Papers by Author: J.C. Huang

Abstract: Mg-based composites are fabricated through mechanical alloying (MA) the Mg65Cu20Y10Ag5 amorphous alloy spun and mixed with 1-5 vol.% spherical nano-sized ZrO2 particles in the planetary mill, after then formed by hot pressing in Ar atmosphere under different pressures at the temperature 5 K above the glass transition temperature (Tg). The microstructure characterizations of the resulting specimens are conducted by means of XRD, FEG-SEM, and TEM techniques. It is found that the nano-sized ZrO2 dispersed Mg-based composite alloy powders can reach to a homogeneous size distribution (about 80 nm) after 50-hour mechanical alloying. After hot pressing of these composite alloy powders under the pressure of 1100 MPa at 409K, a 96% dense bulk specimen can be formed. Throughout the MA and hot pressing, the amorphous nature of the Mg65Cu25Y10Ag5 matrix is maintained. The hardness of the formed bulk Mg-based composites (with 3 vol.% nano-sized ZrO2 particles) can reach to 370 in Hv scale. In addition, the toughness of the formed bulk Mg-based composites presents an increasing trend with the content of nano-sized ZrO2 particles and can reach to 8.9 MPa m .

Abstract: A series of Mg-based alloys with composition of Mg65Y10Cu25-XAgX, x = 0, 5, 10, were selected for investigating the microstructure evolution of the Mg-based nano/amorphous-composite alloy powder synthesized by the combination method of melt-spinning and mechanical alloying (MA). The microstructure characterization of the alloy powders was conducted by means of DSC, XRD, FEG-SEM, and TEM techniques. The result of XRD reveals that the entire as-quenched alloy ribbons exhibit a broaden diffraction pattern of amorphous phase. After 50 hours milling the mixture of amorphous alloy ribbons with 5 vol.% of nano-sized ZrO2 by planetary mill, the ZrO2 dispersed magnesium composite alloy powder can reach to a homogeneous size distribution. In parallel, the MA composite Mg-based alloy powders still remain an amorphous state by the characterization of X-ray diffraction and the DSC analysis. A clear Tg (glass transition temperature) and most wide supercooled region (about 44 K) were revealed for both the Mg65Y10Cu20Ag5 alloy ribbon and the MA magnesium composite powder. In addition, the result of TEM observation also revealed that the ZrO2 with average particle size of 80 nm distributed homogeneously in the amorphous matrix of the Mg65Y10Cu20Ag5 /5 vol.% ZrO2 composite alloy powder. The interface between the ZrO2 dispersoid and the amorphous matrix of the composite alloy powder exhibits a very good bonding condition.

Abstract: The current study applies the inclusion of thermally stable ceramic nano powders into the light weight AZ61 Mg base alloys via spray forming plus extrusion. The combination of spray forming and severe extrusion provides a new processing route for fabricating nano composites, with uniform distribution of the nano fillers. Parallel tries using the PM route followed by the same severe extrusion can also yield sound composites but the dispersion of the nano SiO2 appears to be less uniform. The processed composites are characterized in terms of microstructure examination, thermal analysis, phase identification, and mechanical testing.

Abstract: There have been numerous methods in fabricating particulate reinforced metallic matrix composites, including stir casting, squeeze casting, spray forming, powder metallurgy, and mechanical alloying. In this paper, one solid state processing technique, friction stir processing, is applied to incorporate 5-15 vol% nano-sized ceramic particles SiO2 into the AZ61 Mg alloy matrix to form bulk composites, using the characteristic rotating downward and circular material flow around the stir pin. The upper working FSP temperature is controlled to less than 400oC in order to avoid chemical reaction. The fixed pin tool is 6 mm in diameter and 6 mm in length, with a shoulder diameter of 18 mm and a 3o tilt angle. The advancing speed of the rotating pin is kept constant to be 45 mm/min, with rotational speed of the pin from 800 rpm (rotation per min), resulting in a strain rate around 101 s-1. After one-pass FSP, the particle dispersion within the central cross-sectional area of the onion ring regions, measuring nearly 6 mm in diameter, was macroscopically uniform. However, the observed particle size is frequently 0.5-5 µm, much larger than the individual SiO2 size (~20 nm), suggesting the clustering of nano particles. The situation after two FSP passes, with an opposite FSP direction for the second pass, appear to be further improved. Electron microscopy characterizations reveal that the aggregating particles were seen to vary from 10 to 1000 nm in size. Some of the large particles, 1-5 µm in diameter, were identified to be the Mn bearing dispersoids (e.g. Al4Mn) by the SEM-EDS. The average grain sizes of the composites with 5-15 vol% SiO2 varied within 00.5-2 µm, and the composites double the hardness as compared with the as-received AZ61 cast billet.

Abstract: The preparation of Mg49Y15Cu36 metallic glass composite powders was accomplished by mechanical alloying of pure Mg, Y, Cu, and WC powder mixture after 10 h milling. In the ball-milled composites, initial WC particles were homogeneously dispersed in the Mg-based alloy glassy matrix. The metallic glass composites powders were found to exhibit a large supercooled liquid region before crystallization. Bulk metallic glass composites were formed by vacuum hot pressing the as-milled WC/ Mg49Y15Cu36 metallic glass composite powders at 473 K in the pressure range of 0.72-1.20 GPa. BMG composite with submicron WC particles homogeneously embedded in a highly dense nanocrystalline/amorphous matrix was successfully prepared under pressure of 1.20 GPa. It was found that the applied pressure during consolidation could enhance the thermal stability and promotes nanocrystallization of WC/ Mg49Y15Cu36 BMG composites.

Abstract: The characterizations on the microstructural and mechanical properties of the Mg-Al-Zn multi-element intermetallic alloys fabricated by friction stir processing (FSP) are presented. The composites of the alloys vary within Mg35-70Al5-25Zn25-45. The maximum working temperature can reach 550oC. The current process applies the FSP on vertically stacked foils of various portions of Mg, Al and Zn, 99.9% in purity and 0.2 to 1 mm in thickness. In order to homogenize the alloy composition, three or more FSP passes in opposite directions are applied. Depending on the relative contents of Mg, Al and Zn, numerous intermetallic compound phases are induced. The resulting intermetallic alloys exhibit high hardness up to 350 Hv.

Abstract: The texture characteristics and the relationship between texture and tensile properties at room temperature and superplasticity at high temperatures in a hot extruded AZ61 alloy are examined in this paper. After warm extrusion, the alloy exhibits a of refined grains microstructure and a sharp basal {0001} texture. The tensile properties at room and elevated temperatures in extruded with the loading axis oriented at 0°, 45° and 90° to the extrusion direction are tested. It is found that the 45° specimens exhibit has lower yield strength and higher ductility. The possible causes for mechanical anisotropy are also analyzed based on the Schmid factor calculations.