Formation of sylicides of aluminium in the Al-Si-Ti system

Abstract

Currently used discrete fillers of cast aluminum matrix composite antifriction materials in most cases are characterized by high hardness, leading to increased wear of steel pairs of friction, which makes the search for new fillers urgent. Due to the formation of titanium aluminosilicates in the Al-Ti-Si system and the insignificant solubility of silicon and titanium in aluminum, it was suggested that it is possible to obtain composite materials based on them by the in-situ method or by synthesizing reinforcing materials in a liquid metal matrix. The introduction of titanium in the amount of 10 wt. % into the melts of Al-10÷20 wt. % Si at 700, 800 and 900 °C and subsequent isothermal holding the composite materials are synthesized. By melting in the range of 1000-1100 °C the Al-10÷25 wt. % Si-5÷15 wt. % Ti materials are obtained The phase composition of these materials and the content of elements in the primary phases formed in the aluminum matrix, the hardness of materials obtained by melting is determined. Studies of the formation of phases in the Al-Si-Ti system showed that under the conditions of their synthesis in the liquid phase as a result of reaction-diffusion, a large spectrum of aluminosilicates is formed, which are characterized by a dispersed structure. Under such conditions, since the processes are far from equilibrium, the formation of phases that cannot form during crystallization from the melt under conditions of its cooling is possible. This makes it possible, by varying the synthesis temperature and composition of the charge materials, in wide intervals, to change the properties of the resulting aluminum-matrix composite materials. Similar composite alloys that form during crystallization from the melt are characterized by a more coarse-crystalline structure and a substantially smaller spectrum of silicides, which obviously impairs their properties. The tests of the composite material of composition 85 % Al-15 % Si – 10 % Ti for friction-wear showed that it is characterized by high tribological characteristics. A significant advantage of the materials of the Al-Si-Ti system is the absence of solid phases capable of damaging the surface of the counter body made of steel. This makes promising further studies of the tribotechnical characteristics of the composites of this system.