Investigation of the Effects of Solution Rapid Treatment on Wear Properties of AlSi10Mg Alloy

Technical Summary: Investigation of the Effects of Solution Rapid Treatment on Wear Properties of AlSi10Mg Alloy

Problem Statement
Additive manufacturing (AM) of AlSi10Mg alloys via Laser Powder Bed Fusion (L-PBF) produces components with high wear resistance in the as-built (AB) state due to their ultrafine cellular microstructure and continuous silicon (Si) network. However, these as-built parts often lack sufficient tensile strength and ductility for critical applications, necessitating post-processing heat treatments. The conventional T6 heat treatment (solutionizing at 540°C for 2 hours, water quenching, and artificial aging) improves mechanical properties but induces significant microstructural coarsening. Specifically, the dissolution of the fine Si network and the subsequent growth of Si particles lead to matrix softening and a reduction in wear resistance compared to the as-built state. Furthermore, traditional long-duration heat treatments are energy-intensive and reduce productivity, conflicting with sustainability goals. There is a need for an efficient post-processing route that enhances mechanical properties without compromising wear resistance or incurring excessive energy costs.

Methodology
The study utilized EOS M290 systems to produce AlSi10Mg parts using Direct Metal Laser Sintering (DMLS) with specific parameters (270 W laser power, 1300 mm/s scan speed, 36.43 J/mm³ energy density). The researchers compared four distinct conditions:

1. As-Built (AB): No heat treatment.
2. Conventional T6: Solutionizing at 540°C for 2 hours, water quenching (WQ), and aging at 160°C for 12 hours.
3. Rapid T6 (RT6): Four variations involving significantly shortened solutionization times (5 or 10 minutes) at temperatures of 510°C or 540°C, followed by WQ and the same aging cycle.

Characterization included optical microscopy, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and porosity analysis. Mechanical properties were assessed via hardness testing and tensile tests. Tribological performance was evaluated using a ball-on-flat reciprocating wear test (WC ball, 2 N load, 25 m sliding distance) under dry sliding conditions. Wear tracks were analyzed via 3D profiling and SEM/EDS to determine wear mechanisms.

Key Results

• Microstructural Evolution: The AB state exhibited a melt pool pattern with a continuous eutectic-Si network. Conventional T6 treatment caused the breakdown of this network, resulting in coarse, isolated Si particles (up to ~1.79 µm spacing) and a softened α-Al matrix. Rapid T6 treatments preserved a more homogeneous distribution of finer, spheroidized Si particles. The spacing between particles in the optimal rapid condition (RT6-3) was significantly smaller (1.17 µm) compared to conventional T6.
• Hardness and Mechanical Properties: The AB sample possessed the highest hardness (~120 HV) due to its fine cellular structure. Conventional T6 resulted in a significant hardness drop (softening). Rapid T6 treatments mitigated this softening; notably, the RT6-3 condition (540°C/5 min) retained higher hardness than the conventional T6 sample. While tensile strength values for rapid T6 were generally lower than AB, they were comparable to or slightly better than conventional T6, with significant improvements in ductility (elongation).
• Wear Performance:
  • Conventional T6: Exhibited the worst wear resistance among heat-treated samples, with a wear volume loss approximately 50% higher than the as-built state. This was attributed to Si coarsening and matrix softening.
  • Rapid T6: The RT6-3 condition (540°C for 5 minutes) achieved the lowest wear volume loss (0.165 mm³), representing a ~40% improvement in wear performance over conventional T6 and a ~30% improvement over the as-built state.
  • RT6-2 (510°C/10 min): Showed the highest wear volume loss among rapid treatments, nearly double that of RT6-3, indicating that specific time-temperature combinations are critical.
• Wear Mechanisms: Wear was primarily driven by oxidation and abrasion. The AB, RT6-1, and RT6-3 samples maintained stable, continuous oxide tribofilms, resulting in mild oxidative wear and smooth tracks. In contrast, the conventional T6 and RT6-2 samples experienced unstable oxide films, leading to severe adhesive wear, delamination, and deep grooving.

Key Contributions
The paper demonstrates that rapid solution treatment (RT6) is a viable alternative to conventional T6 for AM AlSi10Mg alloys. The primary contribution is the identification of an optimal rapid T6 route (540°C for 5 minutes) that:

1. Enhances Wear Resistance: Outperforms both the as-built and conventional T6 conditions by maintaining a refined microstructure that supports stable tribofilm formation.
2. Preserves Hardness: Avoids the extensive softening associated with long-duration solution treatments by limiting Si particle growth.
3. Improves Efficiency: Offers a time- and energy-efficient post-processing strategy, reducing solutionization time from 2 hours to 5 minutes.

Significance and Claims
The authors claim that this study provides a significant industrial advancement for wear-critical and load-bearing AM AlSi10Mg components. By optimizing the heat treatment parameters, it is possible to overcome the trade-off between mechanical strengthening (often requiring T6) and wear resistance (often superior in the as-built state). The research validates that rapid T6 routes can produce a composite-like microstructure with spheroidized Si particles that balances strength, ductility, and wear resistance. The findings suggest that rapid thermal processing can mitigate the adverse effects of gas pore expansion and microstructural coarsening, offering a sustainable, cost-effective solution for high-performance additive manufacturing applications.