Papers by Author: Dan Qing Yi

Abstract: microstructures, aging hardness, mechanical properties of Mg-9Gd-4Y-0.3Zr alloys were investigated. The microstructure is a typical dendritic structure of as-cast sample, The aging test of extruded samples were carried at a temperature rang of 200-300°C and at a different aging time. The aging peak hardness is about 120HV, tensile strength was tested at temperature 25°C, 200°C, 250°C and 300°C, tensile strengths are 375 Mpa, 364 Mpa, 329 Mpa, 286 Mpa respectively, the maximum elongation is 13.32% at 300°C. The fracture mode is mainly microvoid coalescence fracture combination the brittle cleavage fracture at room temperature, and microvoid coalescence fracture at 200-300°C.

Abstract: The exfoliation corrosion behavior of 2524 aluminum alloy was studied by Transmission Electron Microscope (TEM), hydrogen evolution and Electrochemical impedance spectroscopy (EIS) . The results showed that 2524 aluminum alloy was very susceptible to exfoliation corrosion and the exfoliation corrosion appeared after 24 h. EIS could better explain the exfoliation corrosion than hydrogen evolution. Exfoliation corrosion kinetics included accelerated formation of pitting, quick development of pitting, retarded formation of exfoliation and steady development of exfoliation.

Abstract: The microstructures and corrosion properties of AZ91 magnesium alloy with trace additions of Sc were investigated. The microstructures were observed by OM and SEM, and the corrosion properties were studied by electrochemical technique. The results show that the alloys with Sc form a second-phase Al3Sc, the grains become finer with the increasing content of Sc and the microstructure is the finest when Sc content up to 0.6%, the corrosion resistant of alloy combining with Sc is improved.

Abstract: The Mg-Zn-Zr alloy ZK60 with added trace rare-earth elements Y(0.9wt%) and Ce(0.9wt%) were prepared. After hot extrusion and aging treatment, the tensile mechanical properties of the alloys were tested at room temperature. Microstructures of the alloys were investigated by optical microscope (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The existing form, affecting mechanisms of trace Y and Ce in alloys and the effects on the microstructures and mechanical properties of ZK60 alloy were discussed. The results showed that: trace rare-earth elements Y and Ce both had remarkable grain-refining effects on the alloys, while the grain-refining effect of Y was more significant than that of Ce. RE elements Y and Ce improved the mechanical properties of the ZK60 alloy, but the strengthening effect of Y was more remarkable. It was found that σb of Mg-Zn-Zr-Y alloy was improved by 12.6％. Addition of Ce to the ZK60 alloy led to an increase in ductility of the alloy from 15% to 17%.

Abstract: Mechanical alloying(MA) technique and single-roller melt spinning technique were used to prepare Fe86Zr5.5Nb5.5B3 nanocrystalline and amorphous powders, bulk alloys were prepared by cryogenically high-pressure quick sintering. The results showed that: (1) after MA process for 15 hours, the grain size of α-Fe phase was ≤10nm; (2) melt spinning powders were fragmented by ball milling, but remained amorphous state. The crystallization temperature of this amorphous powder was about 500°C. Apparent activation energy of the amorphous crystallization was E=294.1KJ/mol; (3) under the quick sintering conditions of P=5.5GPa/t=3min/Pw≥1050W, single phaseα-Fe nanocrystalline(8～15nm) bulk alloys with relative density≥98.7% can be obtained.