Using nickel catalyst supported on aluminum powders, carbon nanotubes (CNTs) were successfully synthesized in aluminum powders by in-situ chemical vapor deposition at 650 °C. Structural characterization revealed that the as-grown CNTs possessed higher graphitization degree and straight graphite shell. By this approach, more homogeneous dispersion of CNTs in aluminum powders was achieved compared with the traditional mechanical mixture methods. Using the in-situ synthesized CNTs/Al composite powders and powder metallurgy process, CNTs/Al bulk composites were prepared. Performance testing showed that the mechanical properties and dimensional stability of the composites were improved obviously, which was attributed to the superior dispersion of CNTs in aluminum matrix and the strong interfacial bonding between CNTs and matrix.

MgAl₂O₄ particle-reinforced AC4C based alloy composites were fabricated by the stirring-casting method. The effects of the average sizes and the size distributions of MgAl₂O₄ particles on the dispersibility were investigated, and the microstructures, strength, and fatigue properties of MgAl₂O₄ particle-reinforced AC4C based alloy composites were evaluated. Tensile strength in the MgAl₂O₄ particle-reinforced AC4C based alloy composite was increased by using the classified particles. The fatigue limit at 10⁷ cycles in the MgAl₂O₄ particle-reinforced AC4C-Cu composite increased by 27% compared to the unreinforced alloy at 250 °C. Dislocations were observed in the matrix around the MgAl₂O₄ particle which resulted from the mismatch of thermal expansion coefficients between MgAl₂O₄ and Al, and resisted failure and caused fatigue cracks to propagate around the MgAl₂O₄ particles, resulting in extensive crack deflection and crack bowing, which contributed to the improvement of fatigue strength.

Al-Si-Fe based alloys are attractive light-weight structural materials for automotive engine components because of their high wear resistance, low density and low thermal expansion. Al-17Si-5Fe-2Cu-1Mg-1Ni-1Zr alloys were produced in compact form by a spark plasma sintering (SPS) technique using gas atomized powders. The mean grain size of the compact was 530nm, and fine equiaxed grains and uniformly distributed precipitates were observed in the compact. The compressive deformation behavior of the SPSed materials was examined at various temperatures and strain rates. All the true stress-true strain curves showed steady state flow after reaching peak stress. The peak stress decreased with increasing test temperature and decreasing strain rate. In the deformed specimens, the equiaxed grain morphology and the dislocation microstructure within the equiaxed grains were observed. These facts strongly indicated the occurrence of dynamic recrystallization during high temperature deformationof the present alloy.

Al-5%Si-Al₂O₃ composites were prepared by powdermetallurgy and in-situ reactive synthesistechnology. Friction and wear properties of Al-5%Si-Al₂O₃ composites were studied using an M-2000 wear tester. The effects of load, sliding speed and long time continuous friction on friction and wear properties of Al-5%Si-Al₂O₃ composites were investigated, respectively. Wear surface and wear mechanism of Al-5%Si-Al₂O₃ composites were studied by Quanta 200 FE-SEM. Results showed that with load increasing, wear loss and coefficient of friction increased. With sliding speed going up, the surface temperature of sample made the rate of the producing of oxidation layer increase, while wear loss and coefficient of friction decreased. With the sliding distance increasing, coefficient of friction increased because the adhesive wear mechanism occurred in the initial stage, then formation and destruction of the oxide layer on the surface of the sample tended to a dynamic equilibrium, the surface state of the sample was relatively stable and so did the coefficient of friction. The experiment shows that the main wear mechanism of Al-5%Si-Al₂O₃ composites includes abrasive wear, adhesive wear and oxidation wear.

The B₄C/2024Al composites were successfully produced by pressureless infiltration method, and the effects of heat treatment on phase content and mechanical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and mechanical properties testing. The results show that phases of B₄C/2024Al composites include B₄C, Al, Al₃BC, AlB₂ and Al₂Cu. The phase species remain unchanged; however, the phase content of the composites changes significantly after heat treatment at the temperature of 660, 700, 800 or 900 °C for 12, 24 or 36 h. It is found that the heat treatment results in not only considerable enhancement in hardness, but also reduction in bending strength of the composites. Heat treatment at 800 °C for 36 h does best to hardness of the composites, while at 700 °C for 36 h it is the most beneficial to their comprehensive mechanical properties.

Different proportions of commercial 2024 aluminum alloy powder and FeNiCrCoAl₃ high entropy alloy (HEA) powder were ball-milled (BM) for different time. The powder was consolidated by hot extrusion method. The microstructures of the milled powder and bulk alloy were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Mechanical properties of the extruded alloy were examined by mechanical testing machine. The results show that after BM, the particle size and microstructures of the mixed alloy powder change obviously. After 48 h BM, the average size of mixed powder is about 30 nm, and then after hot extrusion, the average size of grains reaches about 70 nm. The compressive strength of the extruded alloy reaches 710 MPa under certain conditions of milling time and composition. As a result of the identification of the nano-/micro-structure-property relationship of the samples, such high strength is attributed mainly to the nanocrystalline grains of α(Al) and nanoscaled FeNiCrCoAl₃ particles, and the fine secondary phase of Al₂Cu and Fe-rich phases.

This study was performed to investigate microstructure of dissimilar friction stir welds manufactured with AA6061-T6 and AZ31 alloy sheets. Dissimilar butt joints were fabricated under the ‘off-set’ condition that tool plunge position shifted toward AZ31 from the interface between AA6061-T6 and AZ31. Optimized tool rotating speed and its traveling speed were selected through a lot of preliminary experiments. Electron back-scatter diffraction (EBSD) technique was applied to measure texture in the stir zone (SZ). Grain size distribution and misorientation angle distribution were also obtained. A remarkably fine-grained microstructure was observed in the SZ. Randomized or weaker plane orientations were formed in the SZ of AA6061-T6, while rotated basal plane orientations were concentrated in the SZ of AZ31. Average size of recrystallized grains was measured as just 2.5-4.5 μm. The fraction of high-angle boundary in the SZ of AA6061-T6 increased and that of low-angle boundary in the SZ of AZ31 decreased compared with the base metals.

Carbon nanotubes (CNTs) reinforced aluminum matrix composites were fabricated by mechanical milling followed by hot extrusion. The commercial Al-2024 alloy with 1% CNTs was milled under various ball milling conditions. Microstructure evolution and mechanical properties of the milled powder and consolidated bulk materials were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and mechanical test. The effect of CNTs concentration and milling time on the microstructure of the CNTs/Al-2024 composites was studied. Based on the structural observation, the formation behavior of nanostructure in ball milled powder was discussed. The results show that the increment in the milling time and ration speed, for a fixed amount of CNTs, causes a reduction of the particle size of powders resulting from MM. The finest particle size was obtained after 15 h of milling. Moreover, the composite had an increase in tensile strength due to the small amount of CNTs addition.