Preparation And Wear Resistance Of In-situ Al₂O₃ Reinforced Al-Si Matrix Composites By Adding SiO₂

In recent years,because of the advantages of high strength,low coefficient of thermal expansion,and good heat resistance and wear resistance of in-situ Al₂O₃ particle reinforced aluminum matrix composites,it has become a new type of material that has been the focus of attention in various fields.At present,the research on in-situ Al₂O₃ particle reinforced Al-Si matrix composites mainly focuses on hypoeutectic and eutectic Al-Si alloys,but the research on the preparation of hypereutectic Al-Si alloys is rare.In this paper,the melt reaction method was used to prepare in-situ Al₂O_3?p?/Al-20Si composite materials.The effect of the addition of Si O₂ powder on the in-situ reaction was discussed.The best process parameters in the preparation process were determined,and under the best process parameters composite materials were prepared with adding different amounts of SiO₂.The microstructure and properties of the composite materials were studied using scanning electron microscope?SEM?,X-ray diffraction?XRD?,Vickers hardness tester,universal tensile testing machine and reciprocating friction and wear tester.The results show that method of the SiO₂ powder addition is improved:The SiO₂powder floats up when the aluminum foil-wrapped powder addition method is used,the preformed block can not be melted when the preform addition method is used.And the SiO₂powder is added at the semi-solid temperature range can produce Al₂O_3?p?/Al-20Si composites with good Al₂O₃ particle distribution and excellent performance.The process parameters for obtaining good dispersion of Al₂O₃ particles with the self-designed three-paddle stirring blade are followed:the stirring speed is 800r/min,and the stirring time is 10 min.The Al₂O₃ particles generated in the Al₂O_3?p?/Al-20Si composite are mainly distributed at the boundary of the primary Si,which can significantly inhibit the growth of the primary Si.As the amount of SiO₂ added increases,the primary Si size decreases from160-180?m to 40-65?m.Mechanical properties of composite materials under different SiO₂additions:With the increase of SiO₂ additions,the hardness of composites increased from60.19HBW to 86.69HBW,and the tensile strength increased from 102MPa to 148MPa.The hardness and tensile strength are the best when the added amount is 5wt.%,which is obviously improved compared with the base alloy.Friction and wear results show that:The friction coefficient and wear of composite materials decrease with the increase of SiO₂addition.The wear resistance of composite materials gradually improves.The main wear mechanism gradually changes from adhesive wear to abrasive wear.When the addition amount is 5wt%,the wear resistance of the composite material is the best.However,as the load increases,the wear resistance of the composite material decreases significantly.The main wear mechanism changes from abrasive wear to adhesive wear,especially when the applied load reaches 20N,the composite wears sharply.In the hypereutectic Al-20Si alloy,if the primary Si size is smaller and the distribution is more uniform,the overall performance of the alloy is better.Because the in-situ Al₂O₃particles can effectively refine the primary Si in the microstructure through the combination of heterogeneous nucleation and growth inhibition,and the generated Al₂O₃ particles can be evenly distributed,the hardness,strength and wear resistance of the composite material are improved.The content of Al₂O₃ particles generated by the reaction is the main factor affecting the performance of the composite.