MECHANICAL PROPERTIES AND WORK HARDENING BEHAVIOR OF COLUMNAR-GRAINED HAl77-2 BRASS
MO Yongda1, JIANG Yanbin1,2, LIU Xinhua1,2, XIE Jianxin1,2()
1 Key Laboratory for Advanced Materials Processing of Ministry of Education, University of Science and Technology Beijing, Beijing 100083 2 Beijing Laboratory of Metallic Materials and Processing for Modern Transportation, University of Science and Technology Beijing, Beijing 100083
Cite this article:
MO Yongda, JIANG Yanbin, LIU Xinhua, XIE Jianxin. MECHANICAL PROPERTIES AND WORK HARDENING BEHAVIOR OF COLUMNAR-GRAINED HAl77-2 BRASS. Acta Metall Sin, 2014, 50(11): 1367-1376.
The mechanical properties and work hardening behavior of columnar-grained HAl77-2 brass were investigated by means of room temperature tensile test, EBSD and TEM. The effects of grain size on the work hardening rate and tensile ductility of the alloy were discussed. Some references reported that deformation twinning developed in the equiaxed-grained brass led to a reduction in slip length of dislocation and an increase in the work hardening rate at the second stage in the curve of work-hardening vs strain. In this work, however, the results showed that the low-angle subgrain boundaries distributed parallelly were formed in the columnar grain and reduced the slip length of dislocation at the second stage, which was responsible for the rise of the work hardening rate. With increasing grain size, both the yield strength and ultimate tensile strength of the columnar-grained HAl77-2 brass decreased, but its elongation to failure increased significantly from 70.4% for the grain size of 2.0 mm to 84.4% for the grain size of 6.0 mm. Higher performance to resist the plastic instability and better deformation uniformity mainly contributed to the ductility improvement of the larger-grain-sized columnar-grained HAl77-2 brass.
Fig.1 Schematic of directional solidification apparatus
Fig.2 Transverse (top) and longitudinal (bottom) macrostructures of the columnar-grained ingots cast under mold heating temperatures of 1273 K (a), 1303 K (b) and 1333 K (c) (SD—solidification direction)
Fig.3 Engineering stress-strain curves of the columnar-grained HAl77-2 brass specimens with different grain sizes
Grain size / mm
ss / MPa
sb / MPa
d / %
2.0
55
218
70.4
3.2
48
199
75.1
6.0
45
182
84.4
Table 1 Mechanical properties of the columnar-grained HAl77-2 brass specimens with different grain sizes
Fig.4 Curves of work hardening rate vs true strain for specimens with different grain sizes
Fig.5 Orientation-imaging-microscopic (OIM) maps (left) and corresponding inverse pole figures (IPFs) (right) of specimens with grain size of 2.0 mm suffered tensile strains (eE) of 0.20 (a) and 0.50 (b) (TD—tensile direction, the rectangle in Fig.5b shows that high angle grain boundaries formed in the columnar grain)
Fig.6 TEM images and corresponding SAED patterns (inset) of specimens with grain size of 2.0 mm suffered eE of 0.20 (a) and 0.50 (b)
Fig.7 OIM maps (left) and corresponding IPFs (right) of specimens with grain size of 6.0 mm suffered eE of 0.20 (a) and 0.50 (b)
Fig.8 Misorientation profiles along the white lines in Figs.5 and 7, showing the intragranular misorientations variation of specimens with different grain sizes deformed to different strains
Fig.9 Longitudinal microstructures near the tensile fractures of specimens with grain size of 2.0 mm (a) and 6.0 mm (b) (GB—grain boundary, the rectangles in Figs.9a and b show cellular substructures )
Fig.10 OM image of the longitudinal section near the tensile fracture of the specimen with grain size of 2.0 mm (a), corresponding (rectangle in Fig.10a) OIM map (b) and Kikuchi pattern quality (KPQ) map (c)
Fig.11 OM image of the longitudinal section near the tensile fracture of the specimen with grain size of 6.0 mm (a), corresponding (rectangle in Fig.11a) OIM map (b) and KPQ map (c) (The rectangle in Fig.11c shows that strain marking crossed low angle grain boundary)
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