Effect Of The Reactive Additions On The SiCp/Al Composites Fabricated By The Pressureless Infiltration Technique

The Pressureless Infiltration Technique means that the spontaneous infiltration of the refined molten Al or Al-Si alloy into the power bed , contains the filler reinforcement particle and K2TiP4, occurred at 900 to fabricate SiCp/Al or SiCp/Al-Si composites, without the aid of any externally applied pressure or vacuum, only by its gravity. The technique require simple process and equipment, so the cost is low, It's a promising method for fabricating MMCs. The MMCs made by the method offer high strength and modulus as well as good high-temperature properties, when compared to corresponding monolithic alloys and they are promising materials for automotive and aerospace industry applications.However, the following two difficulties still exist: 1. Wetting between reinforcement SiCp and the molten metal is often poor when it is blow 1000'C; 2.During the processing, many phases of the interfacial reaction products have negative influence on the properties of the produced composites. The problems can be addressed, in part, through a strongly reactive alloying addition ,such as Mg, Li and so on, and through reinforcement coating .In this paper SiCp/Al composites and SiCp/Al-Si composites fabricated by the pressureless infiltration method . In order to found out the influence the different quantity of the reactive alloying addition Mg Si Ce on the wetting between SiCp and molten metal as well as the properties of MMCs , the behaviors of molten metal ,the mechanical properties, micro-structure and the interfacial reactions was investigated respectively .The results indicate that: the addition of Mg decreases the surface tension of molten Al and Al-Si alloy, reduce the solid/liquid interfacial energy and induce chemical reaction at the interface .so it improves wetting of Al and Al-Si metal and SiCp ceramic system .The most significant influence occurred at 1.0% Mg on both SiCp/Al composites and SiCp/Al-Si composites. The addition of Mg reactswith Al and SiO2 then form MgAl2O4 at the interface in the SiCp/Al composites; It reacts with SiO2 and produce MgO at the interface in SiCp/Al-Si composites, the good metal-ceramic bond is achieved. Mg can prevent the fragile AUC3 phase from producing, then the properties of the MMCs are improved. The addition of Ce can also improve the wetting between Al-Si-SiCp ceramic system. While it influent on the Al-SiCp ceramic system more effectively. Because the reactive alloying addition Ce react with Si in molten Al-Si and form stable compound CesSis .Therefore , when Ce is 0.3% and 0.9% can improve the wetting most significantly of Al-SiCp system and Al-Si-SiCp system respectively. Comparing the micro-structure and properties of SiCp/Al composites and SiCp/Al-Si composites ,we know that the addition of 11-13% Si can counteract the fragile Al4Cs phase obviously. At the same time Si causes significant changes to the viscosity of molten Al and Al-Si alloy and enhances wetting between SiCp ceramic and molten metal.