Papers by Author: Qiu Lin Li

Abstract: In this work, the microstructure evolution of as-cast NAB under different electropulsing parameters were studied. The microstructure of the electropulsing treatment (EPT) sample was characterized by mircohardness test and optical microscopy. The results show that compared with heat treatment, when the peak current density reaches 5.84×10⁸A/m² (no significant change in the structure when the peak current density is lower), the β' phase region undergo phase transition in a shorter time. When the peak current density reaches 7.25×10⁸A/m², the sample is significantly affected by the Joule heating effect, and the κ_Ⅲ and κ_Ⅳ phases are successively dissolved to form Widmanstätten α structure. As the β' phase increases and the Widmanstätten α structure forms, the hardness value of the microstructure increases by 80%.

Abstract: The paper introduces a new method to produce large sized Al-B₄C-Al₂O_3np composites, which combines ball milling to prepare Al₂O_3np/Al mixed powder and semi-solid casting to contribute the injection of Al₂O_3np/Al mixed powder into the melt. The deformation performance of Al₂O_3np and micro-Al through ball milling with different Al/Al₂O_3np ratios, different milling time and different balls were studied respectively. It was revealed that micro-Al particles were milled from twisted and crimpled foil pieces to shuttles with Al₂O_3np embedded on it through 4h milling with 10mm balls. And we consider it as the best bonding between Al₂O_3np and micro-Al we could attain. And a plate of 25kg of Al-B₄C-Al₂O_3np composite was fabricated successfully with the injection of the Al₂O_3np/Al mixed powder. Spherical Al₂O_3np of 300nm and needle-like TiB₂ with 200nm in radius and 800nm-4μm in length were found in SEM photographs. Tensile properties of Al-B₄C-Al₂O_3np composites were tested at room temperature and high temperature. It was showed higher mechanical properties than Al-B₄C composites at room temperature and elevated temperature. Particularly, a 40% increase of UTS of Al-15wt.% B₄C-1wt.%Al₂O_3np at 350°C was observed.

Abstract: B₄C/Al composite was a promising neutron absorb material. In this work, B₄C/Al composite sheets were asymmetrically rolled and annealed. The asymmetric (ASR) condition was introduced by applying mismatched roll diameters with diameter ratios of 1.1, 1.2 and 1.3, respectively., while the symmetric rolling (SR) was used as the control experiment. Mechanical properties and microstructures of the composite were tested after cold rolling and annealing. Results showed that: ASR with small diameter ratio decreased the texture volume fraction in the B₄C/Al composite, but when diameter ratio of ASR reached 1.3 new slip systems were actuated and the texture volume fraction started to increase. The average grain size of the aluminium matrix was smaller after ASR, and it decreased with the increasing diameter ratio. The hardness of B₄C/Al composite after ASR was about 40% higher than the one rolled by symmetric rolling, proved that ASR is a promising way to enhance the properties of B₄C/Al composite.

Abstract: Alternating traveling magnetic field (TMF) was introduced to agglomerate the inclusions with a density smaller than surrounding melt. Primary silicon particles precipitating from the solidification process of hypereutectic Al-Si alloy was regarded as inclusions need removing. Results indicated that alternating TMF was more effective to promote the inclusions to agglomerate into clusters than downward TMF. The effect of alternating TMF to agglomerate the inclusions increases with the increase of current and frequency. There exists the best alternating time to get the best agglomeration effect. In this study, 10s is the best alternating time.

Abstract: A series of Al-Si hypoeutectic alloy ingots were prepared by centrifugal casting (CC) both with and without an external electromagnetic field (EMF). The effects the EMF on grain refinement and on the solidification mechanism during centrifugal casting have been investigated using optical microscopy, scanning electron microscopy (SEM) and electron backscattering diffraction (EBSD) orientation measurements. The electromagnetic stirring effect caused by the EMF promotes the columnar-equiaxed transition (CET) resulting in a finer cast grain size. The silicon and aluminum nucleate and grow independently both with and without EMF