This study systematically investigates the anisotropic mechanical behavior and microstructural evolution of AlSi10Mg alloy processed through selective laser melting (SLM) additive manufacturing and 3D-printed sand casting (3DP). The research highlights critical differences in manufacturing-induced characteristics and their implications for industrial applications.
1. Material Characteristics and Processing Parameters
The chemical composition of gas-atomized AlSi10Mg powder for SLM processing is detailed in Table 1. The powder exhibits excellent flowability (Hall flow rate: 97 s/50 g) and optimal packing density (tap density: 1.61 g/cm³), crucial for layer-wise deposition.
| Element | Si | Mg | Fe | Cu | Mn | Ni | Ti | Al |
|---|---|---|---|---|---|---|---|---|
| wt.% | 10.20 | 0.31 | 0.06 | <0.01 | <0.01 | <0.01 | <0.01 | Bal. |
For sand casting, resin-coated silica sand (100-140 mesh) with compressive strength of 6.1 MPa and gas evolution of 13 mL/g at 850°C was utilized. The thermal treatment schedules are mathematically expressed as:
SLM Stress Relief:
$$T(t) = 300^{\circ}C \cdot \left(1 – e^{-t/7200}\right) \quad \text{for } t \leq 7200 \text{ s}$$
Sand Casting T6 Treatment:
$$T_{\text{solid solution}} = 535^{\circ}C \cdot \left(1 – e^{-t/14400}\right)$$
$$T_{\text{aging}} = 155^{\circ}C \cdot \left(1 – e^{-t/28800}\right)$$
2. Microstructural Analysis
SLM-processed specimens exhibited distinct anisotropic features:
- 0° build direction: Parallel melt pool boundaries with fine cellular α-Al(Si) structure (cell size: 0.5-1 μm)
- 45° orientation: Fish-scale melt pool morphology with Si-rich eutectic networks
- 90° vertical build: Columnar grain growth (aspect ratio >5:1) along thermal gradient
Sand casting produced coarse dendritic structures (secondary dendrite arm spacing: 25-40 μm) with needle-shaped eutectic Si particles (>10 μm length). The microstructure evolution follows:
$$\lambda_{SDAS} = 100 \cdot \dot{T}^{-1/3}$$
where λSDAS is secondary dendrite arm spacing (μm) and $\dot{T}$ is cooling rate (°C/s).
3. Mechanical Performance Comparison
| Process | Condition | YS (MPa) | UTS (MPa) | Elongation (%) | Hardness (HB) |
|---|---|---|---|---|---|
| SLM | As-built | 254-295 | 360-385 | 3.2-5.1 | 125±3 |
| 300°C/2h | 230-240 | 340-350 | 8.2-10.5 | 115±2 | |
| Sand Casting | As-cast | 140±15 | 195±20 | 3.2±0.5 | 75±5 |
| T6 | 210±20 | 240±25 | 1.5±0.3 | 95±4 |
The anisotropic strength variation in SLM specimens follows:
$$\Delta \sigma_{0^{\circ}-90^{\circ}} = 20 \cdot \cos \theta \quad \text{(MPa per 45^{\circ} orientation change)}$$
Eliminated through stress-relief annealing due to dislocation network rearrangement:
$$\rho_d = \rho_0 \cdot e^{-Q/RT}$$
where ρd = dislocation density, Q = activation energy (85 kJ/mol for AlSi10Mg), R = gas constant.
4. Fractographic Analysis
SLM fracture surfaces exhibited:
- Dimple size: 2-5 μm
- Unmelted particle fraction: <0.3%
- Gas porosity: 0.05-0.2%
Sand casting failures showed:
- Cleavage facets >50 μm
- Shrinkage porosity: 1.2-3.5%
- Oxide film density: 15-20/mm²
5. Process Optimization Strategies
For sand casting applications requiring high complexity:
$$t_{\text{cycle}} = 1.5 \cdot V^{0.33} \quad \text{(hours)}$$
where V is mold volume (dm³). SLM process windows satisfy:
$$P = 400 \cdot v^{0.5} \cdot h^{0.8}$$
P = laser power (W), v = scan speed (mm/s), h = layer thickness (μm).
6. Industrial Implementation Considerations
When comparing sand casting and additive manufacturing:
| Parameter | Sand Casting | SLM |
|---|---|---|
| Tooling cost | $5k-20k | $0 |
| Part cost (1-100 units) | $150-500/kg | $300-800/kg |
| Lead time | 4-8 weeks | 2-5 days |
| Max dimension | Unlimited | 400×400 mm |
The study demonstrates that while sand casting remains cost-effective for large-scale production, SLM provides superior mechanical performance and design freedom for complex, high-value components. Process selection should consider:
$$C_{\text{total}} = C_{\text{material}} + C_{\text{energy}} + C_{\text{post}} \cdot N^{-1}$$
where N = production quantity, Cpost = post-processing costs.