Fatigue Improvement of AlSi10Mg Fabricated by Laser-Based Powder Bed Fusion through Heat Treatment
Abstract
:1. Introduction
2. Materials and Methods
2.1. PBF-LB/M Fabrication and Material
2.2. Specimen Specification and Finishing
2.3. Heat Treatment
2.4. Characterization and Testing
3. Results and Discussion
3.1. Heat Treatment
3.2. Tensile
3.3. Fatigue
3.4. Fractography
4. Conclusions
- The microstructure of the NHT material is mainly composed of columnar grains oriented with their <001> crystal direction parallel to the build direction, which is due to the existence of a high thermal gradient within the hatch overlaps.
- SEM results for the NHT condition indicated a weight fraction of primary α-Al higher than the equilibrium content. This is caused by the rapid solidification conditions. Additionally, the nonequilibrium nature of the process suppresses the growth of secondary dendritic arms in α-Al.
- A relatively high hardness of 115 HV was measured for the NHT condition. It is due to the presence of exceptionally fine grains and a high concentration of supersaturated alloying elements within the aluminum matrix. Another contributing factor to the high hardness is the presence of fine Si particles at the grain and subgrain boundaries. It is also worth mentioning that as hardness is associated with plastic deformation, the good work hardening characteristic of the NHT material, as shown in the tensile test results, must have contributed to its high hardness.
- Solution heat-treatment at 500 °C for two hours followed by quenching and then artificial aging at 160 °C for 24 h was selected after performing a series of parametric studies to bring the alloy to its peak-hardened condition. After the heat treatment, columnar dendritic subgrains, as well as hatch overlaps, disappear through compositional homogenization, which implies the elimination of the anisotropic microstructural and mechanical properties of the NHT material. At peak-hardened condition, the hardness of 116 HV was measured, which is primarily caused by precipitation hardening of the alloy with nanoscale β-Mg2Si precipitates.
- The flow curves indicate a simultaneous improvement of both yield strength and tensile elongation in HT condition. This can be explained very well by the following effects: Firstly, the residual stress accumulated in the specimen during the PBF-LB/M process is recovered after the heat treatment, thus reducing the probability of fracture in regions of the NHT specimen under high local stresses. Secondly, the impact of the Hall–Petch strengthening factor is preserved after heat treatment, as the grain size after SHT remains similar to that observed in NHT condition. Lastly, Mg2Si precipitation further contributes to strengthening.
- Although there is a slight decrease in the ultimate tensile strength, fatigue life after heat treatment is improved because of an increase in the yield strength. Moreover, in both NHT and HT specimens, fatigue failure is initiated from large defects located just below or on the specimen surface for all stress levels. The heat treatment did not have much influence on the size of initiating defects, which were typically of the order of 100 to 150 µm.
- The fracture mechanism after heat treatment changes from quasi-brittle to a more ductile type. Fracture surface examinations indicated that the quasi-cleavage pattern of the alloy in the NHT condition converts into relatively larger dimples in the crack propagation zone in the HT condition.
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Laser Power (W) | Scanning Speed (mm/s) | Beam Diameter (mm) | Hatch Space (mm) | Slice Thickness (mm) | Scanning Strategy |
---|---|---|---|---|---|
420 | 1300 | 0.1 | 0.21 | 0.06 | Chess pattern |
Si | Mg | Fe | Cu | Mn | Ni | Zn | Pb | Sn | Ti | Al |
---|---|---|---|---|---|---|---|---|---|---|
9–11 | 0.2–0.45 | 0.55 | 0.05 | 0.45 | 0.05 | 0.1 | 0.05 | 0.05 | 0.15 | balance |
Parameters/Stages | Solution Heat-Treatment | Artificial Aging |
---|---|---|
Time in hours | 0:10, 0:20, 0:30, 1:00, 2:00 | 1:00, 2:00, 4:00, 8:00, 12:00, 24:00, 48:00 |
Temperature in °C | 300, 400, 500 | 140, 160, 180 |
Conditions/Properties | σY (Rp0.2) in MPa | σUTS in MPa | εfracture in % |
---|---|---|---|
NHT | 187 ± 3 | 347 ± 5 | 4.5 ± 0.3 |
HT | 240 ± 3 | 305 ± 3 | 6.0 ± 0.3 |
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Sajadi, F.; Tiemann, J.-M.; Bandari, N.; Cheloee Darabi, A.; Mola, J.; Schmauder, S. Fatigue Improvement of AlSi10Mg Fabricated by Laser-Based Powder Bed Fusion through Heat Treatment. Metals 2021, 11, 683. https://doi.org/10.3390/met11050683
Sajadi F, Tiemann J-M, Bandari N, Cheloee Darabi A, Mola J, Schmauder S. Fatigue Improvement of AlSi10Mg Fabricated by Laser-Based Powder Bed Fusion through Heat Treatment. Metals. 2021; 11(5):683. https://doi.org/10.3390/met11050683
Chicago/Turabian StyleSajadi, Felix, Jan-Marc Tiemann, Nooshin Bandari, Ali Cheloee Darabi, Javad Mola, and Siegfried Schmauder. 2021. "Fatigue Improvement of AlSi10Mg Fabricated by Laser-Based Powder Bed Fusion through Heat Treatment" Metals 11, no. 5: 683. https://doi.org/10.3390/met11050683