Research On In-situ Preparation Of Al₂O₃Particles Reinforced Al-Si Matrix Composite With Foundry Dust And Waste Cans

Foundry dust is a kind of industrial solid wastes coming from the production processes in the caption foundry. Waste cans are also the solid wastes from our daily life. In this paper, these two solid wastes are used as raw materials to prepare Al2O3/Al-Si matrix composite through powder metallurgy and in situ. The preparation of the composite are divided into four steps. Firstly, the pretreated silicon powder and alumina powder were mixed and ball milled under the protection gas of argon. Secondly, put the ball milled mixed powder into a mold, make the mold under the pressure of150MPa for5minutes, then get the raw material body from the mold. Thirdly, put the raw material body into tube furnace which were preheat under350℃for5min, than heat to720℃, stay warm at the temperature for3h. The last, after the body cool down, use the hot press to press the raw material body at the pressure of80MPa and at the temperature of350℃for10min. After hot pressing, the material is the Al2O3/Al-Si matrix composite.During the sintering processes, the alumina powder and silica powder are under the redox reaction.4Al+3SiO2=2Al2O3+3SiThe Si produced in the reaction was combined with alumina to form the aluminum silicon alloy substrate. The Al2O3powder were distributed in the substrate equally as the reinforcing phase, forming the reinforcing system in the composite. Compare with other composites preparations, this method enjoy some advantages. On one hand, the Al2O3particles produced in the composite preparation process, which were small and without contamination on their surface, could be combined with the matrix well. On the other hand, at a reasonable content of silica powder in the raw material, the SiO2in the body could be reduced by Al completely and generated reinforcing phase particles at the same time. The generated Si and Al combined to form alumina silica alloy, which can reinforce the matrix.The microstructure and morphologies of this composite were investigated by metalloscope, scanning electronic microscopy and XRD. The investigation shows that, the internal of the composite was the tissue made of alumina-silica matrix+Al2O3particles+pores, and the Al2O3reinforcing particles generated from in suit were distributed in the matrix uniformly along with the pores. The metal mechanic property, hardness and impact wear properties of this composite were tested by universal material testing machine, Brinell hardness tester and friction wear testing machine, showing that the compressive strength and the hardness increased first and decrease with the increasing content of silica powder. The strength of extension and ductility of the composite decreased with the increasing content of silica powder. The wear resistance increased with the increasing content of silica powder.The analysis of tensile fracture shows that the sources of crack were the primary porosity and surface between reinforcing phase and the matrix. The Al2O3particles were surrounded by alumina. As the silica content in the raw materialincreased, the fracture mechanism of this composite from interface layer ductile damage change into grain boundary brittle failure. The analysis of wear surface shows that in the impact wear testing, the alumina silica matrix was concaved by being impacted, while the Al2O3particles undertake the friction make less wear of composite. The hardness, the ability to resist adhesion and plough cut of the composite were increased as the increasing content of SiO2in the raw material.The aim of this study is to treat and use the waste cans and foundry dust in a recycling way. The preparation of composite is much more simple and reality than the way to extract pure alumina from waste cans. During the process of preparation, large amount of foundry dust were put into the raw material, giving a new way to recycle the foundry dust. The foundry dust in the raw material at the content of20%～40%, the compressive strength, hardness and wear-resistant of the composites which were made from these raw materials would be better than the pure alumina extracted from the waste cans. The density, hardness and wear-resistant were improved as the increasing content of SiO2in composites, while the strength of extension, ductility, plasticity and abrasion loss decreased. Based on the characters of particles reinforcing phase composites as well as the results of this study, this composite which were made in this study could be used in the material field required lightweight and wear-resisting.