G ray cast iron is being widely used in the industrial market due to its low price and excellent properties such as low melting temperature, minimum shrinkage, deformation resistance and corrosion resistance [1,2] . Over the past decade, more than 70% of the world's cast materials are gray cast iron [1] . However, gray cast iron has poor tensile strength, high brittleness and high density compared with new iron alloys. These disadvantages may hinder the use of gray cast iron in many specific applications [2] . However, the tensile strength can be improved through optimum selection of iron compositions, casting method, and sintering phenomenon [3] . Recently, the tensile strength of gray cast iron has been improved significantly by adding small amounts of alloying elements to the iron's matrix to control the microstructure. These alloying elements are Abstract: Experiments were carried out to observe the variation in microstructure and mechanical properties of gray cast iron by adding pearlite promoting alloying elements such as Ti, Sn and W. Results show that adding Sn, Ti, and W with different concentrations improve the microstructure, Brinell hardness and tensile strength of gray cast iron. With the increase of alloying element concentration, the average graphite length and graphite content increase linearly. At the same time, average cell size and the maximum graphite length also decrease linearly. Brinell hardness and tensile strength of gray cast iron also increase with an increase in alloying elements contents, and attain the maximum when Ti = 0.561%, Sn = 0.561% and W = 0.945%. However, at higher concentrations of Ti = 0.810%, Sn = 0.631% and W = 1.351%, the tensile strength decreases from 333 MPa to 297 MPa and the Brinell hardness decreases from 248 HB to 225 HB. The decrease in tensile strength and Brinell hardness at the higher concentration level is attributed to the formation of coarse and thick graphite flakes.

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In this paper, the physical simulation of filling process of vertical centrifugal casting (VCC) of complex titanium alloy casting was studied. Combined with the mature PTV particle tracking technology, the high-speed photography pictures of the filling process of VCC at different rotational speeds were obtained. The trajectory and velocity information of tracer particles in the rotating flow field were obtained by the corresponding analysis software. Then, through the analysis and modeling of quantitative experimental data, the flow behavior characteristics and movement law of titanium alloy melt in the mold cavity under different mold speeds were studied. The results show that: 1. When the mold is still, the front edge of the filling fluid forms a curved surface with the curvature center pointing to the outside of the mold; when the mold rotates, the front edge of the liquid flow forms a curved surface with the curvature center pointing to the inside of the mold; 2. With the increase of the mold rotation speed, the speed of the fluid filling the mold increases significantly; when the rotational speed is greater than 120 rpm, the fluid still has a certain driving force in the mold center far away from the gate It is good for filling the inner corner of mold with fluid; 3. When the rotational speed of centrifugal casting of titanium alloy reaches 45 rpm or above, typical turbulent vortices appear in the wake; with the increase of rotating speed to 180 rpm, the average curvature radius of turbulent vortices first increases and then decreases, and reaches the minimum value of 0.67 cm at 120 rpm.