Feng Mao

Microstructure, mechanical properties and wear behaviour of Zn–Al–Cu–TiB2 in situ composites

Abstract Zn–Al–Cu–TiB 2 (ZA27–TiB 2 ) in situ composites were fabricated via reactions between molten aluminum and mixed halide salts (K 2 TiF 6 and KBF 4 ) at temperature of 875 °C. The microstructure, mechanical properties and wear behavior of the composites were investigated. Microstructure analysis shows that fine and clean TiB 2 particles distribute uniformly through the matrix. The mechanical properties of the composites increase with the increase in TiB 2 content. As TiB 2 content increases to 5% (mass fraction), an improvement of HB 18 in hardness and 49 MPa in ultimate tensile strength (UTS) is achieved. The overall results reveal that the composites possess low friction coefficients and the wear rate is reduced from 5.9×10 −3 to 1.3×10 −3 mm 3 /m after incorporating 5% TiB 2 . Friction coefficient and worn surface analysis indicate that there is a change in the wear mechanism in the initial stage of wear test after introducing in situ TiB 2 particles into the matrix.

Effect of homogenization annealing on microstructure, composition and mechanical properties of 7050/6009 bimetal slab

Abstract Homogenization annealing of the 7050/6009 bimetal slab prepared by direct-chill casting was investigated and its effects on microstructural evolution, composition distribution and mechanical properties in the interfacial region of the bimetal were studied. The results show that the optimized homogenization annealing process was 460 °C for 24 h. After homogenization annealing, the Zn-rich phases and Al 15 (FeMn) 3 Si 2 phases were precipitated at the interface of the bimetal. The diffusion layer thickness of homogenized bimetal increased by 30 µm from 440 to 480 °C for 24 h, while it increased by 280 µm from 12 to 36 h at 460 °C. The Vickers hardnesses at 6009 alloy side and interface of the bimetal decreased after homogenized annealing and grain coarsening was considered as the dominating softening mechanism. The hardness variation at 7050 alloy side was complicated due to the combined action of solution strengthening, dispersion strengthening and dissolution of reinforced phases.

Characteristics evolution of 6009/7050 bimetal slab prepared by direct-chill casting process

Abstract 6009/7050 alloy bimetal slab was prepared by a direct-chill (DC) casting process. Homogenizing annealing, hot rolling and T6 treatment were successively performed and their effects on microstructure and properties of the slab were studied. The results reveal that the average diffusion layer thickness of as-cast slab, determined by interdiffusion of elements Zn, Cu, Mg and Si, was about 400 µm. Excellent metallurgical bonding was achieved because all tensile samples fractured on the softer 6009 alloy side after homogenizing annealing. After homogenizing annealing plus rolling, the average diffusion layer thickness decreased to 100 µm, while the network structure of 7050 alloy side transformed to dispersive nubby structure. Furthermore, subsequent T6 treatment resulted in diffusion layer thickness up to 200 µm and an obvious increase of the Vickers hardness for both 7050 and 6009 sides. The layered structure of the as-cast 6009/7050 bimetal is retained after hot rolling and T6 treatment.