Microstructure, Texture Evolution, and Mechanical Properties of ECAP-Processed ZAT522 Magnesium Alloy

doi:10.1007/s40195-019-00969-1

Abstract

Abstract:

In this work, the high-strength Mg-5Zn-2Al-2Sn (ZAT522, in wt%) Mg alloys was obtained at 220 °C and 130 °C by a two-step equal channel angular pressing (ECAP). For each stage, two passes were used. The results showed a remarkable grain refinement after the first stage of ECAP (A2 samples), leading to a fine-grained structure with average size of 1.40 μm. The additional stage (A4 samples) caused further grain refinement to 1.18 μm, and an ultra-fine grain structure (700 nm) appeared in the precipitate-rich region. The grain refinement mechanism for both samples was discussed in detail. To this end, the original extrusion fiber texture evolved into a new strong texture characterized by the base planes tilted toward the ECAP shear plane, with a higher Schmid factor value of 0.34. Compared with the as-extruded alloy, the yield strength of the A2 samples increased from 180 to 245 MPa, which was mainly attributed to the combined effects of grain boundary strengthening and precipitation strengthening. In the case of A4 samples, the dislocation strengthening resulted in a net increase in yield strength to 335 MPa, while the ductility was significantly reduced.

Key words: Mg-5Zn-2Al-2Sn Mg alloy, ECAP, Microstructure, Texture, Tension properties

Ying Ma, Fu-Yin Han, Cheng Liu, Ming-Zhe Li. Microstructure, Texture Evolution, and Mechanical Properties of ECAP-Processed ZAT522 Magnesium Alloy[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(2): 233-242.

Figures/Tables 8

Fig. 1 a Microstructure, b grain size distribution, c SEM micrograph, d (0001) and (10-10) pole figures of A0

Fig. 2 Grain boundary map a, d, SEM micrographs b, e and grain size distributions c, f of the ECAP samples: a-c A2, d-f A4

Fig. 3 SEM micrographs showing a, d, g both precipitate-rich (PR) and precipitate-poor (PP) regions, b, e, h only RP region, and c, f, i only PP region of the as-extruded A0 a-c, the ECAP-processed d-f A2, g-i A4 samples

Table 1 Microstructure characteristics of the ECAP ZAT522 samples

Fig. 4 Different types of grains of the ECAP-processed ZAT522 alloys a A2, b A4: blue-recrystallized, yellow-substructured, red-deformed; c and d frequency of the different types of grains as shown in a, d, respectively

Fig. 5 (0002) pole figures of the ECAP-processed ZAT522 alloys: a A2, b A4

Fig. 6 Distributions of Schmid factors for the (0001) <10-20> base slip of the deformed samples: a A0, b A2, c A4

Fig. 7 Tensile stress-strain curves of the deformed ZAT522 alloys, and corresponding SEM views of the fracture surfaces of A2 and A4 samples

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