VISCOSITY END ELECTRICAL CONDUCTIVITY OF LIQUID HYPEREUTECTIC ALLOYS Al-Si

Abstract

The kinematic viscosity of AlSi20 liquid alloy was measured by using the crucible rotating oscillation damping method, and the viscosity-temperature relation curve ν(T) in the temperature range of 850∼1200K was obtained. The viscosity changed abnormally with temperature in the heating process, i.e., the viscosity turned from rapid increase to gradual decrease when the temperature increased to 1000∼1100 K, while the viscosity diminishes exponentially with temperature in the subsequent cooling process. The microscopic mechanism of the evolution of viscosity was analyzed from the viewpoint of the micro-inhomogeneity theory of metallic melts, and it was found that the destruction of the β-Si phase was the basic reason of the head-turning change of viscosity. The paper discussed the correlation of the viscosity and atomic density, which is thought that the viscosity corresponds to the atomic density to some extent. The abstract should be written in the past tense, because it refers to work which was already done. Any equations and references are not allowed. It must state the main object, scope, findings, describe the methodology, summarize the results and state the principal conclusions.Keywords: aluminium alloys, liquids, crystallization, microstructure, segregation 1 Introduction Al-Si alloys are amongst the most widely used industrial metallic alloys due to a combination of good cast ability and mechanical performance [1]. Modification of the complex solidification microstructure, aimed at improving the process ability and the mechanical performance, has received continued research attention in these alloys [2][3][4]. Were investigated of influence of melt overheating (up to defined temperature for each alloy) on structure and phase composition of ingots hypereutectic silumi [5]. It is shown that hypereutectic silumin melt keeps the inhomogeneous state in a wide range of overheating above the liquidus temperature ТL, and the most significant structure rearrangement is observed only when heated above the temperature Тk. The large amount of eutectic and primary coarse Si-flakes that form during solidification of the Al-Si hyper-eutectic alloys leading to reduced ductility and wear performance [6][7]. The sessile-drop method and high-temperature small-angle x-ray diffraction technique were used in work [8] to characterize the density of liquid Al-Si alloys with Si content to 22 wt.%. A distinct abnormal volume expansion of the hyper-eutectic melts was identified just above the liquidus (within TL-Tk) during the heating sequence, which is irreversible during the cooling sequence. This phenomenon is explained by the segregation of Si atoms from the supersaturated "quasi-

Modification of AlSi7Mg alloy with Sr and Sb

“…In industrial conditions, modification is carried out with mixtures of one of these two elements (mainly strontium) and salts of various metals. The composition of the mixtures used in industrial conditions to modify silumins remains known only to the alloy manufacturer [19][20][21][22][23][24][25][26][27][28].…”

Effect of Ti and B additions as powder and preliminary alloy with Al-Si alloy on microstructure and mechanical properties of AlSi9Mg alloy intended for parts of agricultural machinery

“…It was found that the addition of modifiers, initially sodium and strontium, to Al-Si casting alloys significantly improves mechanical properties, especially ductility [29][30][31][32]. The influence of strontium on the stability of phase fragmentation and mechanical properties is more noticeable and more durable than that of sodium [32][33][34][35]. The improvement in mechanical properties is generally attributed to changes in the morphology and size of the eutectic particles of the silicon phase.…”

Examining of Solid and Liquid Industrial Copper Blanks with Purpose for Quality Control in Respect of Defects of Technological Origin

“…It is known that the presence of exogenous non-metallic inclusions in the metal affects the melt viscosity [5][6]. It is also known that the heating temperature of the melt affects the structure and properties of the cast metal, including the presence of defects of metallurgical origin in the ingot microstructure: non-metallic inclusions, pores and discontinuity defects [7][8][9][10][11][12]. It was established experimentally that the destruction of the microheterogeneous structure of the melt is usually accompanied by anomalies in the temperature dependences of the melt viscosity.…”

“…The temperature dependences of the melt viscosity corresponding to heating and subsequent cooling were different. In this case, the temperature T *, which corresponds to an irreversible transition of the melt to a more uniform state, was determined from the beginning of the high-temperature coincident segment of the heating and cooling polytherms [7][8][9]. It was proposed to overheat in industrial conditions various melts above the indicated temperatures T *, i.e., to perform temperature treatment of the melt before pouring.…”