立式离心铸造钛合金薄壁复杂铸件宏观偏析研究

Study of the Macrosegregation of Thin-walled and Complicated Titanium Alloy Castings Produced via the Vertical Centrifugal Casting Process

立式离心铸造过程中,由于离心压力在铸件不同半径处有梯度性,会形成严重的宏观偏析。以立式离心铸造TC4钛合金薄壁复杂铸件为研究对象,阐明铸型转速、离心半径及壁厚对铸件宏观偏析的影响规律。结果表明,提高铸型转速会加重钛合金铸件的宏观偏析。当离心半径较小时,钛合金铸件中钒和铝的含量较高;当离心半径较大时,钒和铝的含量较低,形成负偏析。钛元素含量的分布正好与此相反,形成正偏析。离心半径为71 mm时,铸件薄壁部位钛、铝、钒含量为88.1%、8.1%和4.1%;离心半径增加到143 mm时,钛、铝、钒含量为89.9%、7.7%和3.6%(质量分数)。在铸件厚壁部位,其冷却速度比薄壁部位大,合金元素的升高或降低趋势更明显,偏析更严重。整体而言,该薄壁复杂钛合金铸件的偏析不严重。

Macrosegregation usually occurs during the vertical centrifugal casting process because of the pressure gradient at different positions during casting.TC4 alloy castings with complicated shapes were produced via a vertical centrifugal casting process,and the effects of the mold rotational speed,centrifugal radius and casting wall thickness on the macrosegregation of the castings were investigated.The results show that macrosegregation in castings produced by the vertical centrifugal casting is greatly enhanced by increasing the rotational speed of the mold.The contents of V and Al in the TC4 castings with smaller centrifugal radii are greater,whereas they are lower in those with larger centrifugal radii,further promoting positive segregation.The distribution of Ti is different from that of V and Al,and it results in negative segregation.The contents of Ti,Al and V at a radius of 71 mm are 88.1 wt.%,8.1 wt.%and 4.1 wt.%,respectively,and those at a radius of 143 mm are 89.9 wt.%,7.7 wt.%and 3.6 wt.%,respectively.Element macrosegregation is much more obvious in castings with greater wall thicknesses than in those with thin wall thicknesses because of the lower cooling rates.Overall,the segregation of TC4 alloy castings with complicated shapes is not substantial.