Effect of Ti, Sc and Zr Additions on as-Cast Microstructures of 7005 Aluminum Alloy

7005 aluminum alloys containing Ti, Sc and Zr were prepared. The microstructures of 7005 aluminum alloys were studied using optical microscope, scanning electron microscope (SEM) and EDS. The results show that the grains of 7005 alloy refined by Grain-refining Aluminum Ingots containing 0.112 wt%Ti produced by electrolysis (GRAI) are much smaller than that by Al-Ti master alloy, but dendritic structures appear in both of them. The grain average diameters in both of them are about 170 mu m and 330 mu m, respectively. Simultaneous adding minor Sc, Zr and/or Ti (from GRAI) to 7005 aluminum alloy can greatly refine as-cast grains of alloys. The grain average diameters are about 35 mu m and 50 mu m, respectively, and dendritic structures disappear in both of them. The simultaneous additions of Ti (from GRAI), Sc and Zr lead to further grain refinement, because a number of Al3Sc, Al-3(ScxZr1-x) and Al-3(ScxTi1-x) particles form in the alloy. These particles play a role of heterogeneous nucleation. After homogenization at 470 degrees C for 24 h for 7005 alloy, the eutectic phases on the grain boundaries are spheroidized, and a large number of small spherical particles containing Al, Zn and Mg elements appeare around grain boundaries, the solute segregation around grain boundaries disappeares.