| The high strength and good comprehensive mechanical properties of the ZL205A alloy castings have been widely used in aviation, aerospace and other fields, but it is easy to produce shrinkage cavity, shrinkage porosity and other casting defects. The Vacuum Counter-pressure Casting (VCPC) is an advanced anti-gravity casting method, and has certain advantages in the casting of complex thin-walled aluminum castings. In this paper, based on the traditional VCPC process, solidification process using grade-controlled on ZL205A alloy microstructure were studied, the results of the study provide theory and technique supports for obtaining dense high quality ZL205A casting, have great theoretical and practical significance.This paper adopted VCPC-I equipment, under the condition of grade-controlled solidification, studied the influence of the level pressurized solidification pressure, the grade-controlled solidification pressure, sample thickness on microstructure of ZL205A alloy castings. The results show that pressurized solidification pressure have a greater influence on microstructure, with the increase of level pressurized solidification pressure, the microstructure refined and the grain size decreased; however, with the increase of sample thickness, the microstructure was coarsened and the grain size increased. Samples prepared by grade-controlled solidification, the grain size is less than that of samples prepared by level pressurized solidification, with the increase of grade-controlled solidification pressure, the microstructure refined and grain size decreased; with the increase of sample thickness, the microstructure was coarsened and the grain size increased, however, when grade-controlled solidification pressure is equal or less than300KPa, it has little effect on grain size, sample thickness has great effect on the grain size; when grade-controlled solidification pressure is greater than300KPa, it has great effect on grain size, sample thickness has little effect on the grain size.The relationship of grain size and grade-controlled solidification pressure and the sample thickness during the grade-controlled solidification of VCPC were obtained and shown as below:Studied the effect of the grade-controlled solidification on grain boundary segregation of VCPC ZL205A casting, with the increase of grade-controlledsolidification pressure, segregation organization of grain boundary have evolved frommassive bone shape into fine mesh and fragmented, segregation organization are all θ(Al2Cu) phase, a small amount of dark gray T(Al12CuMn2) phase distribute on the grainboundaries. After T6heat treatment, the grain boundary segregation of the ZL205Aalloy diminished to some extent. The results show that grade-controlled solidificationpressure of VCPC has a little influence on grain boundary segregation. The results ofthe study provide the theoretical basis for producting ZL205A alloy castings bygrade-controlled solidification of VCPC, and have important significance for the use ofVCPC. |
