The dissertation is devoted to the development, improvement, and implementation of advanced technological techniques and equipment for quality management of low-pressure casting of aluminum alloys based on the use of external technological influences.
To create scientific and technological bases for the use of external technological influences in the casting of aluminum alloys to improve the quality of castings and improve the technical and economic indicators of the casting process, regularities, and mechanisms of influence of the main technological factors on the mechanical properties of castings from Ak7ch alloy were established. At the same time, it was found that overpressure from 200 to 600 KPa slightly increases the hardness index, while from 600 to 900 KPa there is a noticeable increase of 30%. The ultimate strength of samples obtained with a crystallization pressure of 600-900 KPa increases by 23%.
Regularities of the influence of several metal wires when pouring into a multi-seat mold on the formation of shrinkage looseness, shrinkage shells and, accordingly, tightness are established. The dependence of the location of shrinkage defects on various methods of metal supply is found. At the same time, it is determined that when metal is laterally fed into the casting, it cools more significantly in the extended casting system, which leads to a decrease in the power efficiency of the casting during hardening. Also, the use of double mold for pouring reduced mold overheating due to a more uniform distribution of heat transfer from the liquid metal to the mold.
Regularities of the effect of zonal cooling on the solidification rate of castings are established. It is shown that when the casting thickness is 0.02 m with the use of zonal cooling with both copper inserts and zonal cooling with water, a dense metal structure is obtained with a maximum local thickening radius of 0.02 m, the hardness when cooling the copper insert is 1117 MPa, and when using water cooling 1019 MPa, that is, when using cooling, the local thickening has a greater solidification rate than the casting cross-section without thickening, which ensures directional solidification. With a casting thickness of 0.015 m and a local thickening radius of 0.02 m, only cooling with a copper insert gives the structure hardness in local thickening greater than the average casting hardness. With water cooling, the hardness in local thickening is lower than the average, but in both cases, it is higher than the permissible one according to TC (according to TC according to the work for Ak7ch HB = 686 MPa). In castings with a wall thickness of 0.01 m, with local thickening radii of 0.02; 0.015 m; the hardness in thickened ones, even with the use of water cooling and cooling with copper inserts, is lower than the average casting hardness. At the same time, it was found that the rate of temperature drop in the crystallization range Tlik = 620 OC and Tsol = 577 OC for cooling with copper inserts is 43 OC/s, with water cooling 22 OC/s, without cooling – 16 OC/s.
Regularities of the influence of pressure during crystallization on the structure formation of the casting along its height are established. Grain grinding is observed from the lower part of the casting to the upper part, which ensures the principle of directional solidification. It is investigated that the pressure value during crystallization affects the solidification kinetics. The obtained experimental data indicate an intensive reduction in the start time of dendritic crystallization, the total curing time. Kinetic curves of the passage of the solidification front along the casting height at different values of P were obtained from experimental curves.
Regression-correlation analysis and mathematical statistics methods were used to analyze the experimental data. Standard methods have been adapted to evaluate the tightness and mechanical properties of aluminum castings obtained from aluminum alloys under low pressure using overpressure during crystallization. An experimental stand has been created to test the technological process of casting aluminum alloys under low pressure.
The results of the study complement the theory of low-pressure casting.
