Papers by Author: Li Hui Chen

Abstract: In this study, stellite 6 alloy was overlaid on spheroidal graphite (SG) cast irons with various carbon contents (1.5wt%~3.8wt%) and a fixed silicon content (approximately 2.5wt%) using the plasma transferred arc (PTA) process at different overlaying current (140A~220A) while the travel speed of the PTA torch was maintained constant. Results indicated that the solidification structures of the stellite 6 overlayers were dendritic and had a large amount of interdendritic precipitates (M7C3 and M23C6 carbide) after the satellite 6 alloy had been overlaid on SG cast irons with different carbon contents (1.5wt%~3.8wt%) at a low overlaying current (I=140A). The partially melted zones of the substrates below the carbide-containing interfacial layers consisted of eutectic carbides (ledeburites) and fine pearlites. The amount of the carbide-containing interfacial layers and ledeburites increased following the increase in the overlaying current. The results of the tearing test reported that the occurrence of the carbide-containing interfacial layers was detrimental to the bonding strength between the overlayers and the substrates. The metallography of the fractured area of the tearing specimens after the bonding strength test revealed that fractures always occurred at the carbide-containing interfacial areas. On the other hand, the overlayers were rich in iron content when the overlaying currents were high (I=190A and 220A). Owing to the dilution effect, the matrices of the overlayers were α-Fe with lamellar M7C3 carbides. The results of the tearing test indicated that the bonding strength of the overlaid specimens was relatively low, and fractures always occurred in these highly diluted overlayers.

Abstract: Both Al-Zn alloy and Mg-Al-Zn alloy have been considered as high damping and light materials. For practical use, this study investigated the effects of the structure and the composition on the vibration fracture characteristics of the Al-xZn alloy and the Mg-xAl-Zn alloy under resonance. For Al-xZn (x=7, 11, 49, 83wt%) alloys, under both constant force and initial-deflection conditions, the 7Zn showed the greatest vibration life. For Mg-xAl-Zn (x=3, 6, 9wt%) alloys, experimental results indicate that the AZ31-F as-extruded samples showed a greater vibration life, while high Al fully-annealed samples (AZ91-O) had greater vibration fracture resistance under constant force conditions.