation mechanism during creep have been studied by means of measurement of creep curves, XRD analysis and microstructure observation of TEM.The results show that small antimony additions to AZ31 alloy improve effectively high temperature properties, for example, the ultimate tensile strength of AZ31-0.84%Sb alloy under room temperature and 200℃ is 297 MPa and 189MPa respectively. In the range of the applied stresses and temperatures, the internal frictional stress of dislocation movement for the alloy during creep exhibits an obvious sensitivity to temperature, the value of the internal stress rapidly decreases over 175 ℃. During creep under the condition of the applied stress of 50 MPa at 150℃ and 175℃, the alloy displays a higher creep resistance and lower strain rate, so that the enduring lifetimes of the one are more than 1200 hours. And the creep regularity of the alloy is in accordance with the rate equation given as follows:During steady state creep, the activation energy (Q) of AZ31-0.84%Sb alloy has been calculated to be 145±10 kJ/mol, and there are different stress exponents under the applieddifferent stresses.The fact that high volume fraction of the second phases precipitated in the matrix ofAZ31-0.84%Sb alloy is the main reason for displaying the better high temperature properties. Especially, a large number of Mg₃Sb₂ phases with high melting point areprecipitated homogeneously in the matrix of the alloy, which effectively hinders the movement of dislocations and slipping of the grain boundary during the elevated temperature deformation. The dispersion extent of the second phase distributed in the alloy may be improved by heat treatment, which enhances the ultimate tensile strength and creep resistance, in further, and decreases the temperature sensitivity of the internal frictional stress. By means of microstructure observation and contrast analysis, it is shown that the main deformation mechanism during creep of both AZ31 and AZ31-0.84%Sb alloy is significant amount of the straight dislocation activated in the matrix. The slip of < a > and < a + c > dislocations can be activated, respectively, on basal planes, prism and pyramidal planes. The slip of < a > dislocations activated on the prism plane may cross-slip to pyramidal plane by means of dislocations reaction. Twinning deformation in the alloy may occur in the role of the compatibility stress. Twin boundaries in the form of multiple parallel groups can hinder dislocations movement, but the little change of the crystal orientation in the twinning region may activate again the slip of dislocation within twinning. Therefore, twinning as an additional deformation mechanism may improve the ductility of some alloy with hep structure.