The results of a metallographic analysis of a bimetallic bearing assembly for hull parts of marine engineering are presented in the paper. The adhesive properties at the Al-Fe metal boundary are poorly studied at present; the physical processes of strength formation are very heterogeneous and depend on the parameters of the technological process. The samples obtained by stamping a commercial liquid Al-Si-Mg alloy in the presence of powder bush from a pure iron with 15 percent volume porosity have been studied in the paper. Metallographic analysis is performed using a Carl Zeiss Axiovert 200 MAT motorized optical microscope equipped with a Thixomet Pro image analyzer. Samples with different levels of adhesive strength, from unsatisfactory to the highest values, are selected for the research. The strength value correlates well with technological parameters such as stamping pressure and the temperature of preheating of the forming rigging. However, it was found that the mechanisms of Al and Fe compound are different. At low stamping pressures and poor adhesion strength of the compound, the main reason for the lack of contact at the metal boundary is a strong temperature gradient and various rates of shrinkage processes that sever the contact zone. Under conditions of medium stamping pressures, liquid aluminum destroys the ferrite network of the powder bush and penetrates into free pores to a depth of 1-2 mm, forming a high-quality adhesive compound. The bimetal boundary zone has a high density, finely dispersed structure of aluminum without traces of graphite, and the powder bush contains all the signs of secondary crystallization in the form of network structure of a ferrite. Under conditions of high stamping pressures, liquid aluminum interacts with iron, forming metastable intermetallic phases at the metal interface, while aluminum also penetrates into the pores of the ferrite network. The presence of intermetallic compounds increases the adhesive strength of the compound. New physical principles aimed at finalizing the technology for obtaining the bimetallic bearing of marine engineering at the stage of obtaining a workpiece have been identified and disclosed.Keywords: bimetallic bearing, metallographic analysis, marine engineering, adhesive strength. For citation:Kuznetsov, Ruslan V., and Evgeniy O. Olhovik. "Studying the physical processes of forming the adhesive strength of bimetallic bearing for marine engineering." Vestnik Gosudarstvennogo universiteta morskogo i rechnogo flota imeni admirala S. O. Makarova 11.5 (2019): 902-909.В данном исследовании приводятся результаты металлографического анализа биметаллического подшипникового узла для корпусных деталей судового машиностроения. Отмечается, что в настоящее время адгезионные свойства на границе металлов Al-Fe слабо изучены, физические процессы формирования прочности весьма разнородны и зависят от параметров технологического процесса. В работе изучены
The subject of the study is the thermophysical properties of the Al-Fe bimetallic compound obtained by the joint stamping method of liquid metal. The object of the study is the corpus products of marine engineering, which are pumps and hydraulic equipment from commercial Al-Si-Mg alloy with bearing bushings obtained from sintered powder iron. The creation of equipment, laboratory and methodological foundations for the study of thermal processes in the formation of Al-Fe bimetallic compound under stamping pressure is considered in the paper. The method of differential thermal analysis is selected as the main laboratory method for studying thermal processes in the manufacture of a bimetallic compound by liquid metal stamping method, because it provides a relevant study of the temperature parameters of the technological process. The essence of the method is to measure the temperature of the solidifying aluminum alloy, powder bush and technological rigging during the formation of the bimetallic compound. A set of thermocouples, special digital drivers and a microcontroller, which transfers all the information for storage and analysis to a personal computer with a resolution of 1 second, are used to implement the measurements. Several thermal graphs that corresponded to various technological parameters (temperature, pressure) are obtained in the experiments. Comparison with the results of similar studies has showed that a stable adhesive compound is formed due to the mechanical interfusion of metals and filling of the bulk pores in the powder bush with liquid aluminum or due to the formation of a thin diffusion zone, followed by the implementation of a metallurgical compound. The various thermal regimes of the bimetallic compound solidification are investigated at the developed laboratory setup; it has been revealed that the stamping pressure significantly affects the formation of contact between metals, and allows creating a stable adhesive connection.
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