Study On Compressive Creep Behavior Of The Heat-resistant Magnesium Alloys

Firstly, the effects of Ca, Sr and RE on compressive creep behavior of AE41 were studied at 150℃and 100MPa in this paper. The microstructures of the alloys before and after compressive tests were analyzed by OM, XRD, SEM and EDS. And then, the compressive creep behavior of AEX4112 and AECJ411002 alloys were investigated at different temperatures and compressive stresses. The corresponding stress exponents, creep activation energies and material structural constants were obtained, and the mechanisms of compressive creep were discussed.The results indicate:(1) The creep resistances improve with the addition of Ca, Sr alloys at 150℃and 100MPa. When NdPr rare-earth mixture is replaced by LPC rare-earth mixture, the creep resistance of AEX4108 alloy decreases, but it is still better than that of AE41 alloy.(2) The microstructure of AE41 is composed ofα-Mg matrix and Al₁₁Nd₃ phase. The acicular Al₁₁Nd₃ phase is gradually replaced by Al₂Ca, Al₄Sr, and small amount of Al₂Nd after Ca and Sr addition into AE41. The Al₁₁Nd₃ phase decreases and the Al₂Ca phase increases with the increasing of Ca. The Al₁₁Nd₃ phase distributes along or across grain boundary. The Al₂Ca and Al₄Sr phases locate in grain boundary and the Al₂Nd phase mainly exists within the grain. (3) The poor creep resistance of AE41 alloy is because the Al₁₁Nd₃ phase is prone to decompose into Al₂Nd phase and Mg₁₇Al(12) phase at high temperature. The reason that the creep resistances enhance after Ca and Sr addition is that the Al₂Ca and Al₄Sr phases distributing at grain boundaries have high thermal stability, which can restrain the slippage of the matrix and the grain boundary. At the same time, the Al₁₁Nd₃ phase decreases with the consumption of Al.(4) Under the temperature conditions(125℃, 150℃, 175℃) and the compressive stress conditions (88MPa, 100MPa, 112MPa), the compressive creep deformations and the compressive creep rates of AEX4112 alloy and AECJ411002 alloy increase with the increasing of temperature and compressive stress. The steady creep rate obeys an empirical equation (?)=Aσⁿexp(-Q_a/RT).(5) For AEX4112, the stress exponent (n) are similar at different temperatures and the apparent activation energies (Q_a) are not greatly different under different stresses, as well as AECJ411002. The averages are 6.24 and 37.51kJ/mol for AEX4112 alloy, respectively, 6.19 and 39.05kJ/mol for AECJ411002 alloy. They are far less than the self diffusion activation energy 135kJ/mol for Mg, the diffusion activation energy 143kJ/mol of Al within Mg and the diffusion activation energy 80kJ/mol for grain boundary. While they are similar to the activation energy 30kJ/mol of non-continuous precipitated Mg₁₇Al(12) phase. So, the creep mechanism is controlled by the dislocate climb.