Microstructure evolution and mechanical properties at high temperature of selective laser melted AlSi10Mg

doi:10.1016/j.jmst.2020.04.066

Abstract

Abstract:

In this study, the microstructure and tensile properties of selective laser melted AlSi10Mg at elevated temperature were investigated with focus on the interfacial region. In-situ SEM and in-situ EBSD analysis were proposed to characterize the microstructural evolution with temperature. The as-fabricated AlSi10Mg sample presents high tensile strength with the ultimate tensile strength (UTS) of ～450 MPa and yield strength (YS) of ～300 MPa, which results from the mixed strengthening mechanism among grain boundary, solid solution, dislocation and Orowan looping mechanism. When holding at the temperature below 200 °C for 30 min, the microstructure presents little change, and only a slight decrement of yield strength appears due to the relief of the residual stress. However, when the holding temperature further increases to 300 °C and 400 °C, the coarsening and precipitation of Si particles in α-Al matrix occur obviously, which leads to an obvious decrease of solid solution strength. At the same time, matrix softening and the weakness of dislocation strengthening also play important roles. When the holding temperature reaches to 400 °C, the yield strength decreases significantly to about 25 MPa which is very similar to the as-cast Al alloy. This might be concluded that the YS is dominated by the matrix materials. Because the softening mechanism counteracts work hardening, the extremely high elongation occurs.

Key words: Selective laser melting, AlSi10Mg, Microstructure, In-situ EBSD, High temperature tensile property

Y. Cao, X. Lin, Q.Z. Wang, S.Q. Shi, L. Ma, N. Kang, W.D. Huang. Microstructure evolution and mechanical properties at high temperature of selective laser melted AlSi10Mg[J]. J. Mater. Sci. Technol., 2021, 62: 162-172.

Figures/Tables 17

Table 1 Chemical composition of investigated AlSi10Mg alloy powder (wt%).

Al	Si	Mg	Fe	Mn	Zn	Ti	Cu	O
Balance	9.34	0.34	0.38	0.15	0.052	0.036	<0.03	0.046

Fig. 1. Micrograph of AlSi10Mg powder used in this study.

Table 2 SLM processing parameters.

Laser power	Scanning speed	Hatching distance	Beam radius	Layer thickness
340 W	1600 mm/s	100 μm	70 μm	30 μm

Fig. 2. Schematic illustration of SLM scanning process and specimens for (a) SEM and EBSD microstructural analyses and (b) tensile test.

Fig. 3. Microstructures of as-built AlSi10Mg samples: (a) inner and boundary of molten pool and high magnification images of (b) inner and (c) boundary regions.

Fig. 4. Microstructure of as-built and exposed SLM AlSi10Mg specimens: (a), (b), (c), (g), (h) and (i) as-built samples; (d) and (j) at 100 °C for 30 min; (e) and (k) at 200 °C for 30 min; (f) and (l) at 300 °C for 30 min (AB: as built and HT: heat treated).

Fig. 5. Microstructures of as-built and exposed SLM AlSi10Mg specimens: (a) and (b) represent as-built sample; (c) and (d) at 400 °C for 15 min; (e) and (f) at 400 °C for 30 min (AB: as built and HT: heat treated).

Fig. 6. Schematic illustration of microstructure evolution of the SLMed AlSi10Mg samples: (a) asbuilt conditions, (b) after exposure at 100 °C and 200 °C for 30 min, (c) after exposure at 300 °C for 30 min, (d) after exposure at 400 °C for 15 min, (e) after exposure at 400 °C for 30 min.

Fig. 7. Orientation color maps: (a) and (b) before and after exposure at 200 °C for 30 min, respectively; (c) and (d) before and after exposure at 400 °C for 30 min, respectively; Pole figures of AlSi10Mg alloy samples: (e) and (f) before and after exposure at 200 °C for 30 min, respectively; (h) and (i) before and after exposure at 400 °C for 30 min, respectively.

Fig. 8. KAM maps of AlSi10Mg samples: (a) and (b) before and after exposure at 200 °C for 30 min, respectively; (c) and (d) before and after exposure at 400 °C for 30 min.

Fig. 9. Tensile curves of as-built AlSi10Mg alloy: (a) true stress-strain curves and (b) engineering stress-strain curves.

Fig. 10. Variation of tensile properties with temperature of as-built AlSi10Mg alloy [16,22,27]: (a) YS and UTS and (b) elongation (SR: stress relief heat treated).

Table 3 Mechanical properties of SLMed AlSi10Mg specimens at as-built and heated conditions.

Test temperature (°C)	YS (MPa)	UTS (MPa)	Elastic modulus (GPa)	Elongation (%)
25	322 ± 10	460 ± 7	76 ± 4	6.94 ± 0.85
100	298 ± 7	382 ± 12	65 ± 2	13.14 ± 3.05
200	236 ± 8	266 ± 19	59 ± 1	23.73 ± 0.38
300	143 ± 6	150 ± 9	49 ± 3	26.56 ± 3.10
400	25 ± 3	30 ± 4	18 ± 2	75.02 ± 4.02

Table 4 Solid solubility of Si in Al matrix and contribution of solution strengthening.

Sample	Solid solubility [36] (wt%)	σ_SSS (MPa)	Δσ_SSS (MPa)
As-fabricated	7.89	86.8	0
300 °C	3.02	33.2	-53.6
500 °C	1.67	18.4	-68.4

Table 5 Mean diameter and fraction of nano-Si and contribution of Orowan looping mechanism.

Sample	Mean diameter (nm)	Fraction (%)	Shear modulus (GPa)	σ_orowan (MPa)	Δσ_orowan (MPa)
As-fabricated	46	0.08	28.2	106.9	0
300 °C	51	0.26	18.2	112.1	5.2
400 °C	83	0.46	6.3	31.7	-75.2

Fig. 11. Fracture surfaces of AlSi10Mg tensile specimens: (a), (b) and (c) the graphs of testing temperature at RT, 100 °C, 200 °C, respectively; (d), (e) and (f) the amplification graphs of (a), (b) and (c), respectively.c.

Fig. 12. Fracture surfaces of AlSi10Mg tensile specimens: (a) and (c) the graphs of testing temperature at 300 °C; (b) and (d) the graphs of testing temperature at 400 °C.

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