外文翻譯--鋅鋁合金受擠壓后相位分解的彌散分布（英文）

1、JOURNAL OF MATERIALS SCIENCE 34 (1999) 3653– 3658Phase decomposition in extruded Zn-Al based alloyY. H. ZHU?, R. M. HERNANDEZ, L. BA ? NOS Instituto de Investigaciones en Materiales, UNAM, Mexico D.F. 04510, Apartado Pos

2、tal 70-360, Mexico E-mail: mfyhzhu@inet.polyu.edu.hkAgeing characteristics of an extruded eutectoid Zn-Al based alloy were investigated using X-ray diffraction and scanning electron microscopy techniques. The extruded al

3、loy consisted of Al rich α phase and Zn rich η? E and ε phases. The original cast eutectoid Zn-Al alloy was extruded at 250 ?C. Both supersaturated α? s and β? s phase decomposed during extrusion and appeared as fi ne an

4、d coarse lamellar structures. The η? E and ε phases particles formed in the original interdendritic region. It was found that two Zn rich phases η? E and ε decomposed sequentially during ageing at 170, 140 ?C. The decomp

5、osition of the η? E phase occurred as a discontinuous precipitation in the early stage of ageing and the decomposition of the ε phase took place in a four phase transformation: α + ε →T ? + η in the prolonged ageing. Two

6、 typical morphologies of the decomposition of the Zn rich phases η? E and ε were distinctive in back-scattered scanning electron microscopy.C ? 1999 Kluwer Academic Publishers1. Introduction Alloy materials suffer always

7、 various external stresses during their manufacturing and service application. The investigation of the stress induced phase transformation and microstructural change in most alloy materials is of practical importance. D

8、ecomposition of Zn-rich metastable phases in an extruded eutectoid Zn-Al based alloy become recently an interesting topic because of its correlation with di- mensional stability of the material [1–3]. When the eu- tectoi

9、d Zn-Al based alloy (Zn76Al22Cu2 in wt %) was extruded at 210–290 ?C, the Zn-rich phase η? E formed as a metastable phase, and decomposed during isother- mal holding. It was observed that the decomposition of the metasta

10、ble η? E phase resulted in dimensional shrink- age of the material. Another Zn-rich metastable phase ε decomposed during prolonged aging, which caused expansion of the material. In this paper the decomposition of both th

11、e metastable phases η? E and ε in the extruded alloy was in detail investigated during isothermal holding.2. Experimental The eutectoid Zn-Al based alloy material Zn76Al22Cu2 (wt %) was continuously cast into rod of 178

12、mm in diameter, then extruded into rod of 20 mm in diameter after heating up to 250 ?C. The extruded alloy specimens had been previously aged for a period in excess of 2 years at ambient temperature.? Corresponding autho

13、r. Department of Manufacturing Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong, People’s Republic of China.The isothermal holding was carried out at 170 and 140 ?C respectively. X-ray diffraction (X

14、RD) identifi- cation, scanning electron microscopy (SEM) and elec- tron probe micro-analysis (EPMA) techniques were ap- plied for investigation of decomposition of the phases involved and microstructural change during ag

15、eing at 170 and 140 ?C. A X-ray diffractometer with nickel filtered CuKα radiation was employed scanning on flat specimens at a speed of 1 deg/min within a 2θ range from 35? to 47? to obtain characteristic X-ray diffract

16、ion peaks. Standard metallographic examina- tion was carried out in a scanning microscope using back-scattered SEM image to receive visible atomic number contrast.3. Results and discussion 3.1. Decomposition of Zn-rich η

17、? E and ε phases It was observed that the extruded alloy consisted of Al- rich α phase and Zn-rich η? E and ε phases before isother- mal holding, as shown in the X-ray diffractograms of the extruded eutectoid Zn-Al based

18、 alloy at vari- ous stages of ageing at 170 and 140 ?C respectively (Figs 1 and 2). Both supersaturated Al-rich α? s and Zn- rich β? s phase decomposed during extrustion at 250 ?C and appeared as fine and coarse lamellar

19、 structures, as shown in the back-scattered SEM images (Fig. 3). The η? E and ε phases particles formed in the interdendritic region of the original cast eutectoid Zn-Al based alloy.0022–2461 C ? 1999 Kluwer Academic Pub

20、lishers 3653Figure 3 The relative X-ray diffraction (XRD) intensity changes of ε and T ? phases during ageing at 170 ?C (a) and 140 ?C (b).? from (10¯ 10) planes of the ε phase; ? from (433) planes of the T ? phase.

21、(a)Figure 4 Scanning electron micrograph of the extruded eutectoid Zn-Al alloy (a) before ageing, and after ageing at 170 ?C for 1 h (b), 10 h (c), and 50 h (d). → Precipitation of the η? E phase; *→ precipitation of the

22、 ε phase. (Continued)shifted to the lower 2θ, accordingly the d-spacing of the (0002) crystal planes increased, as labeled in Fig. 2. Also the relative changes of the X-ray diffraction in- tensity of ε and T ? phases dur

23、ing prolonged ageing at 140 ?C were observed, as shown in both Figs 2 and 4b. However the phase transformation rate at 140 ?C was apparently lower than that at 170 ?C. As shown in Figs 1 and 2, the X-ray diffraction peak

24、s of the ε phase vanished after 113 h ageing at 170 ?C, whist the (10¯ 10) X-ray diffraciton peak of the ε phase still exsisted after 304 h ageing at 140 ?C.3.2. Microstructural characteristics Theabovementionedtwos

25、tagesofdecompositionwere clearly observed on scanning electron microscope. As shown in the back-scattered SEM images of the ex- truded eutectoid Zn-Al based alloy at various stages of ageing at 170 ?C (Fig. 3), the micro

26、structural evolution of the extruded eutectoid Zn-Al based alloy was char- acteristic of two kinds of decomposition of the Zn-rich η? E and ε phases. Before ageing the microstructure of the extruded eu- tectoid Zn-Al bas