Abstract: In this study, the effects of B4C and SiC particle reinforcements on wear properties of magnesium matrix metal composites produced by pressure infiltration method were investigated. AZ91 (9%Al-1%Zn) magnesium alloy was used as a matrix. AZ91 magnesium alloy was melted under an argon atmosphere. The melt was infiltrated to the particles with an appropriate pressure. Wear tests, hardness tests were performed respectively. Microstructure characterizations were examined by light optical (LOM) and scanning electron microscope (SEM). The results showed that uniform particle distributions were achieved in both B4C and SiC reinforced composites. Wear behaviors of magnesium matrix metal composites changed as a function of type of particles. SiC reinforced composite has better wear performance and higher hardness than B4C reinforced composite.
Abstract: Microstructure and mechanical properties of AZ91D
Mg alloys for nonflammable use, containing Ca and Y, were
investigated in this study. Solid solution treatment of AZ91D Mg alloy
with Ca and Y was successfully conducted at 420oC and
supersaturated microstructure with almost all beta phases resolved into
matrix was obtained. After solid solution treatment, the alloy was
annealed at temperatures of 180 and 200oC for time intervals from 1
min to 48 hrs and hardness of each condition was measured by
micro-Vickers method. Peak aging conditions were deduced from the
results as at the temperature of 200oC for 10 hrs. Hot rolling was also
carried out at 400oC by the reduction ratio of 0.6 through 5 passes
followed by recrystallization treatment. Tensile and compressive
properties were measured at room temperature on the specimens of
each process, i.e. as-cast, solution treatment, hot rolling, and
recrystallization.
Abstract: The use of magnesium alloys is limited due to their
susceptibility to corrosion although they have many attractive
physical and mechanical properties. To increase mechanical and
corrosion properties of these alloys, many deposition method and
coating types are used. Electroless Ni–B coatings have received
considerable interest recently due to its unique properties such as
cost-effectiveness, thickness uniformity, good wear resistance,
lubricity, good ductility and corrosion resistance, excellent
solderability and electrical properties and antibacterial property. In
this study, electroless Ni-B coating could been deposited on AZ91
magnesium alloy. The obtained coating exhibited a harder and
rougher structure than the substrate.
Abstract: To develop AZ91D magnesium alloys with improved
properties, we have applied TiN and VN/TiN multilayer coatings
using DC magnetron sputter technique. Coating structure, surface
morphology, chemical bonding and corrosion resistance of coatings
were analyzed by x-ray diffraction (XRD), scanning electron
microscope (SEM), x-ray photoelectron spectroscopy (XPS), and
tafel extrapolation method, respectively. XPS analysis reveal that VN
overlayer reacts with oxygen at the VN/TiN interface and forms more
stable TiN layer. Morphological investigations and the corrosion
results show that VN/TiN multilayer thin film coatings are quite
effective to optimize the corrosion resistance of Mg alloys.
Abstract: Phase equilibria of AZ91D Mg alloys for
nonflammable use, containing Ca and Y, were carried out by using
FactSage® and FTLite database, which revealed that solid solution
treatment could be performed at temperatures from 400 to 450oC.
Solid solution treatment of AZ91D Mg alloy without Ca and Y was
successfully conducted at 420oC and supersaturated microstructure
with all beta phase resolved into matrix was obtained. In the case of
AZ91D Mg alloy with some Ca and Y; however, a little amount of
intermetallic particles were observed after solid solution treatment.
After solid solution treatment, each alloy was annealed at temperatures
of 180 and 200oC for time intervals from 1 min to 48 hrs and hardness
of each condition was measured by micro-Vickers method. Peak aging
conditions were deduced as at the temperature of 200oC for 10 hrs.
Abstract: Tensile specimens of nonflammable AZ91D Mg alloy were fabricated in this study via cold chamber die-casting process. Dimensions of tensile specimens were 25mm in length, 4mm in width, and 0.8 or 3.0mm in thickness. Microstructure observation was conducted before and after tensile tests at room temperature. In the die casting process, various injection distances from 150 to 260mm were employed to obtain optimum process conditions. Distribution of Al12Mg17 phase was the key factor to determine the mechanical properties of die-cast Mg alloy. Specimens with 3mm of thickness showed superior mechanical properties to those with 0.8mm of thickness. Closed networking of Al12Mg17 phase along grain boundary was found to be detrimental to mechanical properties of die-cast Mg alloy.
Abstract: This study was aimed for investigating of
manufacturing high aluminum content Mg alloys using a horizontal
twin roll caster. Recently, weight saving has been key issues for lighter
transport equipments as well as electronic component parts. As
alternative materials to aluminum alloys, developing magnesium alloy
with higher strength has been expected. Normally high Aluminum
content Mg alloy has poor ductility and is difficult to be rolled because
of its high strength. However, twin roll casting process is suitable for
manufacturing wrought Mg alloys because materials can be cast
directly from molten metal. In this study, manufacturing of high
aluminum content magnesium alloy sheet using the roll casting
process has been carried out. Effects of manufacturing parameter, such
as roll velocity, pouring temperature and roll gap, on casting was
investigated. A microscopic observation of the crystals of cross section
of as cast strip as well as rolled strip was conducted.