Effect of interfacial reaction on the Young's modulus of aluminium borate whisker reinforced aluminium composite

Abstract

The interface plays a very important role in the properties of composites. One of the effects of the interface on the properties of the composite is that it may affect the load transfer from the matrix to the reinforcement. As it is well known that the Young's modulus of composites is influenced mainly by the load transfer [1, 2], the interfacial reaction has a great effect on the bonding and strength of the interface [3], which can affect the Young's modulus of the composite. Recently, a low cost aluminium matrix composite reinforced by aluminium borate whisker (AIIsB4 O33W » denoted by ABOw) has been studied by many researchers [4 8]. Although the interfacial reaction, mechanical properties and ageing behaviours of the composite have been investigated extensively, there have been few studies on the effect of the interfacial reaction on the Young's modulus of ABOw/A1 composite. This letter aims to report this effect. The ABOw/AC8A-A1 composite used was fabricated by the squeeze casting method. The volume fraction of the whisker was 25%. The composition of the matrix alloy was Si: 12.0wt%, Mg: 1.0wt%, Cu: 0.8 wt%, NJ: 1.0 wt%, AI: 85.2 wt%. To obtain different degrees of the interfacial reaction, the composites were fabricated at various temperatures: 660°C, 720°C, 760°C, 800°C and 840°C. The specimens for tensile testing were solutionized at 500 °C for 5 h then quenched into water maintained at 80 °C, to prevent the effect of precipitation on the properties of the composite. The microstructure and the interfacial reaction were studied by transmission electron microscopy (TEM). The specimens for TEM observation were thinned by the ion milling method. The Young's modulus of the composite was measured by the slope of the tensile stress-strain curves. The dependence of Young's modulus of the composites on the casting temperature is shown in Fig. 1. It can be seen that when the casting temperature is lower than 800°C, the Young's modulus of the composite increases with the casting temperature. When the casting temperature is higher that 800 °C, however, the Young's modulus of the composite decreases with increasing casting temperature. That is to say, there exists an optimal casting temperature for the Yourig's modulus of the ABOw/AC8A composite. The microstructure of the ABOw/AC8A composite was studied using TEM. As shown in Fig. 2, an