General Rule of Phase Decomposition in Zn-Al Based Alloys (II)

Abstract

Microstructural changes and phase transformation of Zn-Al based alloys (ZA alloys) were systematically investigated during various thermal and thermo-mechanical processes using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe micro-analysis (EMPA), transmission electron microscopy (TEM), electron back-scattered diffraction (EBSD) and differential scanning calorimeter (DSC) etc. techniques. Phase decompositions of the alloys were studied under various thermal and thermo-mechanical circumstances. General rule of phase decomposition (II) (On effects of external stresses on phase transformation) was summarized with explanations from point view of Gibbs free energy.

Effect of phase transformations on hardness in Zn-Al-Cu Alloys

“…The increase in Cu content was observed to be related to the increase in the intensity of X-ray diffraction peaks corresponding to the θ phase. This phase may be formed by the eutectic reaction L → α + θ located in the Al-Cu rich side 6 . In contrast, the peak intensity of the Zn-rich η phase also increases with the increase in Zn content.…”

“…Nevertheless, the Cu addition, in certain proportions, diminishes certain physical properties such as, ductility 5 . Most of the research works [6][7][8] in the Zn-Al-Cu alloys are related to alloy compositions close to the eutectoid composition, see Figure 1. However, it is also important to know the phase transformations and mechanical properties of Al-rich and Zn-rich Zn-Al-Cu alloys.…”

Dynamic Electropulsing Induced Phase Transformations in a Furnace Cooled Zn-Al Based Alloy (ZA22)

“…[30][31][32][33] The former occurred at the early stage of ageing or in that part of the specimen with less external stress, corresponding to an equilibrium, þ " ¼ þ at 276 C. And the latter occurred at the prolonged stage of ageing or in that part of the specimen with higher external stress, correlating with another equilibrium, " þ ¼ T 0 þ at 268 C. 33) The correlation between the phase transformations in the aged and in the dynamic EPT FC-ZA alloys is schematically shown in Fig. 6, where the reverse phase transformations are indicated by dashed lines.…”

Effects of Dynamic Electropulsing on Phase Transformation of a Zn-Al Based Alloy

“…This reverse phase transformation had never been detected in any thermal, and thermo-mechanical processes in the Zn-Al based alloys. [15][16][17][18][19][20][21][22][23][24] The above mentioned phase transformation and the reverse phase transformation were detected in the XRD examination.…”