PHYSICO-CHEMICAL METHODS OF INCREASING THE CRACK RESISTANCE OF ALLOY AM4.5Cd (VAL10). NOTICE 1: EXPERIENCE OF USING AN RING SAMPLE

Abstract

On the example of the AM4.5Kd (VAL10) alloy treated in the liquid state with hydrogen, the efficiency of using the well-known ring test for the study of physicochemical methods of influencing the crack resistance of wide-range aluminum alloys, which are prone to the formation of hot cracks during solidification, was studied. To achieve this goal, an annular mold mold was made according to the recommended dimensions, experiments were carried out on the effect of hydrogen treatment of the melt on the crack resistance of castings. Saturation with hydrogen was carried out by blowing the melt with water vapor, the degree of gas saturation was estimated from the porosity of the castings, calculated from the change in their density compared to the control sample obtained in a mold with sufficient power. Despite the measures taken to increase the sensitivity of the annular sample and obtain stable results, which consisted in adjusting the dimensions of the mold, in particular, the size of the central rod, during compression of which the hardening melt creates tensile stresses leading to the formation of a hot crack, as well as optimizing the thermal regime for obtaining a casting by increasing the initial mold temperature from 22 0С to 217-249 0С, the sensitivity of this sample under the experimental conditions remained too low. In 60 % of cases, gas saturation of the melt contributed to a reduction in the crack propagation process when using a mold at room temperature and up to 100 % when the mold was heated to a temperature of 228 0C to 260 0C. However, in both the first and second cases, 28 % of similar data were obtained on castings from the initial melt not saturated with hydrogen. This casts doubt on the reliability of the positive effect of hydrogen treatment and became the basis for the conclusion that it is inappropriate to use this type of sample in studies of physical and chemical effects on the melt in order to increase the crack resistance of the AM4.5Kd (VAL10) alloy due to a possible error in assessing the effectiveness of their impact, and also to decide on the need to develop a new sample, devoid of the identified shortcomings.