Microstructure and Mechanical Properties of TiB-Containing Al-Zn Binary Alloys

doi:10.1016/j.jmst.2016.04.016

Abstract

Abstract: The microstructure and mechanical properties of newly developed Al-35Zn cast alloys with TiB refiner addition were evaluated by X-ray diffractometry, optical microscopy, and scanning electron microscopy coupled with energy dispersive spectrometry. The microstructure of these alloys featured α-Al dendrites surrounded by Al-Zn (α?+?η) eutectic structures. After the addition of TiB refiner, the alloy grain sizes decreased, and its morphology abruptly changed from dendritic to equiaxed grains. Such an improved microstructure of the modified alloys was accompanied by a significant increase in the tensile strength and elongation percentage compared to those of the Al-Zn or Zn-Al-based alloys. The results showed that with the increase of TiB content up to 0.05%, the morphology of α-Al dendrites and α?+?η phases changed from coarse dendrite and lamellar structures into independent and fine ones. Based on these results, the effect of TiB refiner addition on the microstructure and mechanical properties of the Al-35Zn binary alloys was investigated.

Key words: Al-Zn(-Cu) alloy, Eutectic structure, High strength, TiB2

Sang-Soo Shin, Gil-Yong Yeom, Tae-Yang Kwak, Ik-Min Park. Microstructure and Mechanical Properties of TiB-Containing Al-Zn Binary Alloys[J]. J. Mater. Sci. Technol., 2016, 32(7): 653-659.

Figures/Tables 9

XRD patterns of the Al-35Zn binary alloys with 0-0.1% TiB refiner content.

Optical microscopy images for the gravity-cast Al-35Zn alloys with (a) 0.0, (b) 0.01, (c) 0.05, and (d) 0.1% of TiB refiner contents (in 3% HF solution). An EBSD orientation map (inverse pole figure map) shows the grain distribution for the Al-35Zn alloys with (e) 0.0, (f) 0.01, (g) 0.05 and (h) 0.1% TiB refiner contents.

SEM images for the Al-35Zn cast alloys with (a) 0.0, (b) 0.01, (c) 0.05, and (d) 0.1% TiB refiner contents. Arrows point to the 100% Zn phase (in 3% HF solution).

SEM and EDS results for the Al-35Zn cast alloys with (a) 0.0, (b) 0.01, (c) 0.05, and (d) 0.1 wt% TiB refiner contents.

SEM images of the α?+?η lamellar structure in the (a) Al-35Zn gravity cast alloy with 0.01 wt% TiB refiner contents, (b) Al-35Zn gravity cast alloy with 0.05% TiB refiner content, and (c) Al-35Zn gravity cast alloy with 0.1% TiB refiner content.

S-S curves for the Al-35Zn gravity cast alloy as function of TiB refiner content.

(a) Low-magnification optical images of the side surfaces for the deformed Al-35Zn-0.05 wt% TiB alloy sample showing the presence of abundant shear bands (the Al-35Zn 0.05% TiB content alloy is characterized with a large value of elongation to failure). (b) SEM image of the fracture surface after the tensile tests conducted on the Al-35Zn-0.05% TiB content sample.

Secondary electron micrographs recorded for the fracture surface of the Al-35Zn alloy with 0.05% TiB refiner content showing the presence of multiple dimples with sizes less than 25?µm.

Ultimate tensile strengths (MPa) vs. elongation (%) of various Al-Zn or Zn-Al based alloys. 1 Zn-4Al-1Cu[33], 2 ZA8[34], 3 Zn-40Al-2Cu-2.5Si[35], 4 Zn-40Al-2Cu-1Si[36], 5 Zn-27Al-2Cu-1Si[36], 6 Zn-27Al-2Cu[36], 7 Zn-40Al-4Cu[37], 8 Zn-40Al-2Cu-2Si[36], 9 ZA27[38], 10 Zn-40Al-3Cu[37], 11 ZA12[34], 12 Zn-40Al-2Cu[37], 13 Zn-40Al-1Cu[37], 14 ZA27+Zircon[39], 15 ZnAl4Y-0.5TiB[40], 16 Al-Zn-Mg-Ce[41], 17 Al-40Zn-5Cu[12], 18 Al-40Zn-3Cu-3Ni[42], 19 Al-40Zn-3Cu-2Ni[42], 20 Al-40Zn-3Cu-1Ni[42], 21 Al-40Zn-4Cu[12], 22 Al-40Zn-3Cu[12], 23 Al-40Zn-2Cu[12], 24 Al-40Zn-1Cu[12], 25 Al-40Zn[12], 26 Al-35Zn-based alloy, 27 Al-35Zn-0.01% TiB alloy, 28 Al-35Zn-0.05% TiB alloy, 29 Al-35Zn-0.1% TiB alloy.

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