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Al-60wt.%Si composites were successfully prepared by semi-solid squeezing powder mixture of Al and Si at 700 °C. The appearance of about 50wt.% Al-Si metal liquid results that less than 4–5 MPa pressure can squeeze the Al-Si powder mixture to near full density at vacuum condition. The effects of Si particle size on the microstructure and properties of Al-60wt.%Si were investigated. The results show that the composites are consisted of only Si and Al. Si particles distribute evenly in aluminum matrix. Al matrix exhibits a certain preferred orientation under the condition of directional solidification. Si particles with 5 μm size tend to be aggregated into locally interconnected particles and can be effectively passivated. As Si particle size ranges from 10 to 20 μm, the corner passivation effect for Si particles is gradually suppressed. The fracture morphology of Al-60wt.%Si is composed of cleavage platforms of Si grains and fine tearing ridges of Al which tightly wraps Si grains. With the increase of Si particle size from 5 to 20 μm, the flexural strength of Al-60wt.%Si decreases from 270 MPa to 223 MPa, the thermal conductivity increase from 128 to 136 W·m−1·°C−1, and the average coefficient of thermal expansion from ambient temperature to 400 °C ranges from 9.49 to 9.97 × 10−6 °C−1.

Copper based composites with high graphite contents for pantograph sliders have been manufactured via an inexpensive powder metallurgy method. Large size cluster graphite is added into the matrix as solid lubricant to optimize the mechanical and wear performance of the composites. The mechanical performance and microstructure of graphite cluster/ copper-based (GC/Cu) composites are investigated. The highest graphite content in GC/Cu composites can reach up to 5 wt%. The graphite cluster/copper-based composites show an outstanding mechanical performance, in which the impact toughness can reach 4.8 J/cm2 with 5 wt% graphite cluster. The matrix is constituted with single α-phase Cu10Sn3with second phase particles CuNi2Sn. Moreover, friction and wear behavior with or without electric currency have been explored systematically, which indicates that the friction coefficient with 5 wt% graphite composites reached a minimum of 0.184 at a load of 25 N. It also exhibits the excellent friction performance under the effect of electric current. The smallest wear rate of 4.2×10−3 mg/m occurs in the sample with 2 wt% graphite at 30 A. Meanwhile, the interaction between pantographs and contact wire has been investigated based on elemental analysis and surface morphology. Oxidation and material transfer is found on the worn surface.

In this paper, high-Si reinforced Al matrix composites (H-Si/Al) with Si mass ratio 50–70% were successfully fabricated from the powder mixture of Si and Al by a novel route called as powder semi-solid squeeze. It is found that no Al–Si lamellar eutectic in the composites. As the Si content increases, fine Si particles in the H-Si/Al are reduced and the coarse Si particles may increase in size, or gather together to form twisted large particles and even form a space network structure. With the Si content ranging from 50% to 70%, The flexural strength varies between 248 and 179 MPa, the mean coefficient of thermal expansion from ambient temperature to 100 °C can be regulated between 11.32 and 7.55 × 10 −6 °C −1 , and the thermal conductivity varies between 140 and 120 W m −1 °C −1 , showing that H-Si/Al prepared by powder semi-solid squeeze have excellent mechanical and thermal properties.

Commercial F500 SiC powder and 6061 Al powder were chosen to fabricate the 50 vol.-% SiCp/6061Al composites via pressureless sintering. Effects of pre-treatment of the SiC powder and sintering temperature on the microstructures and properties of the composites were studied. Densification mechanism and interfacial reaction of the composites were also investigated. The results show that the composites have a high sintering ability and a low interfacial reaction activity. The density, bending strength and thermal conductivity of the composites are all sensitive to the sintering temperature. The composites sintered at 680°C are nearly fully dense and have the following optimal properties: the relative density of 98.5%, the bending strength of 495 MPa, the TC of 153 W/(m K) and the coefficient of thermal expansion of 8.1 × 10−6/°C (50–100°C), which are superior to most of the SiCp/Al composites of the similar composition reported previously.

High-performance copper-based pantograph slide materials play a crucial role in the rapid development of modern urban rail transit urgently. Herein, a full density graphite/copper-alloy matrix composite for pantograph slide has been successfully obtained by the hot powder forging process. The composite exhibits the full density when forging energy density is 307.6 J cm−3. In addition, the influence of different aging treatments on microstructure and mechanical performances of the composite has been studied in detail. The hardness and resistivity of the forged materials are greatly improved after an optimum aging treatment. Simultaneously, the friction and wear performances with or without currency current have been investigated, which demonstrates the friction coefficient can reach the minimum of 0.109 under 35 N. In current-carrying friction, the wear rate of the composite is an extremely small value of 5.5 × 10–5 mg m−1 after the aging treatment, indicating the outstanding anti-friction and self-lubricating performance. All the comprehensive analyses illustrate the full density graphite/copper-alloy matrix composite with excellent mechanical shows an enormous potential for pantograph slide.

SiC/Al composites with uniformly distributed SiC particles were fabricated by pressureless infiltration of liquid AlSi7Mg alloy into SiC preforms with different porosity derived from SiC powders. The linear expansion of SiC preforms without any deformation was about 4% due to the oxidation of SiC powders during the sintering process. SiC preforms had no change in both shape and dimensions after infiltration so that near-net-shape composites were achieved. As SiC volume fraction varies from 39% to 62%, the thermal conductivity of SiC/Al composites with bending strength beyond 360 MPa and elastic modulus beyond 140 GPa varies from 146 to 118 W m−1 K−1 at room temperature, and the mean linear coefficient of thermal expansion from room temperature to 373 K varies from 10 × 10−6 to 7.69 × 10−6 K−1, agreeing better with the Turner's model.