| Under the background of the spacecraft structure, carbon fiber reinforced aluminum matrix composite with new high specific strength, high specific stiffness was developed. Composites with carbon fiber volume fraction of 60% and matrix of Al-XMg alloy were successfully prepared by pressure infiltration method in this paper. By using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution electron microscopy (HREM), energy dispersive spectroscopy (EDAX), Brinell durometer and tensile machine, microstructure, interface structure and formation mechanism of composite materials were investigated. In addition, mechanical and corrosion properties of composite materials were tested, and related factors were analyzed.Composition of matrix alloy in composite was designed to reveal the effect of Mg element on the structure, microstructure of the interface, and mechanical properties of composites.In order to investigate the infiltration principle of carbon fiber reinforced aluminum matrix composites, the vacuum sessile drop method was used to analyze the wetting behavior between matrix alloy and two-dimensional carbon fibers. With the addition of Mg element in the aluminum matrix, the wetting angle between aluminum and fiber can be reduced. When the Mg element was added to 13 wt.%, the wetting angle decreased faster, which indicated that the wettability between them was better. The minimum pressure to prepare composites with pressure infiltration method can be directly calculated by the variation of wetting angle and it can guide the preparation of composites.Mg segregated at the interface of Cf/Al-Mg composite, which resulted in the change of precipitation behavior at the interface. With the increase of Mg, amount of Al4C3 phase decreased and even disappeared at the interface, while metastableβ′(Al3Mg2) phase generated at the interface and in the grains. Transformation of metastableβ′(Al3Mg2) phase to stableβ(Al3Mg2) phase is difficult due to the introduction of a large number of interfaces and variation of precipitation condition. Mechanical properties of composites were greatly improved with the increase of Mg in matrix alloy. When Mg content was added from 0 to 8.5 wt.% in composite, the bending strength can be increased sharply from 425 MPa to 1350 MPa. However, when Mg content was added from 8.5 to 17 wt.% in composite, the bending strength can only be increased slightly from 1350 MPa to 1500MPa. Variation of fracture from flat fractography to a large number of fibers pulled out indicated that moderate sticky point of composite interface can effectively improve work of fracture. In the Cf/Al-Mg composites, the increase of Mg in matrix alloy can greatly reduce the corrosion property of composites.Nd was easier to segregate partially than Mg at the interface of Cf/Al-17Mg-Nd composites. A lot of nano-scaled Al11Nd3 phase precipitated at the interface of the composites. Because of the non-uniform distribution of Nd, there existed no Nd in some areas, which resulted in the direct contact of Al and carbon fiber and the generation of a certain amount of brittle phase Al4C3 at the interface. With the increase of Nd element, UTS of composites significantly declined from 1500MPa to 800MPa. But it had little influence on the elastic modulus of composites. |
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