Study On Fabrication Of AlFeSiM Reinforced Al Matrix Composites By Means Of Reactive Infiltration

The pressureless infiltration technique means that metal liquid infiltrate into preform spontaneously by capillary, metal matrix composites are produced finally. At the same time there are reactions between elements. This technique offers the potential to be an alternative, simple, low-cost processing route for the manufacture of near-net shape silicon carbide reinforced aluminum matrix composites. But it also has many disadvantages, such as the poor wetting between ceramic and metal, under the atmosphere protect of N₂ or Ar, the long time and low rate of infiltration, the difficult control of volume fractions of ceramic particulates, and so on. Therefor, many works should be done to research infiltration mechanism, reduce limited conditions, improve atmosphere, get better Microstructure finally.The major research purpose is to simplify the pressureless infiltration process. Making pressureless infiltration happen under air condition, and the process happen rapidly, at the same time, studying effect of modifier and alloy on microstructure of AlFeSi /Al composite, get fine intermetallic reinforced Al matrix composites at last. The major research efforts of the present study are as follows: (1) The result showed that the microstructure of AlFeSi/Al composites are modified effectively via the addition of RE elements, the microstructure needle like reinforced phase are changed to polygon, furthermore, according to the different microstructure attained via the vary heating time from 10 minute to 30, the growth manner model of the reinforced phase modified was found. After the modified composites processed by solid solution, the microstructure of the reinforced phase was not changed effectively, but the dendrite crystals was passivated. The microstructure like"sea hedgehog"was found, via the addition of P-Cu alloy, at the same time, the AlFeSi reinforced phase and primary silicon phases were refined;(2) The microstructure needle like reinforced phase are changed to polygon, by adding nickel elements to the iron powder infiltrated. When the content ratio of nickel to iron is low, the reinforced phase is mostly Al5FeNi, furthermore, the stabilization of the phase is not well. When the Ni/Fe value is between 1:1 and 1:2, the rupturing effect is obvious; But with the Ni/Fe value increasing, the microstructure of AlNi3 phase are changed from polygon to strip. Besides, needle like reinforced phase are changed to polygon, via adding vanadium elements to the iron powder infiltrated. Via adding nickel and vanadium elements to the iron powder infiltrated, the rupturing effect is more obvious, and the reinforced phase are mostly Al5FeNi and NiV3;(3) Via adding titanium and vanadium elements to the iron powder infiltrated, the microstructure of Fe cis hexagonal with heating 20 minute, and the shape is island chain with heating 30 minute, more obvious. The reinforced phase are mostly the AlFeSiV compound, and the thin VSi phase distribute among the AlFeSiV compound. When adding boron elements and titanium elements to the iron powder infiltrated, the reinforced phases like polygon are packeted by the TiB2 phase and Ti5Si4 phase which block the diffuse between the reinforced phase and the melt alloy, accordingly the growth of the reinforced phase is restrained;(4) It was found that the microstructure"peach-core-like"often appear at the bottom of the infiltrating layer or when the size of infiltrating powder is big, at the same time the microstructure"peach-core-like"is easily founded when the process is puting alloy on loose bed or not casting alloy. The result showed the forming mechanism of the reinforced phase is solid-liquid interface reaction, also the growth mechanism model of the microstructure"peach-core-like"was ascertained; (5) The hardness of composites increased greatly compared with Al-13Si especially on the surface. The material shows great wear resistance because there are many reinforcements in the surface of composites. The wear resistance of the composites infiltrated Fe powder and RE modifier enhanced 0.6 in comparison with Al-13Si; The composites infiltrated Fe powder and Ni enhanced 1.6; the composites infiltrated V-Fe powder enhanced 1.9; The composites infiltrated B-Fe powder and Ti powder enhanced 2.1 in comparison with Al-13Si.In a word, the present study not only changed the character and structure of microstructure on AlFeSiM/Al composite, but also enhanced the mechanical properties and wear resistance, which have instructing significance for industrial application of the composite.