Precipation of TiAl₃ in remelting Al-5Ti-1B and the grain refinement of 7050 alloy

This paper studies the precipitation regularity of TiAl₃ compound in different temperature, holding time and cooling rate. Besides, this paper studies the influence of Al-5Ti-1B on the mechanical properties of the 7050 alloy such as the aluminum alloy grain size, microstructure and strength through changing holding time and amount of Al-5Ti-1B. Through water cooling, the solute Ti forms new fine TiAl₃ compounds firstly. While through natural cooling, the solute Ti is easy to grow up around the agglomerate TiAl₃ compounds. The variation of the undissolved TiAl₃ compound as follows: the size of the block-like TiAl₃ does not change at 700 °C for 10 min; while the size has stabilized at 750 °C for 5 min. The dissolution of the rod-like TiAl₃ is not obvious when holding for 20 min, but the rod-like TiAl₃ fuses easily. After adding the Al-5Ti-1B into the 7050 alloy, the grain shape of α-Al changes from dendritic crystal to equiaxed crystal, and the refining effect is obvious; While the adding amount increases, the size of α-Al become larger, but it has a tendency towards to dendritic crystal. The mechanical properties of 7050 alloy without Al-5Ti-1B is in the worst condition. Transcrystalline rupture may occur in grain of 7050 alloy in tensile test due to it is coarse grain. After adding the refiner, the mechanical properties are optimal when keeping the temperature 750 °C for 5 min. Dimple could be found in the tensile fracture, and the dimples mainly are equiaxial. (paper)