High-strength Al–5Mg₂Si–2Mg–2Fe alloy with extremely high Fe content for green industrial application through additive manufacturing

Figures & data

Figure 1. SEM image showing (a) the surface morphologies and (b,c) the cross-sectioned morphologies of pre-alloyed Al–5Mg₂Si–2Mg–2Fe powder; (d) schematic diagram of laser beam scanning procedure; (e) optical micrograph showing the tensile samples and square samples; (f) XRD spectra of the Al–5Mg₂Si–2Mg–2Fe alloy under as-LPBFed and as-aged conditions.

Table 1. The composition of experimental Al–5Mg₂Si–2Mg–2Fe powder calibrated by ICP-AES.

Alloys	Mg	Si	Mn	Fe	Others	Al
Al–5Mg2Si–2Mg–2Fe (wt.%)	5.40	2.64	0.80	2.22	<0.08	Bal.

Figure 2. (a–d) SEM and (e,f) TEM images showing the microstructure of as-LPBFed Al–5Mg₂Si–2Mg–2Fe alloy; (a) the overall microstructure; (b,c) the detailed microstructure in zone L1 and zone L2, respectively; (d) the overall microstructure after deep etching; (e) BF-TEM image showing the detailed microstructure in zone L1; (f) STEM image displaying the detailed microstructure in zone L2.

Figure 3. Details of TEM analysis of microstructure of the as-LPBFed Al–5Mg₂Si–2Mg–2Fe alloy: (a–d) the interface relationships between Al matrix and Mg₂Si as well as white particles; (e, e₁–e₅; f, f₁–f₅) showing the elemental mapping of the cells and MPB zone where particle enriches, respectively.

Table 2. Average compositions (wt.%) of the different regions measured by quantitative TEM/EDX analysis (Figure 4b and Figure S2) in the as-LPBFed Al–5Mg₂Si–2Mg–2Fe alloy.

Alloy	Mg	Si	Mn	Fe	Al
Point of L2 (Figure 4b) wt.%	0.01	5.12	6.33	7.85	80.69
Zone of L1 (Figure S2a) wt.%	3.78	0.24	0.41	0.25	95.32
Zone of L2 (Figure S2a) wt.%	13.82	8.11	2.42	13.52	62.13
EDX mapping (Figure S2a) wt.%	6.01	1.63	0.70	1.83	89.83
Zone of L3(Figure S2b) wt.%	3.40	0.29	0.43	0.22	95.66
EDX mapping (Figure S2b) wt.%	5.65	1.50	0.73	2.04	90.08

Figure 4. SEM/TEM images showing the as-LPBFed Al–5Mg₂Si–2Mg–2Fe alloy with ageing at 180°C for 3.5 h; (a,d,e) the overall microstructure; the detailed microstructure in zone L1 (b) and zone L2 (c); (f) the formation of in-situ Mg₂Si particles with eutectic network; (g) the formation of low number density of α-Al₁₂(Fe,Mn)₃Si particle at the MPC zone.

Figure 5. Detailed TEM analysis of as-LPBFed Al–5Mg₂Si–2Mg–2Fe alloy with ageing at 180°C for 3.5 h; (a,b,L1,L2) the formation of Mg₂Si particles within Mg₂Si eutectics; (c) the formation of high number density α-Al₁₂(Fe,Mn)₃Si particle at the MPB zone; (d, d₁–d₅) EDS maps of Mg₂Si eutectics; (e, e₁–e₅) EDS maps of in-situ Mg₂Si particles; (f, f₁–f₅) EDS maps of α-Al₁₂(Fe,Mn)₃Si particles distributed at MPB zone.

Figure 6. EBSD-inverse pole figures (IPFs) of the as-LPBFed Al-5Mg₂Si-2Mg-2Fe alloy along (a) horizontal and (b) building directions; (c) schematic images showing the direction of samples; (d) corresponding IPF map.

Figure 7. (a) Equilibrium phase diagram of Al–Mg₂Si and Al–5Mg₂Si–2Mg alloy; (b) vertical cross-section of Al–5Mg₂Si–2Mg–xFe alloy; (c) the crack susceptibility index (CSI) calculated via T vs. (f_s)^1/2 curves of Al–5Mg₂Si–2Mg–xFe alloy; (d) Scheil solidification simulation of the Al–5Mg₂Si–2Mg–2.2Fe–0.8Mn alloy.

Figure 8. The effects of high SV on (a) the solidification path (b) the Fe solubility in α-Al considering the α-Al phase as the primary phase.

Table 3. Kinetic parameters for the Al–5Mg₂Si–2Mg–2Fe alloy.

Parameter	Value	Unit	Description	Ref
γ	0.163	J/m^2	Solid/liquid interfacial energy	Zhang et al. 2020
ΔHf	1.36 × 10^9	J/m^3	Heat of fusion	Zhang et al. 2020
g	30	NA	Geometric factor for coarsening	Zhang et al. 2020
v0	1000	m/s	Kinetic pre-factor for ΔTk	Zhang et al. 2020
α0	1	Nm	Solute trapping parameter	Zhang et al. 2020
G	…	K/m	Thermal gradient
SV	…	m/s	Solidification velocity
CR	…	K/s	Cooling rate: CR = G × SV

Figure 9. (a) Tensile stress-strain curves of the Al–5Mg₂Si–2Mg–2Fe alloy without and with ageing treatment; (b,c) tensile fractured morphology; (d) comparison of the tensile properties between the Al–5Mg₂Si–2Mg–2Fe alloy in this study and other Al alloys fabricated by casting, LPBF and HPDC methods.

Figure 10. TEM analysis of the (a,b) as-LPBFed and (c,d) as-aged Al–5Mg₂Si–2Mg–2Fe alloy after tensile testing: (a) the interaction between dislocations and Mg₂Si eutectics at the MPC zone; (c) the interaction between dislocations and Mg₂Si eutectics and in-situ Mg₂Si particles at the MPC zone; (b,d) The interaction between dislocations and α-Al₁₂(Fe,Mn)₃Si particles at the MPB zone.

Figure 11. The contributions of different strengthening mechanisms to the YS.

Figure 12. Schematic image showing the microstructural characteristics in this work.

Zhang, F., C. Zhang, S. M. Liang, D. C. Lv, and W. S. Cao. 2020. “Simulation of the Composition and Cooling Rate Effects on the Solidification Path of Casting Aluminum Alloys.” Journal of Phase Equilibria and Diffusion 41: 793–803. https://doi.org/10.1007/s11669-020-00834-0.

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Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.