Effect of Semisolid and Heat Treatment Process on Microstructural Refinement of Al–7Si Alloy
Abstract
:1. Introduction
2. Materials and Methods
3. Results
3.1. Microstructure of as-cast Al–Si Alloy
3.2. Microstructure after Cooling Slope Process
3.3. Microstructure after Thixoforming Process
3.4. Microstructure after the Heat Treatment
3.5. Effect of the Heat Treatment on the Intermetallic Compounds
3.6. Effect of Refinement Microstructure on the Hardness
3.7. Effect of Refinement Microstructure on the Corrosion
3.7.1. Immersion Test Results Analysis
3.7.2. Electrochemical Test Results Analysis
4. Conclusions
- The primary dendritic α-Al phase morphology in the Al–7Si alloy as-cast sample was transformed into a fine globular shape in the cooling slope process using a cooling slope. However, in the thixoformed sample, due to heating, the primary α-Al phase morphed into a roughly spherical shape that was equally distributed and surrounded by the eutectic phase.
- The coarse flake-shaped Si particles in as-cast sample were changed into lamellar-like shaped particles, measuring 3.2 ± 0.57 μm after cooling slope. The highest pressure imposed on the thixoformed sample increased the cooling rate, transforming the Si particles into fine acicular-shaped particles, measuring 2.51 ± 0.75 μm.
- During the T6 heat treatment process of the Al–7Si alloy, the eutectic flaky-, lamellar- and acicular-like shaped eutectic Si particles were fragmented and spheroidized via a coarsening and spheroidization process measuring 2.32 ± 0.34 and 1.92 ± 0.87 μm, respectively.
- The increase in hardness of the Al–7%Si alloy after cooling slope and thixoformed processing is due to the microstructural transformation from coarse dendrite to globular α-Al, altering Si particle size and morphology as well as structural homogeneity. The alloy hardness increased from 65 HV to 99 HV and 104 HV after the cooling slope and thixoformed process, respectively.
- The presence of a relatively large eutectic phase promotes wider corrosion on the surface of the as-cast sample than the thixoformed and cooling slope samples. Different from the as-cast sample, the cooling slope and thixoformed samples have a smaller area of localized corrosion. The substantially refined Si particles and reduced eutectic phase area may be ascribed to the lower corrosion rate and improved polarisation resistance of as-cast, cooling slope and thixoformed samples following T6 heat treatment processing. This finding could be due to the smaller cathodic to anodic area ratio.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Samples | Si Size (µm) |
---|---|
As-cast | 4.56 ± 1.18 |
As-cast—T6 | 2.76 ± 0.68 |
Cooling slope | 3.2 ± 0.57 |
Cooling slope—T6 | 2.32 ± 0.34 |
Thixoformed | 2.51 ± 0.76 |
Thixoformed—T6 | 1.92 ± 0.87 |
Samples | Microhardness (HV) |
---|---|
As-cast | 65 |
As-cast—T6 | 79 |
Cooling slope | 86 |
Cooling slope—T6 | 99 |
Thixoformed | 90 |
Thixoformed—T6 | 104 |
Samples | Ecorr. (V) | icorr. (A/cm2) | Rp (Ω·cm2) | CR (mm·y−1) |
---|---|---|---|---|
As-cast | −0.698 | 3.894 × 10−6 | 5.212 × 103 | 0.04240 |
As-cast—T6 | −0.710 | 8.432 × 10−7 | 2.035 × 104 | 0.01600 |
Cooling slope | −0.769 | 1.790 × 10−6 | 9.690 × 103 | 0.01950 |
Cooling slope—T6 | −0.702 | 7.258 × 10−7 | 2.180 × 104 | 0.00790 |
Thixoformed | −0.697 | 1.770 × 10−6 | 2.522 × 104 | 0.0193 |
Thixoformed—T6 | −0.742 | 6.587 × 10−7 | 3.779 × 104 | 0.00740 |
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Gebril, M.A.; Omar, M.Z.; Mohamed, I.F.; Othman, N.K.; Elabar, D.M.; Haider, F.I.; Samat, S.; Irfan, O.M. Effect of Semisolid and Heat Treatment Process on Microstructural Refinement of Al–7Si Alloy. Materials 2023, 16, 1086. https://doi.org/10.3390/ma16031086
Gebril MA, Omar MZ, Mohamed IF, Othman NK, Elabar DM, Haider FI, Samat S, Irfan OM. Effect of Semisolid and Heat Treatment Process on Microstructural Refinement of Al–7Si Alloy. Materials. 2023; 16(3):1086. https://doi.org/10.3390/ma16031086
Chicago/Turabian StyleGebril, Mohamed Abdelgawad, Mohd Zaidi Omar, Intan Fadhlina Mohamed, Norinsan Kamil Othman, Dawod Mohamed Elabar, Farag Ibrahim Haider, Saziana Samat, and Osama M. Irfan. 2023. "Effect of Semisolid and Heat Treatment Process on Microstructural Refinement of Al–7Si Alloy" Materials 16, no. 3: 1086. https://doi.org/10.3390/ma16031086