Y.H. Zhu

Tensile deformation and phase transformation of furnace-cooled Zn–Al based alloy

Abstract Phase transformation and microstructural changes of the furnace-cooled (FC) eutectoid Zn–Al based alloy were studied during thermal ageing and tensile deformation using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Two types of decomposition of Zn-rich phases η FC ′ and e were detected in both the aged and the tensile deformed alloy specimens. Precipitates of α and T′ phases were distinctly observed inside the light contrast η FC ′ and e phases, respectively, using back-scattered electron imaging. Under tensile deformation at 150°C, the coarse lamellar structure was deformed into fine particulate structure, whilst the fine lamellar structure remained unchanged. The mechanism of tensile fracture of the alloy is discussed in relation to the stress-induced phase transformation and microstructural change. An intrinsic co-relationship of phase transformation between the aged and tensile deformed alloy specimens is also discussed.

Exothermic reaction in eutectoid Zn–Al based alloys

Abstract Both solution treated and quench-aged eutectoid Zn–Al based alloys (ZnAl20Cu3Si2 and ZnAl22Cu2 in wt.%) were studied by differential scanning calorimeter (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. An exothermic phenomenon was observed at the early stage of ageing. Similar behavior was also found for the cast eutectoid Zn–Al alloy. The activation energy for the exothermic phenomenon was calculated, which was in a good agreement with that derived from X-ray diffraction examination for the decomposition of the supersaturated β ′ s phase in the eutectoid Zn–Al based alloy. It is concluded that the decomposition of the β ′ s phase is an exothermic solid state reaction in the eutectoid Zn–Al based alloys.

Ultra-precision machining induced surface structural changes of Zn–Al alloy

Abstract Ultra-precision machining was carried out on a furnace cooled (FC) eutectoid Zn–Al alloy specimen using a new technology of single point diamond turning (SPDT). Microstructural changes and phase decomposition at the surface of the ultra-precision machined alloy specimen were investigated. It was found that the ultra-precision machining induced external stress resulted in decomposition of the e phase and crystal orientation changes of the Zn-rich phases: η and e , at the surface of the machined FC Zn–Al alloy specimen, which were in agreement with the tensile stress induced phase transformations and crystal orientation changes in the FC Zn–Al alloy specimen.

Use of EBSD to study electropulsing induced reverse phase transformations in a Zn–Al alloy (ZA22)

Multi‐phase identification and phase transformations in electropulsing treated Zn–Al based alloy wire specimens were studied using electron back‐scattered diffraction, back‐scattered scanning electron microscopy and X‐ray diffraction techniques. By using electron back‐scattered diffraction, two phases: η′S and η′T with a small difference of about 1% in lattice parameters (c0/a0) were identified, based on the determined lattice parameters of the phases, and the reverse eutectoid phase transformations: η′T+ɛ′T+α′T→η′S and ɛ+α→T′+η were successfully detected. Electron back‐scattered diffraction appeared to be an effective technique for studying complex electropulsing induced phase transformations.

Use of EBSD to identify phases in interdendrite region of a cast Zn-Al-based alloy (ZA27).

Electron backscattered Kikuchi diffraction methodology was used to identify phases in the interdendrite region of an alloy ZA27. Two Zn‐rich hexagonal close‐packed structure phases η and ɛ phases were distinguished using predetermined lattice parameters of the phases. In relation to studies of scanning electron microscopy and X‐ray diffraction, electron backscattered diffraction results revealed that the Al‐rich precipitates of the α phase were from decomposition of the η′T, and the four‐phase transformation: α+ɛ→ T′+η, had occurred in the ɛ phase after ageing at 150°C for 8 h.

Microstructure and phase decomposition of quasi-crystal Zn60Mg30Y10 alloy

Abstract The microstructure and aging characteristics of a quasi-crystal Zn 60 Mg 30 Y 10 alloy were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Typical structures of the icosahedral quasi-crystalline phase were characterized by three symmetries: 5-fold, 3-fold and 2-fold, based on which a structure model of this complex quasi-crystalline phase was proposed. Fine-dispersed precipitates were found inside the relatively stable quasi-crystalline phase during aging. Decomposition of the crystalline phase (MgZn 2 ) was also investigated.

Microstructural changes at the ultra-precision machined surface of Zn-Al based alloy

Abstract Using X-ray diffraction and back-scattered electron microscopy techniques, microstructural changes and phase decomposition at the ultra-precision machined surface of a Zn – Al based alloy were studied. The effects of the depth of cut on the microstructural changes were discussed in relation to the creep deformation, and the milling-induced microstructural changes. Structural evolution of the chip from the machining was studied in order to understand the ultra-precision machining induced phase decomposition. The effect of ultra-precision machining on the hardness of the surface of the alloy specimen was studied.