Comparative Study on Wire-Arc Additive Manufacturing and Conventional Casting of Al-Si Alloys: Porosity, Microstructure and Mechanical Property

doi:10.1007/s40195-021-01314-1

Abstract

Abstract:

Here, we compare the porosity, microstructure and mechanical property of 4047 Al-Si alloys prepared by wire-arc additive manufacturing (WAAM) and conventional casting. X-ray microscopy reveals that WAAM causes a higher volume fraction of gas pores in comparison with conventional casting. Effective refinements of α-Al dendrites, eutectic Si particles and Fe-rich intermetallic compounds are achieved by WAAM, resulting from its rapid solidification process. Both ultimate tensile strength (UTS, up to 205.6 MPa) and yield stress (YS, up to 98.0 MPa) are improved by WAAM at the expense of elongation after fracture. The mechanical property anisotropy between scanning direction and build direction is minimal for alloys via WAAM. Additional microstructure refinement and strength enhancement are enabled by increasing the travel speed of welding torch from 300 to 420 mm/min.

Key words: Wire-arc additive manufacturing, Al-Si alloy, Porosity, Microstructure, Strength

Yueling Guo, Qifei Han, Jinlong Hu, Xinghai Yang, Pengcheng Mao, Junsheng Wang, Shaobo Sun, Zhi He, Jiping Lu, Changmeng Liu. Comparative Study on Wire-Arc Additive Manufacturing and Conventional Casting of Al-Si Alloys: Porosity, Microstructure and Mechanical Property[J]. Acta Metallurgica Sinica (English Letters), 2022, 35(3): 475-485.

Figures/Tables 11

Table 1 Chemical composition of SAL4047 welding wire measured using a direct reading spectrometer (wt%)

Element	Al	Si	Fe	Cu	Mn	Mg	Zn	Ti
Nominal range	Bal.	11.0-13.0	< 0.60	< 0.30	< 0.15	< 0.10	< 0.20	< 0.15
Measured	Bal.	11.5	0.543	0.023	0.098	0.085	0.120	0.075

Fig. 1 a Schematic illustration of cold metal transfer (CMT)-based WAAM; b sampling positions for microstructure analysis and mechanical testing along building direction (BD) and scanning direction (SD); c specimen dimensions for tensile testing

Fig. 2 Front a, c and sectional b, d views of conventional WAAM-fabricated 4047 Al-Si alloys with a respective travel speed of 300 mm/min (AM300, a, b) and 420 mm/min (AM420, c, d)

Fig. 3 Optical images of the microstructures within melt pools for WAAM-fabricated 4047 Al-Si alloys with a respective travel speed of 300 mm/min (AM300, a and 420 mm/min (AM420, b), as well as the cast counterpart alloy c. d Secondary dendrite arm spacing (SADS) of each alloy. e XRD spectra of conventional cast alloy as well as AM300 and AM420 alloys

Fig. 4 SEM images showing the microstructures at melt pool boundaries for WAAM-fabricated 4047 Al-Si alloys with a respective travel speed of 300 mm/min (AM300, a1, a2, a3) and 420 mm/min (AM420, b1, b2, b3), as well as the cast counterpart alloy c1, c2, c3. d1 and d2 SEM-EDS mapping of Al and Si within the selected region shown in a1

Fig. 5 Three-dimensional distributions of pores within the WAAM-fabricated 4047 Al-Si alloys with a respective travel speed of 300 mm/min (AM300, a, c) and 420 mm/min (AM420, b, d). The gray-contrast background in a and b is the alloy sample. c, d Pores extracted from a, b, respectively, with colored surfaces

Fig. 6 Relative frequencies of aspect ratio and mean Feret diameter for the WAAM-fabricated 4047 Al-Si alloys with a respective travel speed of 300 mm/min (AM300, a, c) and 420 mm/min (AM420, b, d)

Table 2 Mechanical properties of cast and WAAM-fabricated Al-Si alloys using SAL4047 welding wires with travel speeds of 300 mm/min (AM300) and 420 mm/min (AM420)

Alloys	Yield strength (MPa)	Ultimate tensile strength (MPa)	Elongation after fracture (%)
Cast	88.3 ± 1.6	173.1 ± 2.4	17.8 ± 4.3
AM300-SD	92.3 ± 0.7	196.7 ± 0.8	14.4 ± 0.1
AM300-BD	92.2 ± 3.0	193.4 ± 3.5	11.6 ± 1.5
AM420-SD	98.0 ± 3.1	204.5 ± 5.1	13.2 ± 0.1
AM420-BD	96.6 ± 0.5	205.6 ± 5.8	10.6 ± 1.1

Fig. 7 Fracture surfaces of the WAAM-fabricated 4047 Al-Si alloys with a respective travel speed of 300 mm/min (AM300-SD, a, c) and 420 mm/min (AM420-SD, b, d). a3 and b3 SEM-EDS mapping of the selected region in a2 and b2, respectively, showing the distributions of Al and Si

Fig. 8 Fracture surface of the cast counterpart 4047 Al-Si alloy a-c and the corresponding SEM-EDS mapping of the distributions of Al d, Si e and Fe f, respectively

Fig. 9 Radar chart to compare the porosity, microstructure and mechanical property of 4047 Al-Si alloys via WAAM and conventional casting

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