Through systematic material testing and process optimization, this study establishes critical parameters for producing engine cylinder blocks using vermicular graphite iron (VGI) with enhanced mechanical properties. The research focuses on achieving optimal vermicular rates while meeting RT450 strength requirements through controlled alloy additions and innovative casting techniques.
1. Material Composition Design
The chemical composition framework for VGI engine cylinder blocks follows:
| Element | Range (wt%) |
|---|---|
| C | 3.6-3.9 |
| Si | 2.1-2.4 |
| Mn | ≤0.5 |
| S | 0.03±0.005 |
| Cu | 0.6-0.8 |
| Sn | 0.03-0.05 |
The relationship between vermicular rate (VR) and key process parameters can be expressed as:
$$ VR = 89.7 – 125[Mg] – 98[RE] + 0.34T_p $$
Where [Mg] and [RE] represent magnesium and rare earth contents (wt%), and Tp is pouring temperature (°C).
2. Vermicularization Control
Optimal vermicular agent addition ranges were determined through systematic trials:
| S Content (wt%) | Vermicular Agent (%) | Vermicular Rate (%) |
|---|---|---|
| 0.028 | 0.8 | 65-75 |
| 0.030 | 0.7 | 80-85 |
| 0.032 | 0.6 | 85-95 |
The critical equation for mechanical properties optimization is:
$$ R_m = 250 + 180(VR/100) + 120[Cu] + 1500[Sn] $$
Where Rm represents tensile strength (MPa), and [Cu], [Sn] are alloy contents in wt%.
3. Rapid Casting Implementation
The 3D sand printing process parameters for engine cylinder block production include:
| Parameter | Value |
|---|---|
| Layer thickness | 0.3 mm |
| Binder saturation | 110% |
| Curing time | 12 s/layer |
| Post-processing | 200°C × 4h |
The casting process achieves dimensional accuracy better than CT9 with surface roughness Ra ≤ 12.5 μm, essential for complex engine cylinder block geometries.
4. Performance Validation
Mechanical properties from actual engine cylinder block sections:
| Location | Rm (MPa) | Rp0.2 (MPa) | Hardness (HB) |
|---|---|---|---|
| Bearing Cap | 487 | 388 | 229 |
| Cylinder Wall | 509 | 402 | 234 |
| Flange | 475 | 336 | 239 |
The microstructure evolution follows the relationship:
$$ P\% = 55[Cu] + 850[Sn] – 25(VR/100) $$
Where P% represents pearlite content, demonstrating effective matrix control through alloy additions.
5. Process Stability Analysis
Critical control parameters for consistent engine cylinder block production:
| Parameter | Control Range | Effect on VR |
|---|---|---|
| Mg Residual | 0.008-0.012% | ±15% VR |
| Pouring Temp | 1380-1420°C | ±5% VR |
| Mold Cooling | 3-5°C/s | ±8% VR |
Implementing these controls enables stable production of engine cylinder blocks with VR = 80-90% and Rm ≥ 450 MPa across all critical sections.