Effects Of Cr And Yb Additions On Microstructures And Mechanical Properties Of2519A Aluminum Alloy

2519A aluminum alloy is used for amor plate,there is vital relations between its mechanical properties and impact property. For further improving the impact property of2519A alloy, the effects of composite additions of Cr and Yb on microstructures and mechanical properties at room and elevated temperatures of2519A aluminum alloy were investigated in this thesis by optical microscopy (OM), Vickers hardness-testing device, scanning electron microscopy (SEM), transmission X-ray diffractometer (XRD), electron microscopy (TEM), and tensile tests. The main conclusions are listed in the following:(1) The effects of Cr and Yb on as-cast grains sizes of2519A aluminum alloy was investigated. The as-cast grains of2519A alloy were refined with a certain separate single additions of Cr or Yb and composite additions of Cr and Yb. Compared with0.11Yb,0.17Cr addition has a higher efficiency, the average size of the as-cast grains decreased from101μm to62μm. Composite additions of0.18Cr and0.1Yb have the same efficiency with0.17Cr additions, and the average size of as-cast grains of this alloy is58um.(2) The influence of the composite additions of Cr and Yb on the aging precipitation sequence of2519A alloy did not change. However element Yb in2519A alloy plate can suppress the formation of G.P. zone and accelerate aging process. Cr did not have this effect.(3) The distribution and existence form of Yb in different alloys were investigated. In the alloy with0.11Yb, the undissolved Yb atoms existed in the form of AlCuYbphase. But in the alloy with0.1Yb and0.18Cr, the undissolved Yb atoms formed some new phases, which contained elements of Cr and Mn, the same time, the amount of rare earth-rich phase is less than the alloy with0.11Yb. The rare earth-rich phases were stable along grain boundaries at300℃, which were able enhance the grain boundaries strength of the alloy. The ressult of XRD showed that, the alloy with Cr and Yb will precipitate some dispersoids in the process of heat treating. Some of this dispersoids contain element Cr、Mn and some of this dispersoids are Al20Cr2Yb phase. This dispersoids have strengthency function,they can block the motion of the dislocations, therefor enhance the grain boundaries strength of alloy at elevated temperatures, and improve mechanical properties both of room and elevated temperatures.(4) The effect of composite additions of Cr and Yb on mechanical properties at room and elevated temperatures of2519A aluminum was investigated. Both of separate addition of Cr or Yb can improve the mechanical properties of the alloys, but composite addition of Cr and Yb has the best result. The ultimate tensile strength at room and elevated temperatures reaches508.9MPa and167.7MPa. The improvement of strengthe of the alloys at room temperature are related to the high density of0’precipitates. Furthermore, the enhancement of thermal stability of the alloys at elevated temperature can attribut to both the denser and finer0’phase, to the grain boundaries due to the rare earth-rich phases and dispersoids.