Effect of cooling rate during crystallization on the structure of B95 and D16 alloys

It is known that the alloys of the Al-Zn-Mg-Cu and Al-Mg-Cu systems have a very wide crystallization interval (over 100°C) and therefore the technology of roll pouring-rolling of sheet blanks from such alloys has not yet been developed. In this regard, the development of scientific and technological foundations of roll casting for such a range of aluminum alloys is an important scientific and practical task. The purpose of this work is to determine the possibility of aluminum alloys B95 and D16 (crystallization intervals are 160°C and 132°C, respectively) for casting-rolling based on the analysis of the effect of cooling intensity on their structure and mechanical properties. The research was carried out on full-scale samples of B95 and D16 alloys by comparing the obtained experimental values. Determination of the temperature parameters of phase transformations in the studied alloys was carried out using the Derivatograph Q-1500-D device. As a result of the tests, the curves of the differential thermal analysis and the fraction of the liquid phase depending on the temperature were obtained. Based on the results of the research, the suitability of B95 and D16 aluminum alloys for casting and rolling has been substantiated. It was found that the size of α-phase grains for B95 and D16 alloys as the cooling rate increases decreases to 120...200 μm (for cooling rates of 2.5...8.8°С/s), and to 40...70 μm (for cooling rates cooling ~1000°С/s). It has been proven that the hardness of B95 and D16 aluminum alloys mainly depends on the α-phase, therefore, when developing roll casting modes, it is advisable to take into account the hardening features of this structural component (α-phase). At the same time, it should be noted that at the intensity of heat removal, which is typical for roll crystallizers, the obtained sheet blanks from the studied alloys will have dispersed crystal structures with a uniform distribution of phase components along their cross sections. A natural consequence of such primary crystalline structures of cast blanks will be a guaranteed high level of strength characteristics of sheet metal rolled from them. Keywords: cooling rate, alloy, crystallization, structure, phase composition, metal rolling