Microstructure and mechanical properties of Al-12Si and Al-3.5Cu-1.5Mg-1Si bimetal fabricated by selective laser melting

doi:10.1016/j.jmst.2019.03.047

Abstract

Abstract:

An Al-12Si/Al-3.5Cu-1.5Mg-1Si bimetal with a good interface was successfully produced by selective laser melting (SLM). The SLM bimetal exhibits four successive zones along the building direction: an Al-12Si zone, an interfacial zone, a texture-strengthening zone and an Al-Cu-Mg-Si zone. The interfacial zone (< 0.2 mm thick) displays an increasing size of the cells composed of eutectic Al-Si and a discontinuous cellular microstructure, resulting in the lowest hardness of the four zones. The texture-strengthening zone (around 0.3 mm thick) shows a remarkable variation of the hardness and <001> fiber texture. Electron backscatter diffraction analysis shows that the grains grow gradually from the interfacial zone to the Al-Cu-Mg-Si zone along the building direction. Additionally, a strong <001> fiber texture develops at the Al-Cu-Mg-Si side of the interfacial zone and disappears gradually along the building direction. The bimetal exhibits a room temperature yield strength of 267 ± 10 MPa and an ultimate tensile strength of 369 ± 15 MPa with elongation of 2.6% ± 0.1%, revealing the potential of selective laser melting in manufacturing dissimilar materials.

Key words: Selective laser melting, Aluminum alloys, Bimetals, Microstructure, Mechanical properties

P. Wang, C.S. Lao, Z.W. Chen, Y.K. Liu, H. Wang, H. Wendrock, J. Eckert, S. Scudino. Microstructure and mechanical properties of Al-12Si and Al-3.5Cu-1.5Mg-1Si bimetal fabricated by selective laser melting[J]. J. Mater. Sci. Technol., 2020, 36: 18-26.

Figures/Tables 8

Fig. 1. Microstructures of the SLM Al-12Si/Al-Cu-Mg-Si bimetal: (a) overview of the bimetal with etching at low magnification (OM); (b) SEM micrograph of the Al-12Si part (inset: cellular microstructure at high magnification); (c) the interface of the base alloys (SEM); (d) Al-Cu-Mg-Si part (SEM). The positions of (b-d) are marked by ellipses in (a).

Fig. 2. (a) EBSD inverse pole figure (IPF) map across the interface along the building direction. The spatial orientation with respect to the building direction (BD), scanning direction (SD) and transverse direction (TD), and the coloring of the orientation component along the biulding direction in the maps are given in the inset; (b) average grain size and relative content of <001> fiber texture as a function of the disctance from the interface.

Fig. 3. Microhardness distribution and EDS line-scan profiles as a function of the distance from the interface (Ref-1: the SLM Al-12Si alloy using the laser power input of 190 W, scanning speed of 165 mm/s, hatch spacing of 0.08 mm and layer thickness of 0.04 mm; Ref-2: the SLM Al-12Si alloy using the power input of 320 W, scanning speed of 1455 mm/s, hatch spacing of 0.11 mm and layer thickness of 0.05 mm; Ref-3: the SLM Al-Cu-Mg-Si alloy using the laser power input of 190 W, scanning speed of 165 mm/s, hatch spacing of 0.08 mm and layer thickness of 0.04 mm).

Fig. 4. Contour maps of the nano-hardness of zones I, II, III and IV.

Fig. 5. (a) SEM images of the bimetal prepared by FIB, and STEM images of the FIB-prepared specimens at 0 mm distance from the interface (left inset) and 0.1 mm distance from the interface (right inset); (b) [001] HAADF-STEM images and corresponding EDS map of the position A at 0 mm distance from the interface; (c) [001] HAADF-STEM image at high magnification and corresponding high-resolution images (bottom-left inset) of the position B at 0.1 mm distance from the interface.

Fig. 6. (a) Tensile true stress-true strain curves of the Al-12Si/Al-Cu-Mg-Si bimetal, the SLM Al-12Si alloy (Ref-2) and the SLM Al-Cu-Mg-Si alloy (Ref-3); (b) A summary of tensile strength (i.e., YS and UTS) versus elongation including our work and conventional bimetals (see Ref. [7]).

Table 1 Comparison of the tensile properties of the SLM Al-12Si/Al-Cu-Mg-Si bimetal, the SLM Al-12Si alloy (Ref-2) and the SLM Al-Cu-Mg-Si alloy (Ref-3).

Materials type	YS (MPa)	UTS (MPa)	Elongation (%)
Al-12Si/Al-Cu-Mg-Si bimetal	267 ± 10	369 ± 15	2.6 ± 0.1
Ref-2	208 ± 8	403 ± 4	5.6 ± 0.3
Ref-3	223 ± 2	372 ± 7	5.8 ± 0.5

Fig. 7. Fracture morphology of the SLM Al-12Si/Al-Cu-Mg-Si bimetal: (a) overview of the fracture site along the building direction (OM), (b) SEM micrograph of the fracture morphology.

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