Guangchun Yao

Influence of Mg Addition on Graphite Particle Distribution in the Al Alloy Matrix Composites

Al alloy matrix composites reinforced with copper-coated graphite particle have been prepared by melt stirring process in this work. The effect of the addition of Mg on distribution of the graphite particles has been investigated. Scanning electron microscopy (SEM) was used to observe the micro-morphology of Al alloy matrix composites reinforced with graphite particles. Meanwhile, the content of graphite was analyzed in the different position of casting by dissolution method and the mechanical properties of the composites were detected. The results show that the content of graphite increase with increasing Mg content; the graphite particles distribute uniformly in the particle reinforced metal matrix composites (PMMC) with 0.6 wt pct Mg; however, the agglomeration of the graphite particles is observed obviously in the matrix when Mg content is more than 1.0 wt pct. In addition, the proper Mg addition amount is beneficial to enhance the mechanical properties of the graphite particles reinforced Al alloy matrix composites and the abrasion resistance of the materials due to a reduce friction coefficient.

Effect of Nanopowder Content on Properties of NiFe2O4 Matrix Inert Anode for Aluminum Electrolysis

Two-step sintering process was adopted to prepare NiFe2O4 matrix inert anode for aluminum electrolysis in this research. In the process of synthesizing NiFe2O4 spinel, Fe2O3 and NiO powders as raw materials added additives were synthesized at 1000 °C for 6h. Through crushing and screening, adding NiFe2O4 nanopowder, particle gradation and compression molding, the nickel ferrite matrix ceramic inert anode was sintered secondarily at 1300 °C for 6h. The effect of NiFe2O4 nanopowder content on the density and porosity, bending strength and impact toughness was investigated in details. The results showed the addition of NiFe2O4 nanopowder had considerable influence on the properties of NiFe2O4 matrix ceramic inert anode. Inert anodes had the best comprehensive properties while adding 30 wt% nanopowder. The values of density and porosity were 4.86 g/cm3 and 3.5% respectively, the value of bending strength was 42.47 MPa and the value of impact toughness was 3.31 J/cm2.

Interface Evolution in the Process of Fabricating Aluminum Foam Sandwiches

Aluminum foam sandwiches (AFS) which have the properties of high impact strength, efficient capacity of energy dissipation, high damping and thermal insulation, were obtained by combining steel face sheets with a lightweight closed-cell aluminum foam core. The steel sheet was hot-dipped in pure aluminum and the precursor was prepared by powder metallurgy method. The precombination of the precursor and the hot-dipped steel sheet was carried out by using hot-pressing technology. The three-layer composite was baked rapidly in a furnace to fabricate AFS. It was found that the steel sheet coated by pure aluminum combined very well with the precursor by hot-press. Then the further diffusion was promoted in the foaming process. The boundary of the AFS which was between the foam core and the face sheet had a high strength by diffusion bonding. Simplified theoretical diffusion model was introduced to explain the evolution of the boundary in the hot-pressing process.

Effect of MnO2 Addition on Early‐Stage Sintering Behavior and Properties of NiFe2O4 Ceramics

The samples with small amounts of MnO2 (0, 0.5, 1.0, 2.5 wt%, respectively) were prepared via ball-milling process and two-step sintering process from commercial powders (i.e. Fe2O3, NiO and MnO2). Microstructure features, phase transformation, the early-stage sintering behavior and mechanical properties of Mn-doped NiFe2O4 samples have been investigated. Results indicate that the reduction of MnO2 into Mn2O3 and following the reduction of Mn2O3 into MnO existed in sintering process. No new phases are detected in the matrix, the crystalline structures of ceramic matrix are still NiFe2O4 spinel structure. MnO2 addition can promote the sintering process. The temperature for 1 wt% MnO2-doped samples to reach the maximum shrinkage rate is 59 °C lower than that of un-doped samples.

Energy Absorption of Aluminum Foam-Filled Tubes under Quasi-Static Axial Loading

Closed aluminum foams fitted thin-walled circular tubes was investigated for its energy absorption characteristics. Compression test was carried out to obtain the representative quasi-static stress-strain curves. The deformation characteristic (foam, tube and their combination) was analyzed. The results indicated that the deformation mode of aluminum foam and tube changed after combine. Foam-tube configuration absorbed more energy than the sum of foam and tube due to the interaction between tube and filler which contains friction, extrusion, crack formation and growth. In addition, the energy absorption of foam-tube configuration was 6 times of aluminum foams. The experiment results reflected that the foam-tube configuration was a potential energy absorber candidate for car industry and transportation cask.