Achieving superior mechanical properties of selective laser melted AlSi10Mg via direct aging treatment

doi:10.1016/j.jmst.2021.07.059

Abstract

Abstract:

For additive manufactured aluminum alloys, the inferior mechanical properties along the building direction have been a serious weakness. In this study, an optimized heat treatment was developed as a simple and effective solution. The effects of direct aging on microstructure and mechanical properties along the building direction of AlSi10Mg samples produced via selective laser melting (SLM) were investigated. The results showed that, compared with the conventional heat treatment at elevated temperatures, direct aging at temperatures of 130-190 °C could retain the fine grain microstructure of SLM samples and promote further precipitation of Si phase, however, the growth of pores occurred during direct aging. With increasing aging temperature, while finer cell structures were obtained, more and larger pores were developed, resulting in decreased density of the samples. Two types of pore formation mechanisms were identified. Considering the balance between the refinement of cell structure and the growth of pores, aging at 130 °C was determined as the optimized heat treatment for SLM AlSi10Mg samples. The tensile strength along the building direction of the 130 °C aged sample was increased from 403 MPa to 451 MPa, with relatively high elongation of 6.5%.

Key words: Additive manufacturing, Selective laser melting, AlSi10Mg alloy, Heat treatment

H. Zhang, Y. Wang, J.J. Wang, D.R. Ni, D. Wang, B.L. Xiao, Z.Y. Ma. Achieving superior mechanical properties of selective laser melted AlSi10Mg via direct aging treatment[J]. J. Mater. Sci. Technol., 2022, 108: 226-235.

Figures/Tables 17

Fig. 1. (a) AlSi10Mg powders, (b) internal morphology (the arrows indicate pores inside the powders), and (c) particle size distribution.

Fig. 2. AlSi10Mg samples produced by SLM.

Table 1. Parameters for SLM processing and heat treatment.

Parameters	Value
Laser power	275 W
Scanning speed	1.6 m/s
Layer thickness	30 μm
Average particle size	43 μm
Aging temperature	130/150/170/190 °C (4 h)

Fig. 3. DSC profile of SLM AlSi10Mg sample.

Fig. 4. Microstructure of as-fabricated AlSi10Mg samples on (a, b) horizontal and (c, d) building sections.

Fig. 5. Fine cell structures after aging at (a) 130 °C, (b) 150 °C, (c) 170 °C and (d) 190 °C.

Fig. 6. Defect distribution of (a) as-fabricated and (b, c) aged samples, (d) density of as-fabricated and aged samples (arrows indicate pore defects), (e) number and size distribution of pores.

Fig. 7. Defect morphologies of (a, b) as-fabricated and (c) 190 °C aged samples.

Fig. 8. Microstructure of (a) as-fabricated sample and (b) 130 °C aged sample, grain size distribution profiles of (c) 130 °C aged sample and (d) 190 °C aged sample.

Fig. 9. TEM images showing precipitates in (a) as-fabricated sample, (b) 130 °C aged sample, and (c) 190 °C aged sample.

Fig. 10. (a) STEM images of precipitates inside the cells and (b, c) HAADF images of rod-like Si and Mg2Si of 190 °C aged sample.

Fig. 11. (a) Hardness distribution profiles and (b) tensile curves of as-fabricated and aged samples.

Table 2. UTS and EL of as-fabricated and aged samples along building direction.

Processing	YS, MPa	UTS, MPa	EL,%
As fabricated	276 ± 6	403 ± 6	6.37 ± 0.23
130 °C aged 150 °C aged 170 °C aged 190 °C aged	309 ± 1	451 ± 10	6.46 ± 0.43
	296 ± 4	433 ± 13	5.30 ± 1.82
	293 ± 11	408 ± 9	3.18 ± 0.38
	270 ± 14	380 ± 34	3.54 ± 1.71

Fig. 12. Fracture morphologies of (a, b) as-fabricated samples and (c, d) aged samples, the arrows indicate pores observed on the fracture surface.

Fig. 13. KAM maps of as-fabricated sample.

Fig. 14. Illustration of microstructural evolution during SLM and subsequent aging.

Fig. 15. Crack propagation path of (a) as-fabricated and (b) 130 °C aged samples, (c) hardness near molten pool boundaries (the arrows indicate crack propagation through the molten pools).

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